841 lines
21 KiB
ReStructuredText
841 lines
21 KiB
ReStructuredText
.. _asm_coding_guidelines:
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Assembly Language Coding Guidelines
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###################################
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.. contents::
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:local:
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General
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*******
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ASM-GN-01: One address shall not be declared by two labels
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==========================================================
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Compliant example::
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asm_showcase_1:
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movl $0x1, %eax
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.. rst-class:: non-compliant-code
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Non-compliant example::
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asm_showcase_1:
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asm_showcase_2:
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movl $0x1, %eax
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ASM-GN-02: Names reserved for use by the assembler shall not be used for any other purpose
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==========================================================================================
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Names defined by developers shall not be the same as an assembler directive,
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instruction prefix, instruction mnemonic, or register name.
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Compliant example::
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asm_showcase_1:
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movl $0x1, %eax
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asm_showcase_2:
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movl $0x2, %eax
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asm_showcase_3:
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movl $0x3, %eax
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.. rst-class:: non-compliant-code
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Non-compliant example::
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text:
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movl $0x1, %eax
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mov:
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movl $0x2, %eax
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eax:
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movl $0x3, %eax
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ASM-GN-03: All declared labels shall be used
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============================================
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Otherwise, the label shall be removed.
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Compliant example::
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asm_showcase_1:
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movl $0x1, %eax
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jmp asm_showcase_2
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/* do something */
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asm_showcase_2:
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movl $0x2, %eax
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.. rst-class:: non-compliant-code
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Non-compliant example::
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asm_showcase_1:
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movl $0x1, %eax
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/*
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* 'asm_showcase_2' is not used anywhere, including
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* all C source/header files and Assembly files.
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*/
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asm_showcase_2:
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movl $0x2, %eax
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ASM-GN-04: Magic numbers shall be used with restrictions
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========================================================
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Only the following cases shall be allowed:
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a) The magic number is defined as a MACRO with a name clearly indicating its
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meaning.
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b) The meaning of the magic number is clearly documented in the comments before
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its usage.
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c) The meaning of the magic number is straightforward in the specific context.
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Compliant example::
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.section .data
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showcase_data:
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/* 0xff000000 means <something> */
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.long 0xff000000
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.. rst-class:: non-compliant-code
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Non-compliant example::
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.section .data
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showcase_data:
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.long 0xff000000
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ASM-GN-05: Parentheses shall be used to set the operator precedence explicitly
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==============================================================================
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Compliant example::
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.section .data
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showcase_data:
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/* 0x1234 means <something> */
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.long 0x1234 * (0x1234 >> 2)
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.. rst-class:: non-compliant-code
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Non-compliant example::
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.section .data
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showcase_data:
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/* 0x1234 means <something> */
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.long 0x1234 * 0x1234 >> 2
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ASM-GN-06: .end directive statement shall be the last statement in an Assembly file
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===================================================================================
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This rule only applies to the Assembly file which uses .end directive. .end
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directive shall be the last statement in this case. All the statements past .end
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directive will not be processed by the assembler.
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Compliant example::
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#include <types.h>
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#include <spinlock.h>
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.macro asm_showcase_mov
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movl $0x1, %eax
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.endm
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.end
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.. rst-class:: non-compliant-code
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Non-compliant example::
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#include <types.h>
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.end
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#include <spinlock.h>
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.macro asm_showcase_mov
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movl $0x1, %eax
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.endm
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ASM-GN-07: Infinite loop shall not exist
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========================================
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Compliant example::
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asm_showcase_1:
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movl $0x1, %eax
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jmp asm_showcase_2
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/* do something */
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asm_showcase_2:
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movl $0x2, %eax
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.. rst-class:: non-compliant-code
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Non-compliant example::
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asm_showcase_1:
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movl $0x1, %eax
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jmp asm_showcase_1
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ASM-GN-08: All code shall be reachable
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======================================
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Compliant example::
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asm_showcase:
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movl %ebx, %eax
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test $0x400, %eax
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jne asm_test
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movl $0x2, %eax
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movl $0x3, %eax
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asm_test:
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movl $0x6, %eax
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.. rst-class:: non-compliant-code
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Non-compliant example::
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asm_showcase:
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movl %ebx, %eax
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jmp asm_test
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/* the following two lines have no chance to be executed */
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movl $0x2, %eax
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movl $0x3, %eax
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asm_test:
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movl $0x6, %eax
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ASM-GN-09: Far jump shall be used with restrictions
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===================================================
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Jumping to an instruction located in a different segment shall only be used for
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the following two cases:
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a) Code bit changes, such as change from 32-bit mode to 64-bit mode.
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b) System resumes from S3. In this case, Global Descriptor Table (GDT) is set by
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Bootloader/BIOS and far jump has to be used to correct the Code Segment (CS).
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Compliant example::
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.code32
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execution_32:
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/*
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* do something in 32-bit mode,
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* then,
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* perform a far jump to start executing in 64-bit mode
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*/
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ljmp $0x0008, $execution_64_2
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.code64
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execution_64_1:
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/* do something in 64-bit mode */
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execution_64_2:
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/* do something in 64-bit mode */
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.. rst-class:: non-compliant-code
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Non-compliant example::
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.data
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asm_showcase_data:
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.word 0x0008
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.code32
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execution_32:
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/* do something in 32-bit mode */
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ljmp $0x0008, $asm_showcase_data
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ASM-GN-10: Assembler directives shall be used with restrictions
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===============================================================
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Usage of the assembler directive refers to GNU assembler 'as' user manual. Only
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the following assembler directives may be used:
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1) .align
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2) .end
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3) .extern
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4) repeat related directives, including .rept and .endr
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5) global related directives, including .global and .globl
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6) macro related directives, including .altmacro, .macro, and .endm
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7) code bit related directives, including .code16, .code32, and .code64
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8) section related directives, including .section, .data, and .text
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9) number emission related directives, including .byte, .word, .short, .long,
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and .quad
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10) .org, which shall be used with restrictions. It shall only be used to
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advance the location counter due to code bit changes, such as change from 32-bit
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mode to 64-bit mode.
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Functions
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*********
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ASM-FN-01: Function shall have return statement
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===============================================
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Compliant example::
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asm_func_showcase:
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movl $0x2, %eax
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ret
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asm_showcase:
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movl $0x1, %eax
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call asm_func_showcase
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.. rst-class:: non-compliant-code
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Non-compliant example::
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asm_func_showcase:
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movl $0x2, %eax
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asm_showcase:
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movl $0x1, %eax
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call asm_func_showcase
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ASM-FN-02: A function shall only have one entry point
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=====================================================
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The label in a function shall only be used inside. Jumping into the function
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from outside via this label shall not be allowed. This rule applies to both
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conditional jump and unconditional jump.
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Compliant example::
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asm_func_showcase:
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test $0x400, %eax
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jne tmp
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movl $0x1, %eax
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tmp:
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movl $0x2, %eax
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ret
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asm_showcase:
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movl $0x1, %eax
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call asm_func_showcase
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.. rst-class:: non-compliant-code
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Non-compliant example::
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asm_func_showcase:
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movl $0x1, %eax
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tmp:
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movl $0x2, %eax
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ret
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asm_showcase:
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movl $0x1, %eax
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call asm_func_showcase
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jmp tmp
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ASM-FN-03: A function shall only have one return statement
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==========================================================
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Compliant example::
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asm_func_showcase:
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test $0x400, %eax
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jne tmp
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movl $0x2, %eax
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jmp showcase_return
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tmp:
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movl $0x3, %eax
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showcase_return:
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ret
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.. rst-class:: non-compliant-code
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Non-compliant example::
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asm_func_showcase:
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test $0x400, %eax
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jne tmp
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movl $0x2, %eax
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ret
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tmp:
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movl $0x3, %eax
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ret
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ASM-FN-04: Function shall only be entered by explicit call
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==========================================================
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Falling through from prior instruction shall not be allowed.
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Compliant example::
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asm_func_showcase:
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movl $0x2, %eax
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ret
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asm_showcase:
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movl $0x1, %eax
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call asm_func_showcase
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.. rst-class:: non-compliant-code
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Non-compliant example::
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asm_showcase:
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movl $0x1, %eax
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asm_func_showcase:
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movl $0x2, %eax
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ret
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ASM-FN-05: A jump instruction shall not be used to jump out of a function
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=========================================================================
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This rule applies to both conditional jump and unconditional jump.
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Compliant example::
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asm_func_showcase:
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movl $0x2, %eax
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ret
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asm_showcase:
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movl $0x1, %eax
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call asm_func_showcase
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.. rst-class:: non-compliant-code
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Non-compliant example::
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asm_func_showcase:
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movl $0x2, %eax
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jmp asm_test
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ret
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asm_showcase:
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movl $0x1, %ebx
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call asm_func_showcase
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asm_test:
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cli
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ASM-FN-06: Recursion shall not be used in function calls
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========================================================
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Compliant example::
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asm_func_showcase:
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movl $0x2, %eax
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ret
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asm_showcase:
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movl $0x1, %eax
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call asm_func_showcase
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.. rst-class:: non-compliant-code
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Non-compliant example::
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asm_func_showcase:
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movl $0x2, %eax
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call asm_func_showcase
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ret
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asm_showcase:
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movl $0x1, %eax
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call asm_func_showcase
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ASM-FN-07: Cyclomatic complexity shall be less than 10
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======================================================
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A function with cyclomatic complexity greater than 10 shall be split into
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multiple sub-functions to simplify the function logic.
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Compliant example::
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asm_func_showcase:
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/* do something */
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cmpl $0x0, %eax
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je tmp
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cmpl $0x1, %eax
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je tmp
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cmpl $0x2, %eax
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je tmp
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/* do something */
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tmp:
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/* do something */
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ret
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.. rst-class:: non-compliant-code
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Non-compliant example::
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asm_func_showcase:
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/* do something */
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cmpl $0x0, %eax
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je tmp
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cmpl $0x1, %eax
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je tmp
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cmpl $0x2, %eax
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je tmp
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cmpl $0x3, %eax
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je tmp
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cmpl $0x4, %eax
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je tmp
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cmpl $0x5, %eax
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je tmp
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cmpl $0x6, %eax
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je tmp
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cmpl $0x7, %eax
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je tmp
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cmpl $0x8, %eax
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je tmp
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cmpl $0x9, %eax
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je tmp
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cmpl $0xa, %eax
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je tmp
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cmpl $0xb, %eax
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je tmp
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cmpl $0xc, %eax
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je tmp
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cmpl $0xd, %eax
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je tmp
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cmpl $0xe, %eax
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je tmp
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/* do something */
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tmp:
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/* do something */
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ret
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Coding Style
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************
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ASM-CS-01: One instruction statement shall not be split into multiple lines
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===========================================================================
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Compliant example::
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movl $0x2, %eax
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.. rst-class:: non-compliant-code
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Non-compliant example::
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movl $0x2, \
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%eax
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ASM-CS-02: Assembler directive statements shall be aligned
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==========================================================
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An assembler directive statement is composed of directive and arguments.
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Arguments are optional depending on the use case.
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Some detailed rules about the alignment are listed below:
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a) Assembler directives shall be aligned with one tab if the statement is in the
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code block under any label from functional perspective. Otherwise, assembler
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directives shall be aligned to the start of the line.
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b) Tabs shall be used to separate the directive and the first argument, where
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applicable. The number of tabs could be decided by the developers based on each
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case and it shall guarantee that the first argument is aligned in each directive
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block.
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c) A single space shall be used to separate multiple arguments.
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Compliant example::
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.extern cpu_primary_save32
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.extern cpu_primary_save64
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.section multiboot_header, "a"
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.align 4
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.long 0x0008
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.long 0x0018
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.section entry, "ax"
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.align 8
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.code32
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.. rst-class:: non-compliant-code
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Non-compliant example::
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.extern cpu_primary_save32
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.extern cpu_primary_save64
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.section multiboot_header, "a"
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.align 4
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.long 0x0008
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.long 0x0018
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.section entry, "ax"
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.align 8
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.code32
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ASM-CS-03: Labels shall be aligned to the start of the line
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===========================================================
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Compliant example::
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asm_showcase_1:
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movl $0x1, %eax
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asm_showcase_2:
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movl $0x2, %eax
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.. rst-class:: non-compliant-code
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Non-compliant example::
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asm_showcase_1:
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movl $0x1, %eax
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asm_showcase_2:
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movl $0x2, %eax
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ASM-CS-04: Instruction statements shall be aligned
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==================================================
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An instruction statement is composed of instruction prefix, instruction
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mnemonic, and instruction operands. Instruction prefix and instruction operands
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are optional depending on the use case.
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Some detailed rules about the alignment are listed below:
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a) The start of instruction statements shall be aligned with one tab if the
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instruction statement is in the code block under any label from functional
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perspective. Otherwise, the start of instruction statements shall be aligned to
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the start of the line. The start of the instruction could either be the
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instruction mnemonic or the instruction prefix.
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b) One space shall be used to separate the instruction prefix and the
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instruction mnemonic, where applicable.
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c) Tabs shall be used to separate the instruction mnemonic and the first
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instruction operand, where applicable. The number of tabs could be decided by
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the developers based on each case and it shall guarantee that the first
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instruction operand in the code block under one label is aligned.
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d) A single space shall be used to separate multiple operands.
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Compliant example::
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asm_showcase_1:
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movl $0x1, %eax
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lock and %rcx, (%rdx)
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asm_showcase_2:
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movl $0x3, %eax
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.. rst-class:: non-compliant-code
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Non-compliant example::
|
|
|
|
asm_showcase_1:
|
|
movl $0x1, %eax
|
|
lock and %rcx, (%rdx)
|
|
|
|
asm_showcase_2:
|
|
movl $0x2, %eax
|
|
|
|
|
|
ASM-CS-05: '//' shall not be used for comments
|
|
===============================================
|
|
|
|
'/* \*/' shall be used to replace '//' for comments.
|
|
|
|
Compliant example::
|
|
|
|
/* This is a comment */
|
|
movl $0x1, %eax
|
|
|
|
.. rst-class:: non-compliant-code
|
|
|
|
Non-compliant example::
|
|
|
|
// This is a comment
|
|
movl $0x1, %eax
|
|
|
|
|
|
ASM-CS-06: Tabs shall be 8 characters wide
|
|
==========================================
|
|
|
|
A tab character shall be considered 8-character wide when limiting the line
|
|
width.
|
|
|
|
|
|
ASM-CS-07: Each line shall contain at most 120 characters
|
|
=========================================================
|
|
|
|
No more than 120 characters shall be on a line, with tab stops every 8
|
|
characters.
|
|
|
|
Compliant example::
|
|
|
|
/*
|
|
* This is a comment. This is a comment. This is a comment. This is a comment.
|
|
* This is a comment. This is a comment. This is a comment.
|
|
*/
|
|
|
|
.. rst-class:: non-compliant-code
|
|
|
|
Non-compliant example::
|
|
|
|
/* This is a comment. This is a comment. This is a comment. This is a comment. This is a comment. This is a comment. This is a comment. */
|
|
|
|
|
|
ASM-CS-08: Legal entity shall be documented in every file
|
|
=========================================================
|
|
|
|
Legal entity shall be documented in a separate comments block at the start of
|
|
every file.
|
|
The following information shall be included:
|
|
|
|
a) Copyright
|
|
b) License (using an `SPDX-License-Identifier <https://spdx.org/licenses/>`_)
|
|
|
|
Compliant example::
|
|
|
|
/* Legal entity shall be placed at the start of the file. */
|
|
-------------File Contents Start After This Line------------
|
|
|
|
/*
|
|
* Copyright (C) 2019 Intel Corporation.
|
|
*
|
|
* SPDX-License-Identifier: BSD-3-Clause
|
|
*/
|
|
|
|
/* Coding or implementation related comments start after the legal entity. */
|
|
.code64
|
|
|
|
.. rst-class:: non-compliant-code
|
|
|
|
Non-compliant example::
|
|
|
|
/* Neither copyright nor license information is included in the file. */
|
|
-------------------File Contents Start After This Line------------------
|
|
|
|
/* Coding or implementation related comments start directly. */
|
|
.code64
|
|
|
|
|
|
|
|
Naming Convention
|
|
*****************
|
|
|
|
ASM-NC-01: Lower case letters shall be used for case insensitive names
|
|
======================================================================
|
|
|
|
This rule applies to assembler directive, instruction prefix, instruction
|
|
mnemonic, and register name.
|
|
|
|
Compliant example::
|
|
|
|
.code64
|
|
lock and %rcx, (%rdx)
|
|
|
|
.. rst-class:: non-compliant-code
|
|
|
|
Non-compliant example::
|
|
|
|
.CODE64
|
|
LOCK AND %RCX, (%RDX)
|
|
|
|
|
|
ASM-NC-02: Names defined by developers shall use lower case letters
|
|
===================================================================
|
|
|
|
Names defined by developers shall use lower case letters with the following
|
|
exception. If an object-like MACRO is defined with '#define', it shall be named
|
|
with full upper case.
|
|
|
|
Compliant example::
|
|
|
|
asm_showcase:
|
|
movl $0x1, %eax
|
|
|
|
.. rst-class:: non-compliant-code
|
|
|
|
Non-compliant example::
|
|
|
|
ASM_SHOWCASE:
|
|
movl $0x1, %eax
|
|
|
|
|
|
ASM-NC-03: Label name shall be unique
|
|
=====================================
|
|
|
|
Label name shall be unique with the following exception. Usage of local labels
|
|
is allowed. Local label is defined with the format 'N:', where N represents any
|
|
non-negative integer. Using 'Nb' to refer to the most recent previous definition
|
|
of that label. Using 'Nf' to refer to the next definition of a local label.
|
|
|
|
Compliant example::
|
|
|
|
asm_showcase_1:
|
|
movl $0x1, %eax
|
|
|
|
asm_showcase_2:
|
|
movl $0x2, %eax
|
|
|
|
.. rst-class:: non-compliant-code
|
|
|
|
Non-compliant example::
|
|
|
|
asm_showcase:
|
|
movl $0x1, %eax
|
|
|
|
asm_showcase:
|
|
movl $0x2, %eax
|
|
|
|
|
|
ASM-NC-04: Names defined by developers shall be less than 31 characters
|
|
=======================================================================
|
|
|
|
Compliant example::
|
|
|
|
asm_showcase:
|
|
movl $0x1, %eax
|
|
|
|
.. rst-class:: non-compliant-code
|
|
|
|
Non-compliant example::
|
|
|
|
asm_showcase_asm_showcase_asm_showcase:
|
|
movl $0x1, %eax
|
|
|
|
|
|
|
|
ABI Conformance
|
|
***************
|
|
|
|
ASM-ABI-01: The implementation of Assembly code shall conform to the System V x86/AMD ABI
|
|
=========================================================================================
|
|
|
|
The implementation of Assembly code shall conform to the function calling
|
|
sequence defined in System V Application Binary Interface AMD64 Architecture
|
|
Processor Supplement.
|
|
|
|
|
|
Refer to the `System V Application Binary Interface AMD64 Architecture Processor Supplement <https://software.intel.com/sites/default/files/article/402129/mpx-linux64-abi.pdf>`_.
|