247 lines
6.8 KiB
ArmAsm
247 lines
6.8 KiB
ArmAsm
/*
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* Copyright (c) 2016 Cadence Design Systems, Inc.
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* SPDX-License-Identifier: Apache-2.0
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*/
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/*
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* For the Xtensa simulator target, this code sets up the C calling context
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* and calls main() (via __clibrary_start).
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* Control arrives here at _start from the reset vector or from crt0-app.S.
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*/
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#include <xtensa/simboard.h>
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#include <xtensa/simcall.h>
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#include <xtensa/coreasm.h>
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/* Exports */
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.global _start
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.global __start
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/*
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* Imports
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* __clibrary_init from C library (eg. newlib or uclibc)
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* exit from C library
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* main from user application
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* __stack from linker script (see LSP Ref Manual)
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*/
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.type __clibrary_init, @function
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.type _Cstart, @function
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.type exit, @function
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/* Macros to abstract away ABI differences */
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#if __XTENSA_CALL0_ABI__
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# define CALL call0
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# define CALLX callx0
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# define ARG1 a2 /* 1st outgoing call argument */
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# define ARG2 a3 /* 2nd outgoing call argument */
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# define ARG3 a4 /* 3rd outgoing call argument */
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# define ARG4 a5 /* 4th outgoing call argument */
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# define ARG5 a6 /* 5th outgoing call argument */
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#else
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# define CALL call4
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# define CALLX callx4
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# define ARG1 a6 /* 1st outgoing call argument */
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# define ARG2 a7 /* 2nd outgoing call argument */
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# define ARG3 a8 /* 3rd outgoing call argument */
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# define ARG4 a9 /* 4th outgoing call argument */
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# define ARG5 a10 /* 5th outgoing call argument */
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#endif
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.data
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.weak _start_envp /* allow overriding */
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.align 4
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_start_envp: .word 0 /* empty environ */
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.text
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.align 4
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_start:
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__start:
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/*
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* _start is typically NOT at the beginning of the text segment --
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* it is always called from either the reset vector or other code
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* that does equivalent initialization (such as crt0-app.S).
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*
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* Assumptions on entry to _start:
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* - low (level-one) and medium priority interrupts are disabled
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* via PS.INTLEVEL and/or INTENABLE (PS.INTLEVEL is expected to
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* be zeroed, to potentially enable them, before calling main)
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* - C calling context not initialized:
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* - PS not initialized
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* - SP not initialized
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* - the following are initialized:
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* - LITBASE, cache attributes, WindowBase, WindowStart,
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* CPENABLE, FP's FCR and FSR, EXCSAVE[n]
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* Keep a0 zero. It is used to initialize a few things.
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* It is also the return address, where zero indicates
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* that the frame used by _start is the bottommost frame.
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*
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*/
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movi a0, 0 /* keep this register zero. */
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#if XTOS_RESET_UNNEEDED
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#include "reset-unneeded.S"
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#endif
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/*
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* Initialize the stack pointer.
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* See the "ABI and Software Conventions" chapter in the
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* Xtensa ISA Reference manual for details.
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*
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* NOTE: Because the _start routine does not use any memory in its
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* stack frame, and because all of its CALL instructions use a
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* window size of 4, the stack frame for _start can be empty.
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*/
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movi sp, __stack
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/*
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* reserve stack space for
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* - argv array
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* - argument strings
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*/
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movi a2, SYS_iss_argv_size
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simcall /* returns size of argv[] + its strings in a2 */
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#if XCHAL_HAVE_PIF
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/*
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* The stack only needs 16-byte alignment. However, here we round up
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* the argv size further to 128 byte multiples so that in most cases,
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* variations in argv[0]'s path do not result in different stack
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* allocation. Otherwise, such variations can impact execution timing
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* (eg. due to cache effects etc) for the same code and data. If we
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* have a PIF, it's more likely the extra required space is okay.
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*/
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addi a2, a2, 127
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srli a2, a2, 7
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slli a2, a2, 7
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#else
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/* Keep stack 16-byte aligned. */
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addi a2, a2, 15
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srli a2, a2, 4
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slli a2, a2, 4
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#endif
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/*
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* No need to use MOVSP because we have no caller (we're the
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* base caller); in fact it's better not to use MOVSP in this
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* context, to avoid unnecessary ALLOCA exceptions and copying
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* from undefined memory:
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* sub a3, sp, a2
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* movsp sp, a3
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*/
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sub sp, sp, a2
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/*
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* Now that sp (a1) is set, we can set PS as per the application (user
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* vector mode, enable interrupts, enable window exceptions if
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* applicable).
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*/
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#if XCHAL_HAVE_EXCEPTIONS
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# ifdef __XTENSA_CALL0_ABI__
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/* PS.WOE = 0, PS.UM = 1, PS.EXCM = 0, PS.INTLEVEL = 0 */
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movi a3, PS_UM
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# else
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/* PS.WOE = 1, PS.UM = 1, PS.EXCM = 0, PS.INTLEVEL = 0 */
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movi a3, PS_UM|PS_WOE
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# endif
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wsr a3, PS
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rsync
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#endif
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/*
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* Do any initialization that affects the memory map, such as
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* setting up TLB entries, that needs to be done before we can
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* successfully clear BSS (e.g. if some BSS segments are in
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* remapped areas).
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*
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* NOTE: This hook works where the reset vector does not unpack
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* segments (see "ROM packing" in the LSP manual), or where
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* unpacking of segments is not affected by memory remapping.
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* If ROM unpacking is affected, TLB setup must be done in
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* assembler from the reset vector.
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*
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* The __memmap_init() routine can be a C function, however it
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* does not have BSS initialized! In particular, __memmap_init()
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* cannot set BSS variables, i.e. uninitialized global variables
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* (they'll be wiped out by the following BSS clear), nor can it
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* assume they are yet initialized to zero.
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*
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* The __memmap_init() function is optional. It is marked as a
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* weak symbol, so that it gets valued zero if not defined.
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*/
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.weak __memmap_init
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movi a4, __memmap_init
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beqz a4, 1f
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CALLX a4
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1:
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/* The new ISS simcall only appeared after RB-2007.2: */
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#if !XCHAL_HAVE_BOOTLOADER && \
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(XCHAL_HW_MAX_VERSION > XTENSA_HWVERSION_RB_2007_2)
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/* pre-LX2 cores only */
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/*
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* Clear the BSS (uninitialized data) segments.
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* This code supports multiple zeroed sections (*.bss).
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* For speed, we clear memory using an ISS simcall
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* (see crt1-boards.S for more generic BSS clearing code).
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*/
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movi a6, _bss_table_start
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movi a7, _bss_table_end
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bgeu a6, a7, .Lnobss
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.Lbssloop:
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movi a2, SYS_memset
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l32i a3, a6, 0 /* arg1 = fill start address */
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movi a4, 0 /* arg2 = fill pattern */
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l32i a5, a6, 4 /* get end address */
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addi a6, a6, 8 /* next bss table entry */
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sub a5, a5, a3 /* arg3 = fill size in bytes */
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simcall /* memset(a3,a4,a5) */
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bltu a6, a7, .Lbssloop /* loop until end of bss table */
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.Lnobss:
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#endif
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/*
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* Call __clibrary_init to initialize the C library:
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*
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* void __clibrary_init(int argc, char ** argv, char ** environ,
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* void(*init_func)(void), void(*fini_func)(void));
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*/
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/* Get argv with the arguments from the ISS */
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mov a3, sp /* tell simcall where to write argv[] */
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movi a2, SYS_iss_set_argv
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simcall /* write argv[] array at a3 */
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movi a2, SYS_iss_argc
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simcall /* put argc in a2 */
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/* Call: int _Cstart(); */
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CALL _Cstart
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/* The return value is the same register as the first outgoing
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* argument.
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*/
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CALL exit
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/* Does not return here. */
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.size _start, . - _start
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/*
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* Local Variables:
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* mode:fundamental
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* comment-start: "/* "
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* comment-start-skip: "/* *"
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* End:
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*/
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