Until now, linker-tool-gcc.h was used when LLD linker was chosen.
This causes linking issues because for GNU LD we use ALIGN_WITH_INPUT
attribute which is not available in LLVM LLD.
When using GNU LD we have to use ALIGN_WITH_INPUT to make sure that the
difference between VMA and LMA remains the same between output sections
that have different memory regions for VMA and LMA (RAM and FLASH).
With ALIGN_WITH_INPUT it's safe to do the memcpy of sections
that needs to be copied from flash to RAM in one function call:
(from z_data_copy() in kernel/xip.c)
```
z_early_memcpy(&__data_region_start, &__data_region_load_start,
__data_region_end - __data_region_start);
```
By default, LLVM LLD aligns both VMA and LMA to the same value, but
when --omagic (-N) option is provided then only the first output section
of given region has aligned LMA and the difference between VMA addresses
(0 is this is the first section) is added.
As a result the difference between LMA and VMA is constant for every
section, so this emulates ALIGN_WITH_INPUT option present in GNU LD
(required by XIP systems).
The --omagic flag is defined in cmake/linker/lld/target_baremetal.cmake
Example:
```
MEMORY {
ROM : ORIGIN = 0x1000, LENGTH = 1K
RAM : ORIGIN = 0x11000, LENGTH = 1K
}
SECTIONS {
.text 0x1000 : {
*(.text*)
} >ROM
.data.rel.ro : {
*(.data.rel.ro)
} >RAM AT>ROM
.data : {
*(.data*)
} >RAM AT>ROM
}
```
```
echo '.globl _start; _start: nop; .byte 1;'\
'.data.rel.ro; .balign 16; .byte 0;'\
'.data; .balign 32; .byte 0;' | \
llvm-mc -filetype=obj -triple=arm - -o test.o
armv7m-cros-eabi-ld.lld --sort-section=alignment -N -T script.ld \
test.o -o lld_out
```
```
Idx Name Size VMA LMA File off Algn
0 .text 00000005 00001000 00001000 00000094 2**2
1 .data.rel.ro 00000001 00011000 00001010 000000a0 2**4
2 .data 00000001 00011020 00001030 000000c0 2**5
```
In this example the first section has lower alignment than the following
section, but with -N option the difference between VMA and LMA is the
same for .data.rel.ro and .data sections.
For comparison, using BFD linker with --omagic option results in the
following:
```
Idx Name Size VMA LMA File off Algn
0 .text 00000005 00001000 00001000 00000094 2**2
1 .data.rel.ro 00000001 00011000 00001005 000000a0 2**4
2 .data 00000001 00011020 00001006 000000c0 2**5
```
with ALIGN_WITH_INPUT added, GNU LD adds the difference between VMA to
LMA, but doesn't align LMA of .data.rel.ro section:
```
Idx Name Size VMA LMA File off Algn
0 .text 00000005 00001000 00001000 00000074 2**2
1 .data.rel.ro 00000001 00011000 00001005 00000080 2**4
2 .data 00000001 00011020 00001025 000000a0 2**5
```
Signed-off-by: Patryk Duda <pdk@semihalf.com>
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