[PATCH v1 1/3] aarch64: Fix IMAGE_REL_ARM64_PAGEBASE_REL21 relocation and symbol reduction for relocations

[Evgeny Karpov]

Friday, September 6, 2024
Martin Storsjö <martin@martin.st> wrote:

> entry:
>          adrp x0, symbol_in_same_page
>          add x0, x0, :lo12:symbol_in_same_page
>          adrp x0, symbol_in_same_page+108
>          add x0, x0, :lo12:symbol_in_same_page+108
         
> The output instruction sequence is the exact same in the case of all 3 
> linkers - the only thing that differs is the amount of symbols retained.

> Now if you apply your patch and redo the last example, linked with GNU ld, 
> the output adrp relocations turn out wrong. Previously all 3 linkers 
> agree. Thus I think your patch is wrong, and the current handling of this 
> relocation in binutils is correct.

In the case of this patch, the offset should be excluded from
relocation instructions.

adrp x0, symbol_in_same_page
add x0, x0, :lo12:symbol_in_same_page
add x0, x0, 108

It produces the same result for all three linkers. This is the 
reason why offset usage was avoided in the GCC patch series
for aarch64-w64-mingw32.
https://gcc.gnu.org/pipermail/gcc-patches/2024-September/662499.html

0000000140001010: B0000000  adrp        x0,0000000140002000
0000000140001014: 913F1000  add         x0,x0,#0xFC4
0000000140001018: 9101B000  add         x0,x0,#0x6C
...
0000000140003030: D503201F  nop

Regards,
Evgeny