riscv: Use memcpy to handle unaligned access when fixing R_RISCV_RELATIVE
Checks
Context |
Check |
Description |
dj/TryBot-apply_patch |
success
|
Patch applied to master at the time it was sent
|
dj/TryBot-32bit |
success
|
Build for i686
|
Commit Message
Although RISC-V Linux will enable the unaligned memory access handler by
default, that is quite expensive in general, using memcpy will be much cheaper
- just break down that into several load/store byte instructions.
ARM and MIPS has similar issue:
ARM: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51456
MIPS: https://gcc.gnu.org/legacy-ml/gcc-help/2005-07/msg00325.html
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
---
sysdeps/riscv/dl-machine.h | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
Comments
> On 24 Jun 2022, at 05:25, Kito Cheng <kito.cheng@sifive.com> wrote:
>
> Although RISC-V Linux will enable the unaligned memory access handler by
> default, that is quite expensive in general, using memcpy will be much cheaper
> - just break down that into several load/store byte instructions.
>
> ARM and MIPS has similar issue:
>
> ARM: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51456
> MIPS: https://gcc.gnu.org/legacy-ml/gcc-help/2005-07/msg00325.html
>
> Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
LGTM, thanks.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
> ---
> sysdeps/riscv/dl-machine.h | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/sysdeps/riscv/dl-machine.h b/sysdeps/riscv/dl-machine.h
> index 4bb858adaa..a880567c3c 100644
> --- a/sysdeps/riscv/dl-machine.h
> +++ b/sysdeps/riscv/dl-machine.h
> @@ -157,7 +157,10 @@ __attribute__ ((always_inline))
> elf_machine_rela_relative (ElfW(Addr) l_addr, const ElfW(Rela) *reloc,
> void *const reloc_addr)
> {
> - *(ElfW(Addr) *) reloc_addr = l_addr + reloc->r_addend;
> + /* R_RISCV_RELATIVE might located in debug info section which might not
> + aligned to XLEN bytes. Also support relocations on unaligned offsets. */
> + ElfW(Addr) value = l_addr + relic->r_addend;
> + memcpy (reloc_addr, &value, sizeof value);
> }
>
> /* Perform a relocation described by R_INFO at the location pointed to
> --
> 2.34.0
>
@@ -157,7 +157,10 @@ __attribute__ ((always_inline))
elf_machine_rela_relative (ElfW(Addr) l_addr, const ElfW(Rela) *reloc,
void *const reloc_addr)
{
- *(ElfW(Addr) *) reloc_addr = l_addr + reloc->r_addend;
+ /* R_RISCV_RELATIVE might located in debug info section which might not
+ aligned to XLEN bytes. Also support relocations on unaligned offsets. */
+ ElfW(Addr) value = l_addr + relic->r_addend;
+ memcpy (reloc_addr, &value, sizeof value);
}
/* Perform a relocation described by R_INFO at the location pointed to