[PATCH] riscv: Use memcpy to handle unaligned access when fixing R_RISCV_RELATIVE

[Adhemerval Zanella]

> 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
>