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riscv: Use memcpy to handle unaligned access when fixing R_RISCV_RELATIVE

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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

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
This commit is contained in:
Kito Cheng 2022-06-28 21:52:19 +08:00 committed by Palmer Dabbelt
parent e9dd368296
commit c22d2021a9
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1 changed files with 4 additions and 1 deletions
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5
sysdeps/riscv/dl-machine.h
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@ -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 + reloc->r_addend;
memcpy (reloc_addr, &value, sizeof value);
}
/* Perform a relocation described by R_INFO at the location pointed to