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arm: Avoid UB in elf_machine_rel()

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This recently came up during a cleanup to remove misaligned accesses
from the RISC-V port.

Link: https://sourceware.org/pipermail/libc-alpha/2022-June/139961.html
Suggested-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Reviewed-by: Fangrui Song <maskray@google.com>
This commit is contained in:
Palmer Dabbelt 2022-06-23 14:49:32 -07:00 • committed by Andreas K. Hüttel
parent a10b6ad471
commit 07fe71f59b
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GPG key ID: DC2B16215ED5412A
1 changed files with 4 additions and 5 deletions
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9
sysdeps/arm/dl-machine.h
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@ -349,10 +349,7 @@ elf_machine_rel (struct link_map *map, struct r_scope_elem *scope[],
break; break;
case R_ARM_ABS32: case R_ARM_ABS32:
{ {
struct unaligned ElfW(Addr) tmp;
{
Elf32_Addr x;
} __attribute__ ((packed, may_alias));
# ifndef RTLD_BOOTSTRAP # ifndef RTLD_BOOTSTRAP
/* This is defined in rtld.c, but nowhere in the static /* This is defined in rtld.c, but nowhere in the static
libc.a; make the reference weak so static programs can libc.a; make the reference weak so static programs can
@ -372,7 +369,9 @@ elf_machine_rel (struct link_map *map, struct r_scope_elem *scope[],
value -= SYMBOL_ADDRESS (map, refsym, true); value -= SYMBOL_ADDRESS (map, refsym, true);
# endif # endif
/* Support relocations on mis-aligned offsets. */ /* Support relocations on mis-aligned offsets. */
((struct unaligned *) reloc_addr)->x += value; memcpy (&tmp, reloc_addr, sizeof tmp);
tmp += value;
memcpy (reloc_addr, &tmp, sizeof tmp);
break; break;
} }
case R_ARM_TLS_DESC: case R_ARM_TLS_DESC: