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objtool: Allow !PC relative relocations

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Objtool doesn't currently much like per-cpu usage in alternatives:

arch/x86/entry/entry_64.o: warning: objtool: .altinstr_replacement+0xf: unsupported relocation in alternatives section
  f:   65 c7 04 25 00 00 00 00 00 00 00 80     movl   $0x80000000,%gs:0x0      13: R_X86_64_32S        __x86_call_depth

Since the R_X86_64_32S relocation is location invariant (it's
computation doesn't include P - the address of the location itself),
it can be trivially allowed.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220915111145.806607235@infradead.org
This commit is contained in:
Peter Zijlstra 2022-09-15 13:11:07 +02:00
parent 5b71ac8a2a
commit 61c6065ef7
3 changed files with 27 additions and 1 deletions
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24
tools/objtool/arch/x86/decode.c
View file

@ -73,6 +73,30 @@ unsigned long arch_jump_destination(struct instruction *insn)
return insn->offset + insn->len + insn->immediate;
}
bool arch_pc_relative_reloc(struct reloc *reloc)
{
/*
* All relocation types where P (the address of the target)
* is included in the computation.
*/
switch (reloc->type) {
case R_X86_64_PC8:
case R_X86_64_PC16:
case R_X86_64_PC32:
case R_X86_64_PC64:
case R_X86_64_PLT32:
case R_X86_64_GOTPC32:
case R_X86_64_GOTPCREL:
return true;
default:
break;
}
return false;
}
#define ADD_OP(op) \
if (!(op = calloc(1, sizeof(*op)))) \
return -1; \

2
tools/objtool/check.c
View file

@ -1645,7 +1645,7 @@ static int handle_group_alt(struct objtool_file *file,
* accordingly.
*/
alt_reloc = insn_reloc(file, insn);
if (alt_reloc &&
if (alt_reloc && arch_pc_relative_reloc(alt_reloc) &&
!arch_support_alt_relocation(special_alt, insn, alt_reloc)) {
WARN_FUNC("unsupported relocation in alternatives section",

2
tools/objtool/include/objtool/arch.h
View file

@ -93,4 +93,6 @@ bool arch_is_rethunk(struct symbol *sym);
int arch_rewrite_retpolines(struct objtool_file *file);
bool arch_pc_relative_reloc(struct reloc *reloc);
#endif /* _ARCH_H */