Commit 61c6065e authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

objtool: Allow !PC relative relocations 



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: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220915111145.806607235@infradead.org
parent 5b71ac8a

tools/objtool/arch/x86/decode.c

+24 −0
Original line number Diff line number Diff line
@@ -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; \

tools/objtool/check.c

+1 −1
Original line number Diff line number Diff line
@@ -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",

tools/objtool/include/objtool/arch.h

+2 −0
Original line number Diff line number Diff line
@@ -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 */