Commit 6f5ec299 authored May 14, 2018 by Josh Poimboeuf Committed by Ingo Molnar May 15, 2018

objtool: Detect RIP-relative switch table references



Typically a switch table can be found by detecting a .rodata access
followed an indirect jump:

    1969:	4a 8b 0c e5 00 00 00 	mov    0x0(,%r12,8),%rcx
    1970:	00
			196d: R_X86_64_32S	.rodata+0x438
    1971:	e9 00 00 00 00       	jmpq   1976 <dispc_runtime_suspend+0xb6a>
			1972: R_X86_64_PC32	__x86_indirect_thunk_rcx-0x4

Randy Dunlap reported a case (seen with GCC 4.8) where the .rodata
access uses RIP-relative addressing:

    19bd:	48 8b 3d 00 00 00 00 	mov    0x0(%rip),%rdi        # 19c4 <dispc_runtime_suspend+0xbb8>
			19c0: R_X86_64_PC32	.rodata+0x45c
    19c4:	e9 00 00 00 00       	jmpq   19c9 <dispc_runtime_suspend+0xbbd>
			19c5: R_X86_64_PC32	__x86_indirect_thunk_rdi-0x4

In this case the relocation addend needs to be adjusted accordingly in
order to find the location of the switch table.

The fix is for case 3 (as described in the comments), but also make the
existing case 1 & 2 checks more precise by only adjusting the addend for
R_X86_64_PC32 relocations.

This fixes the following warnings:

  drivers/video/fbdev/omap2/omapfb/dss/dispc.o: warning: objtool: dispc_runtime_suspend()+0xbb8: sibling call from callable instruction with modified stack frame
  drivers/video/fbdev/omap2/omapfb/dss/dispc.o: warning: objtool: dispc_runtime_resume()+0xcc5: sibling call from callable instruction with modified stack frame

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/b6098294fd67afb69af8c47c9883d7a68bf0f8ea.1526305958.git.jpoimboe@redhat.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent fd35c88b

tools/objtool/check.c

+18 −15

Original line number	Diff line number	Diff line
		@@ -903,24 +903,24 @@ static struct rela find_switch_table(struct objtool_file file,
		{
		struct rela text_rela, rodata_rela;
		struct instruction *orig_insn = insn;
		unsigned long table_offset;

		/* case 1 & 2 */
		text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
		if (text_rela && text_rela->sym == file->rodata->sym &&
		!find_symbol_containing(file->rodata, text_rela->addend)) {

		/* case 1 */
		rodata_rela = find_rela_by_dest(file->rodata,
		text_rela->addend);
		if (rodata_rela)
		return rodata_rela;

		table_offset = text_rela->addend;
		if (text_rela->type == R_X86_64_PC32) {
		/* case 2 */
		rodata_rela = find_rela_by_dest(file->rodata,
		text_rela->addend + 4);
		table_offset += 4;
		file->ignore_unreachables = true;
		}

		rodata_rela = find_rela_by_dest(file->rodata, table_offset);
		if (!rodata_rela)
		return NULL;

		file->ignore_unreachables = true;
		return rodata_rela;
		}

		@@ -954,17 +954,20 @@ static struct rela find_switch_table(struct objtool_file file,
		if (!text_rela \|\| text_rela->sym != file->rodata->sym)
		continue;

		table_offset = text_rela->addend;
		if (text_rela->type == R_X86_64_PC32)
		table_offset += 4;

		/*
		* Make sure the .rodata address isn't associated with a
		* symbol. gcc jump tables are anonymous data.
		*/
		if (find_symbol_containing(file->rodata, text_rela->addend))
		continue;

		rodata_rela = find_rela_by_dest(file->rodata, text_rela->addend);
		if (!rodata_rela)
		if (find_symbol_containing(file->rodata, table_offset))
		continue;

		/* mov [rodata addr], %reg */
		rodata_rela = find_rela_by_dest(file->rodata, table_offset);
		if (rodata_rela)
		return rodata_rela;
		}

Admin message