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>

1 files changed, 18 insertions, 15 deletions

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 9bb04fddd3c8..f4bbce838433 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -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 */
+                        table_offset += 4;
+                        file->ignore_unreachables = true;
+                }
 
-                /* case 2 */
-                rodata_rela = find_rela_by_dest(file->rodata,
-                                                text_rela->addend + 4);
+                rodata_rela = find_rela_by_dest(file->rodata, table_offset);
                 if (!rodata_rela)
                         return NULL;
 
-                file->ignore_unreachables = true;
                 return rodata_rela;
         }
 
@@ -954,18 +954,21 @@ 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;
 
-                return rodata_rela;
+                /* mov [rodata addr], %reg */
+                rodata_rela = find_rela_by_dest(file->rodata, table_offset);
+                if (rodata_rela)
+                        return rodata_rela;
         }
 
         return NULL;