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authorJosh Poimboeuf <jpoimboe@redhat.com>2020-04-01 13:23:25 -0500
committerBorislav Petkov <bp@suse.de>2020-04-14 11:55:09 +0200
commitbd841d6154f5f41f8a32d3c1b0bc229e326e640a (patch)
tree6349f1956da0f00695f145f48a801496232cc3bf /tools
parent8f3d9f354286745c751374f5f1fcafee6b3f3136 (diff)
objtool: Fix CONFIG_UBSAN_TRAP unreachable warnings
CONFIG_UBSAN_TRAP causes GCC to emit a UD2 whenever it encounters an unreachable code path. This includes __builtin_unreachable(). Because the BUG() macro uses __builtin_unreachable() after it emits its own UD2, this results in a double UD2. In this case objtool rightfully detects that the second UD2 is unreachable: init/main.o: warning: objtool: repair_env_string()+0x1c8: unreachable instruction We weren't able to figure out a way to get rid of the double UD2s, so just silence the warning. Reported-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Signed-off-by: Borislav Petkov <bp@suse.de> Reviewed-by: Kees Cook <keescook@chromium.org> Reviewed-by: Miroslav Benes <mbenes@suse.cz> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/6653ad73c6b59c049211bd7c11ed3809c20ee9f5.1585761021.git.jpoimboe@redhat.com
Diffstat (limited to 'tools')
-rw-r--r--tools/objtool/check.c17
1 files changed, 15 insertions, 2 deletions
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 8dd01f986fbb..481132539384 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2364,14 +2364,27 @@ static bool ignore_unreachable_insn(struct instruction *insn)
!strcmp(insn->sec->name, ".altinstr_aux"))
return true;
+ if (!insn->func)
+ return false;
+
+ /*
+ * CONFIG_UBSAN_TRAP inserts a UD2 when it sees
+ * __builtin_unreachable(). The BUG() macro has an unreachable() after
+ * the UD2, which causes GCC's undefined trap logic to emit another UD2
+ * (or occasionally a JMP to UD2).
+ */
+ if (list_prev_entry(insn, list)->dead_end &&
+ (insn->type == INSN_BUG ||
+ (insn->type == INSN_JUMP_UNCONDITIONAL &&
+ insn->jump_dest && insn->jump_dest->type == INSN_BUG)))
+ return true;
+
/*
* Check if this (or a subsequent) instruction is related to
* CONFIG_UBSAN or CONFIG_KASAN.
*
* End the search at 5 instructions to avoid going into the weeds.
*/
- if (!insn->func)
- return false;
for (i = 0; i < 5; i++) {
if (is_kasan_insn(insn) || is_ubsan_insn(insn))