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authorJosh Poimboeuf <jpoimboe@redhat.com>2017-07-27 15:56:53 -0500
committerIngo Molnar <mingo@kernel.org>2017-07-28 08:33:32 +0200
commit649ea4d5a624f061a111b1f1cb0e47cfdc3ac21b (patch)
tree1ca57938fb1f6cef077da35e6f1114e0181c3088 /tools/objtool
parenta632375764aa25c97b78beb56c71b0ba59d1cf83 (diff)
downloadlinux-stericsson-649ea4d5a624f061a111b1f1cb0e47cfdc3ac21b.tar.gz
objtool: Assume unannotated UD2 instructions are dead ends
Arnd reported some false positive warnings with GCC 7: drivers/hid/wacom_wac.o: warning: objtool: wacom_bpt3_touch()+0x2a5: stack state mismatch: cfa1=7+8 cfa2=6+16 drivers/iio/adc/vf610_adc.o: warning: objtool: vf610_adc_calculate_rates() falls through to next function vf610_adc_sample_set() drivers/pwm/pwm-hibvt.o: warning: objtool: hibvt_pwm_get_state() falls through to next function hibvt_pwm_remove() drivers/pwm/pwm-mediatek.o: warning: objtool: mtk_pwm_config() falls through to next function mtk_pwm_enable() drivers/spi/spi-bcm2835.o: warning: objtool: .text: unexpected end of section drivers/spi/spi-bcm2835aux.o: warning: objtool: .text: unexpected end of section drivers/watchdog/digicolor_wdt.o: warning: objtool: dc_wdt_get_timeleft() falls through to next function dc_wdt_restart() When GCC 7 detects a potential divide-by-zero condition, it sometimes inserts a UD2 instruction for the case where the divisor is zero, instead of letting the hardware trap on the divide instruction. Objtool doesn't consider UD2 to be fatal unless it's annotated with unreachable(). So it considers the GCC-generated UD2 to be non-fatal, and it tries to follow the control flow past the UD2 and gets confused. Previously, objtool *did* assume UD2 was always a dead end. That changed with the following commit: d1091c7fa3d5 ("objtool: Improve detection of BUG() and other dead ends") The motivation behind that change was that Peter was planning on using UD2 for __WARN(), which is *not* a dead end. However, it turns out that some emulators rely on UD2 being fatal, so he ended up using 'ud0' instead: 9a93848fe787 ("x86/debug: Implement __WARN() using UD0") For GCC 4.5+, it should be safe to go back to the previous assumption that UD2 is fatal, even when it's not annotated with unreachable(). But for pre-4.5 versions of GCC, the unreachable() macro isn't supported, so such cases of UD2 need to be explicitly annotated as reachable. Reported-by: Arnd Bergmann <arnd@arndb.de> 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> Fixes: d1091c7fa3d5 ("objtool: Improve detection of BUG() and other dead ends") Link: http://lkml.kernel.org/r/e57fa9dfede25f79487da8126ee9cdf7b856db65.1501188854.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'tools/objtool')
-rw-r--r--tools/objtool/arch.h5
-rw-r--r--tools/objtool/arch/x86/decode.c17
-rw-r--r--tools/objtool/check.c57
3 files changed, 70 insertions, 9 deletions
diff --git a/tools/objtool/arch.h b/tools/objtool/arch.h
index 21aeca874edb..b0d7dc3d71b5 100644
--- a/tools/objtool/arch.h
+++ b/tools/objtool/arch.h
@@ -31,8 +31,9 @@
#define INSN_RETURN 6
#define INSN_CONTEXT_SWITCH 7
#define INSN_STACK 8
-#define INSN_NOP 9
-#define INSN_OTHER 10
+#define INSN_BUG 9
+#define INSN_NOP 10
+#define INSN_OTHER 11
#define INSN_LAST INSN_OTHER
enum op_dest_type {
diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index a36c2eba64e7..e4b400b67e41 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -382,20 +382,27 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
case 0x0f:
- if (op2 >= 0x80 && op2 <= 0x8f)
+ if (op2 >= 0x80 && op2 <= 0x8f) {
+
*type = INSN_JUMP_CONDITIONAL;
- else if (op2 == 0x05 || op2 == 0x07 || op2 == 0x34 ||
- op2 == 0x35)
+
+ } else if (op2 == 0x05 || op2 == 0x07 || op2 == 0x34 ||
+ op2 == 0x35) {
/* sysenter, sysret */
*type = INSN_CONTEXT_SWITCH;
- else if (op2 == 0x0d || op2 == 0x1f)
+ } else if (op2 == 0x0b || op2 == 0xb9) {
+
+ /* ud2 */
+ *type = INSN_BUG;
+
+ } else if (op2 == 0x0d || op2 == 0x1f) {
/* nopl/nopw */
*type = INSN_NOP;
- else if (op2 == 0xa0 || op2 == 0xa8) {
+ } else if (op2 == 0xa0 || op2 == 0xa8) {
/* push fs/gs */
*type = INSN_STACK;
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 3436a942b606..d07bf4a62b45 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -296,7 +296,7 @@ static int decode_instructions(struct objtool_file *file)
}
/*
- * Find all uses of the unreachable() macro, which are code path dead ends.
+ * Mark "ud2" instructions and manually annotated dead ends.
*/
static int add_dead_ends(struct objtool_file *file)
{
@@ -305,9 +305,20 @@ static int add_dead_ends(struct objtool_file *file)
struct instruction *insn;
bool found;
+ /*
+ * By default, "ud2" is a dead end unless otherwise annotated, because
+ * GCC 7 inserts it for certain divide-by-zero cases.
+ */
+ for_each_insn(file, insn)
+ if (insn->type == INSN_BUG)
+ insn->dead_end = true;
+
+ /*
+ * Check for manually annotated dead ends.
+ */
sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
if (!sec)
- return 0;
+ goto reachable;
list_for_each_entry(rela, &sec->rela_list, list) {
if (rela->sym->type != STT_SECTION) {
@@ -340,6 +351,48 @@ static int add_dead_ends(struct objtool_file *file)
insn->dead_end = true;
}
+reachable:
+ /*
+ * These manually annotated reachable checks are needed for GCC 4.4,
+ * where the Linux unreachable() macro isn't supported. In that case
+ * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
+ * not a dead end.
+ */
+ sec = find_section_by_name(file->elf, ".rela.discard.reachable");
+ if (!sec)
+ return 0;
+
+ list_for_each_entry(rela, &sec->rela_list, list) {
+ if (rela->sym->type != STT_SECTION) {
+ WARN("unexpected relocation symbol type in %s", sec->name);
+ return -1;
+ }
+ insn = find_insn(file, rela->sym->sec, rela->addend);
+ if (insn)
+ insn = list_prev_entry(insn, list);
+ else if (rela->addend == rela->sym->sec->len) {
+ found = false;
+ list_for_each_entry_reverse(insn, &file->insn_list, list) {
+ if (insn->sec == rela->sym->sec) {
+ found = true;
+ break;
+ }
+ }
+
+ if (!found) {
+ WARN("can't find reachable insn at %s+0x%x",
+ rela->sym->sec->name, rela->addend);
+ return -1;
+ }
+ } else {
+ WARN("can't find reachable insn at %s+0x%x",
+ rela->sym->sec->name, rela->addend);
+ return -1;
+ }
+
+ insn->dead_end = false;
+ }
+
return 0;
}