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authorJosh Poimboeuf <jpoimboe@redhat.com>2017-09-20 17:24:32 -0400
committerIngo Molnar <mingo@kernel.org>2017-09-23 09:06:19 -0400
commit0d0970eef3b03ef08b19da5bc3044410731cf38f (patch)
tree3cbc6c409fce79dddb54b110a557a78dc8720086
parent4ba55e65f471d011d3ba2ac2022180ea0877d68e (diff)
objtool: Handle another GCC stack pointer adjustment bug
The kbuild bot reported the following warning with GCC 4.4 and a randconfig: net/socket.o: warning: objtool: compat_sock_ioctl()+0x1083: stack state mismatch: cfa1=7+160 cfa2=-1+0 This is caused by another GCC non-optimization, where it backs up and restores the stack pointer for no apparent reason: 2f91: 48 89 e0 mov %rsp,%rax 2f94: 4c 89 e7 mov %r12,%rdi 2f97: 4c 89 f6 mov %r14,%rsi 2f9a: ba 20 00 00 00 mov $0x20,%edx 2f9f: 48 89 c4 mov %rax,%rsp This issue would have been happily ignored before the following commit: dd88a0a0c861 ("objtool: Handle GCC stack pointer adjustment bug") But now that objtool is paying attention to such stack pointer writes to/from a register, it needs to understand them properly. In this case that means recognizing that the "mov %rsp, %rax" instruction is potentially a backup of the stack pointer. Reported-by: kbuild test robot <fengguang.wu@intel.com> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Alexander Potapenko <glider@google.com> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Dmitriy Vyukov <dvyukov@google.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Matthias Kaehlcke <mka@chromium.org> Cc: Miguel Bernal Marin <miguel.bernal.marin@linux.intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Fixes: dd88a0a0c861 ("objtool: Handle GCC stack pointer adjustment bug") Link: http://lkml.kernel.org/r/8c7aa8e9a36fbbb6655d9d8e7cea58958c912da8.1505942196.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r--tools/objtool/arch/x86/decode.c6
-rw-r--r--tools/objtool/check.c43
2 files changed, 32 insertions, 17 deletions
diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 0e8c8ec4fd4e..0f22768c0d4d 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -208,14 +208,14 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
208 break; 208 break;
209 209
210 case 0x89: 210 case 0x89:
211 if (rex == 0x48 && modrm == 0xe5) { 211 if (rex_w && !rex_r && modrm_mod == 3 && modrm_reg == 4) {
212 212
213 /* mov %rsp, %rbp */ 213 /* mov %rsp, reg */
214 *type = INSN_STACK; 214 *type = INSN_STACK;
215 op->src.type = OP_SRC_REG; 215 op->src.type = OP_SRC_REG;
216 op->src.reg = CFI_SP; 216 op->src.reg = CFI_SP;
217 op->dest.type = OP_DEST_REG; 217 op->dest.type = OP_DEST_REG;
218 op->dest.reg = CFI_BP; 218 op->dest.reg = op_to_cfi_reg[modrm_rm][rex_b];
219 break; 219 break;
220 } 220 }
221 221
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index f744617c9946..a0c518ecf085 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1203,24 +1203,39 @@ static int update_insn_state(struct instruction *insn, struct insn_state *state)
1203 switch (op->src.type) { 1203 switch (op->src.type) {
1204 1204
1205 case OP_SRC_REG: 1205 case OP_SRC_REG:
1206 if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP) { 1206 if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1207 cfa->base == CFI_SP &&
1208 regs[CFI_BP].base == CFI_CFA &&
1209 regs[CFI_BP].offset == -cfa->offset) {
1210
1211 /* mov %rsp, %rbp */
1212 cfa->base = op->dest.reg;
1213 state->bp_scratch = false;
1214 }
1207 1215
1208 if (cfa->base == CFI_SP && 1216 else if (op->src.reg == CFI_SP &&
1209 regs[CFI_BP].base == CFI_CFA && 1217 op->dest.reg == CFI_BP && state->drap) {
1210 regs[CFI_BP].offset == -cfa->offset) {
1211 1218
1212 /* mov %rsp, %rbp */ 1219 /* drap: mov %rsp, %rbp */
1213 cfa->base = op->dest.reg; 1220 regs[CFI_BP].base = CFI_BP;
1214 state->bp_scratch = false; 1221 regs[CFI_BP].offset = -state->stack_size;
1215 } 1222 state->bp_scratch = false;
1223 }
1216 1224
1217 else if (state->drap) { 1225 else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1218 1226
1219 /* drap: mov %rsp, %rbp */ 1227 /*
1220 regs[CFI_BP].base = CFI_BP; 1228 * mov %rsp, %reg
1221 regs[CFI_BP].offset = -state->stack_size; 1229 *
1222 state->bp_scratch = false; 1230 * This is needed for the rare case where GCC
1223 } 1231 * does:
1232 *
1233 * mov %rsp, %rax
1234 * ...
1235 * mov %rax, %rsp
1236 */
1237 state->vals[op->dest.reg].base = CFI_CFA;
1238 state->vals[op->dest.reg].offset = -state->stack_size;
1224 } 1239 }
1225 1240
1226 else if (op->dest.reg == cfa->base) { 1241 else if (op->dest.reg == cfa->base) {