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authorJosh Poimboeuf <jpoimboe@redhat.com>2017-08-29 12:51:03 -0500
committerIngo Molnar <mingo@kernel.org>2017-08-30 10:48:41 +0200
commitdd88a0a0c8615417fe6b4285769b5b772de87279 (patch)
tree3ec72a80a155dff0949ced1b01510685450b0496 /tools/objtool/check.c
parent499934898fcd15e4337dc858be6c09cd9fd74e85 (diff)
objtool: Handle GCC stack pointer adjustment bug
Arnd Bergmann reported the following warning with GCC 7.1.1: fs/fs_pin.o: warning: objtool: pin_kill()+0x139: stack state mismatch: cfa1=7+88 cfa2=7+96 And the kbuild robot reported the following warnings with GCC 5.4.1: fs/fs_pin.o: warning: objtool: pin_kill()+0x182: return with modified stack frame fs/quota/dquot.o: warning: objtool: dquot_alloc_inode()+0x140: stack state mismatch: cfa1=7+120 cfa2=7+128 fs/quota/dquot.o: warning: objtool: dquot_free_inode()+0x11a: stack state mismatch: cfa1=7+112 cfa2=7+120 Those warnings are caused by an unusual GCC non-optimization where it uses an intermediate register to adjust the stack pointer. It does: lea 0x8(%rsp), %rcx ... mov %rcx, %rsp Instead of the obvious: add $0x8, %rsp It makes no sense to use an intermediate register, so I opened a GCC bug to track it: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81813 But it's not exactly a high-priority bug and it looks like we'll be stuck with this issue for a while. So for now we have to track register values when they're loaded with stack pointer offsets. This is kind of a big workaround for a tiny problem, but c'est la vie. I hope to eventually create a GCC plugin to implement a big chunk of objtool's functionality. Hopefully at that point we'll be able to remove of a lot of these GCC-isms from the objtool code. Reported-by: Arnd Bergmann <arnd@arndb.de> Reported-by: kbuild test robot <fengguang.wu@intel.com> 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/6a41a96884c725e7f05413bb7df40cfe824b2444.1504028945.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'tools/objtool/check.c')
-rw-r--r--tools/objtool/check.c81
1 files changed, 60 insertions, 21 deletions
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 3dffeb944523..f744617c9946 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -218,8 +218,10 @@ static void clear_insn_state(struct insn_state *state)
memset(state, 0, sizeof(*state));
state->cfa.base = CFI_UNDEFINED;
- for (i = 0; i < CFI_NUM_REGS; i++)
+ for (i = 0; i < CFI_NUM_REGS; i++) {
state->regs[i].base = CFI_UNDEFINED;
+ state->vals[i].base = CFI_UNDEFINED;
+ }
state->drap_reg = CFI_UNDEFINED;
state->drap_offset = -1;
}
@@ -1201,24 +1203,47 @@ static int update_insn_state(struct instruction *insn, struct insn_state *state)
switch (op->src.type) {
case OP_SRC_REG:
- if (cfa->base == op->src.reg && cfa->base == CFI_SP &&
- op->dest.reg == CFI_BP && regs[CFI_BP].base == CFI_CFA &&
- regs[CFI_BP].offset == -cfa->offset) {
-
- /* mov %rsp, %rbp */
- cfa->base = op->dest.reg;
- state->bp_scratch = false;
- } else if (state->drap) {
-
- /* drap: mov %rsp, %rbp */
- regs[CFI_BP].base = CFI_BP;
- regs[CFI_BP].offset = -state->stack_size;
- state->bp_scratch = false;
- } else if (!no_fp) {
-
- WARN_FUNC("unknown stack-related register move",
- insn->sec, insn->offset);
- return -1;
+ if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP) {
+
+ if (cfa->base == CFI_SP &&
+ regs[CFI_BP].base == CFI_CFA &&
+ regs[CFI_BP].offset == -cfa->offset) {
+
+ /* mov %rsp, %rbp */
+ cfa->base = op->dest.reg;
+ state->bp_scratch = false;
+ }
+
+ else if (state->drap) {
+
+ /* drap: mov %rsp, %rbp */
+ regs[CFI_BP].base = CFI_BP;
+ regs[CFI_BP].offset = -state->stack_size;
+ state->bp_scratch = false;
+ }
+ }
+
+ else if (op->dest.reg == cfa->base) {
+
+ /* mov %reg, %rsp */
+ if (cfa->base == CFI_SP &&
+ state->vals[op->src.reg].base == CFI_CFA) {
+
+ /*
+ * This is needed for the rare case
+ * where GCC does something dumb like:
+ *
+ * lea 0x8(%rsp), %rcx
+ * ...
+ * mov %rcx, %rsp
+ */
+ cfa->offset = -state->vals[op->src.reg].offset;
+ state->stack_size = cfa->offset;
+
+ } else {
+ cfa->base = CFI_UNDEFINED;
+ cfa->offset = 0;
+ }
}
break;
@@ -1240,11 +1265,25 @@ static int update_insn_state(struct instruction *insn, struct insn_state *state)
break;
}
- if (op->dest.reg != CFI_BP && op->src.reg == CFI_SP &&
- cfa->base == CFI_SP) {
+ if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
/* drap: lea disp(%rsp), %drap */
state->drap_reg = op->dest.reg;
+
+ /*
+ * lea disp(%rsp), %reg
+ *
+ * This is needed for the rare case where GCC
+ * does something dumb like:
+ *
+ * lea 0x8(%rsp), %rcx
+ * ...
+ * mov %rcx, %rsp
+ */
+ state->vals[op->dest.reg].base = CFI_CFA;
+ state->vals[op->dest.reg].offset = \
+ -state->stack_size + op->src.offset;
+
break;
}