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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
parent499934898fcd15e4337dc858be6c09cd9fd74e85 (diff)
downloadlinux-stericsson-dd88a0a0c8615417fe6b4285769b5b772de87279.tar.gz
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')
-rw-r--r--tools/objtool/arch/x86/decode.c94
-rw-r--r--tools/objtool/cfi.h2
-rw-r--r--tools/objtool/check.c81
-rw-r--r--tools/objtool/check.h1
4 files changed, 88 insertions, 90 deletions
diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 7841e5d31973..0e8c8ec4fd4e 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -86,8 +86,8 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
struct insn insn;
int x86_64, sign;
unsigned char op1, op2, rex = 0, rex_b = 0, rex_r = 0, rex_w = 0,
- modrm = 0, modrm_mod = 0, modrm_rm = 0, modrm_reg = 0,
- sib = 0;
+ rex_x = 0, modrm = 0, modrm_mod = 0, modrm_rm = 0,
+ modrm_reg = 0, sib = 0;
x86_64 = is_x86_64(elf);
if (x86_64 == -1)
@@ -114,6 +114,7 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
rex = insn.rex_prefix.bytes[0];
rex_w = X86_REX_W(rex) >> 3;
rex_r = X86_REX_R(rex) >> 2;
+ rex_x = X86_REX_X(rex) >> 1;
rex_b = X86_REX_B(rex);
}
@@ -217,6 +218,18 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
op->dest.reg = CFI_BP;
break;
}
+
+ if (rex_w && !rex_b && modrm_mod == 3 && modrm_rm == 4) {
+
+ /* mov reg, %rsp */
+ *type = INSN_STACK;
+ op->src.type = OP_SRC_REG;
+ op->src.reg = op_to_cfi_reg[modrm_reg][rex_r];
+ op->dest.type = OP_DEST_REG;
+ op->dest.reg = CFI_SP;
+ break;
+ }
+
/* fallthrough */
case 0x88:
if (!rex_b &&
@@ -269,80 +282,28 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
break;
case 0x8d:
- if (rex == 0x48 && modrm == 0x65) {
+ if (sib == 0x24 && rex_w && !rex_b && !rex_x) {
- /* lea disp(%rbp), %rsp */
+ /* lea disp(%rsp), reg */
*type = INSN_STACK;
op->src.type = OP_SRC_ADD;
- op->src.reg = CFI_BP;
+ op->src.reg = CFI_SP;
op->src.offset = insn.displacement.value;
op->dest.type = OP_DEST_REG;
- op->dest.reg = CFI_SP;
- break;
- }
+ op->dest.reg = op_to_cfi_reg[modrm_reg][rex_r];
- if (rex == 0x48 && (modrm == 0xa4 || modrm == 0x64) &&
- sib == 0x24) {
+ } else if (rex == 0x48 && modrm == 0x65) {
- /* lea disp(%rsp), %rsp */
+ /* lea disp(%rbp), %rsp */
*type = INSN_STACK;
op->src.type = OP_SRC_ADD;
- op->src.reg = CFI_SP;
+ op->src.reg = CFI_BP;
op->src.offset = insn.displacement.value;
op->dest.type = OP_DEST_REG;
op->dest.reg = CFI_SP;
- break;
- }
- if (rex == 0x48 && modrm == 0x2c && sib == 0x24) {
-
- /* lea (%rsp), %rbp */
- *type = INSN_STACK;
- op->src.type = OP_SRC_REG;
- op->src.reg = CFI_SP;
- op->dest.type = OP_DEST_REG;
- op->dest.reg = CFI_BP;
- break;
- }
-
- if (rex == 0x4c && modrm == 0x54 && sib == 0x24 &&
- insn.displacement.value == 8) {
-
- /*
- * lea 0x8(%rsp), %r10
- *
- * Here r10 is the "drap" pointer, used as a stack
- * pointer helper when the stack gets realigned.
- */
- *type = INSN_STACK;
- op->src.type = OP_SRC_ADD;
- op->src.reg = CFI_SP;
- op->src.offset = 8;
- op->dest.type = OP_DEST_REG;
- op->dest.reg = CFI_R10;
- break;
- }
-
- if (rex == 0x4c && modrm == 0x6c && sib == 0x24 &&
- insn.displacement.value == 16) {
-
- /*
- * lea 0x10(%rsp), %r13
- *
- * Here r13 is the "drap" pointer, used as a stack
- * pointer helper when the stack gets realigned.
- */
- *type = INSN_STACK;
- op->src.type = OP_SRC_ADD;
- op->src.reg = CFI_SP;
- op->src.offset = 16;
- op->dest.type = OP_DEST_REG;
- op->dest.reg = CFI_R13;
- break;
- }
-
- if (rex == 0x49 && modrm == 0x62 &&
- insn.displacement.value == -8) {
+ } else if (rex == 0x49 && modrm == 0x62 &&
+ insn.displacement.value == -8) {
/*
* lea -0x8(%r10), %rsp
@@ -356,11 +317,9 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
op->src.offset = -8;
op->dest.type = OP_DEST_REG;
op->dest.reg = CFI_SP;
- break;
- }
- if (rex == 0x49 && modrm == 0x65 &&
- insn.displacement.value == -16) {
+ } else if (rex == 0x49 && modrm == 0x65 &&
+ insn.displacement.value == -16) {
/*
* lea -0x10(%r13), %rsp
@@ -374,7 +333,6 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
op->src.offset = -16;
op->dest.type = OP_DEST_REG;
op->dest.reg = CFI_SP;
- break;
}
break;
diff --git a/tools/objtool/cfi.h b/tools/objtool/cfi.h
index 443ab2c69992..2fe883c665c7 100644
--- a/tools/objtool/cfi.h
+++ b/tools/objtool/cfi.h
@@ -40,7 +40,7 @@
#define CFI_R14 14
#define CFI_R15 15
#define CFI_RA 16
-#define CFI_NUM_REGS 17
+#define CFI_NUM_REGS 17
struct cfi_reg {
int base;
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;
}
diff --git a/tools/objtool/check.h b/tools/objtool/check.h
index 9f113016bf8c..47d9ea70a83d 100644
--- a/tools/objtool/check.h
+++ b/tools/objtool/check.h
@@ -33,6 +33,7 @@ struct insn_state {
bool bp_scratch;
bool drap;
int drap_reg, drap_offset;
+ struct cfi_reg vals[CFI_NUM_REGS];
};
struct instruction {