From dd88a0a0c8615417fe6b4285769b5b772de87279 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Tue, 29 Aug 2017 12:51:03 -0500 Subject: 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 Reported-by: kbuild test robot Signed-off-by: Josh Poimboeuf Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/6a41a96884c725e7f05413bb7df40cfe824b2444.1504028945.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar --- tools/objtool/arch/x86/decode.c | 94 ++++++++++++----------------------------- 1 file changed, 26 insertions(+), 68 deletions(-) (limited to 'tools/objtool/arch/x86') 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; -- cgit v1.2.3-55-g7522