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Subject[PATCH v2.1 2/3] objtool,x86: Additionally decode: mov %rsp, (%reg)

Subject: objtool,x86: Additionally decode: mov %rsp, (%reg)
From: Peter Zijlstra <peterz@infradead.org>
Date: Wed Feb 3 12:02:18 CET 2021

Where we already decode: mov %rsp, %reg, also decode mov %rsp, (%reg).

Nothing should match for this new stack-op.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
tools/objtool/arch/x86/decode.c | 42 ++++++++++++++++++++++++++++++++--------
1 file changed, 34 insertions(+), 8 deletions(-)

--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -222,15 +222,38 @@ int arch_decode_instruction(const struct
break;

case 0x89:
- if (rex_w && !rex_r && modrm_mod == 3 && modrm_reg == 4) {
+ if (rex_w && !rex_r && modrm_reg == 4) {

- /* mov %rsp, reg */
- ADD_OP(op) {
- op->src.type = OP_SRC_REG;
- op->src.reg = CFI_SP;
- op->dest.type = OP_DEST_REG;
- op->dest.reg = op_to_cfi_reg[modrm_rm][rex_b];
+ if (modrm_mod == 3) {
+ /* mov %rsp, reg */
+ ADD_OP(op) {
+ op->src.type = OP_SRC_REG;
+ op->src.reg = CFI_SP;
+ op->dest.type = OP_DEST_REG;
+ op->dest.reg = op_to_cfi_reg[modrm_rm][rex_b];
+ }
+ break;
+
+ } else {
+ /* skip nontrivial SIB */
+ if (modrm_rm == 4 && sib != 0x24)
+ break;
+
+ /* skip RIP relative displacement */
+ if (modrm_rm == 5 && modrm_mod == 0)
+ break;
+
+ /* mov %rsp, disp(%reg) */
+ ADD_OP(op) {
+ op->src.type = OP_SRC_REG;
+ op->src.reg = CFI_SP;
+ op->dest.type = OP_DEST_REG_INDIRECT;
+ op->dest.reg = op_to_cfi_reg[modrm_rm][rex_b];
+ op->dest.offset = insn.displacement.value;
+ }
+ break;
}
+
break;
}

@@ -259,8 +282,10 @@ int arch_decode_instruction(const struct
op->dest.reg = CFI_BP;
op->dest.offset = insn.displacement.value;
}
+ break;
+ }

- } else if (rex_w && !rex_b && modrm_rm == 4 && sib == 0x24) {
+ if (rex_w && !rex_b && modrm_rm == 4 && sib == 0x24) {

/* mov reg, disp(%rsp) */
ADD_OP(op) {
@@ -270,6 +295,7 @@ int arch_decode_instruction(const struct
op->dest.reg = CFI_SP;
op->dest.offset = insn.displacement.value;
}
+ break;
}

break;
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