[RFC][PATCH v2 7/7] objtool,x86: Rewrite ADD/SUB/AND

From: Peter Zijlstra
Date: Thu Feb 11 2021 - 13:08:23 EST


Support sign extending and imm8 forms.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
tools/objtool/arch/x86/decode.c | 70 +++++++++++++++++++++++++++++-----------
1 file changed, 51 insertions(+), 19 deletions(-)

--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -98,13 +98,14 @@ int arch_decode_instruction(const struct
struct list_head *ops_list)
{
struct insn insn;
- int x86_64, sign;
+ int x86_64;
unsigned char op1, op2,
rex = 0, rex_b = 0, rex_r = 0, rex_w = 0, rex_x = 0,
modrm = 0, modrm_mod = 0, modrm_rm = 0, modrm_reg = 0,
sib = 0, /* sib_scale = 0, */ sib_index = 0, sib_base = 0;
struct stack_op *op = NULL;
struct symbol *sym;
+ u64 imm;

x86_64 = is_x86_64(elf);
if (x86_64 == -1)
@@ -200,12 +201,54 @@ int arch_decode_instruction(const struct
*type = INSN_JUMP_CONDITIONAL;
break;

- case 0x81:
- case 0x83:
- if (rex != 0x48)
+ case 0x80 ... 0x83:
+ /*
+ * 1000 00sw : mod OP r/m : immediate
+ *
+ * s - sign extend immediate
+ * w - imm8 / imm32
+ *
+ * OP: 000 ADD 100 AND
+ * 001 OR 101 SUB
+ * 010 ADC 110 XOR
+ * 011 SBB 111 CMP
+ */
+
+ /* 64bit only */
+ if (!rex_w)
+ break;
+
+ /* %rsp target only */
+ if (!(modrm_mod == 3 && modrm_rm == CFI_SP))
break;

- if (modrm == 0xe4) {
+ imm = insn.immediate.value;
+ if (op1 & 2) { /* sign extend */
+ if (op1 & 1) { /* imm32 */
+ imm <<= 32;
+ imm = (s64)imm >> 32;
+ } else { /* imm8 */
+ imm <<= 56;
+ imm = (s64)imm >> 56;
+ }
+ }
+
+ switch (modrm_reg & 7) {
+ case 5:
+ imm = -imm;
+ /* fallthrough */
+ case 0:
+ /* add/sub imm, %rsp */
+ ADD_OP(op) {
+ op->src.type = OP_SRC_ADD;
+ op->src.reg = CFI_SP;
+ op->src.offset = imm;
+ op->dest.type = OP_DEST_REG;
+ op->dest.reg = CFI_SP;
+ }
+ break;
+
+ case 4:
/* and imm, %rsp */
ADD_OP(op) {
op->src.type = OP_SRC_AND;
@@ -215,23 +258,12 @@ int arch_decode_instruction(const struct
op->dest.reg = CFI_SP;
}
break;
- }

- if (modrm == 0xc4)
- sign = 1;
- else if (modrm == 0xec)
- sign = -1;
- else
+ default:
+ /* WARN ? */
break;
-
- /* add/sub imm, %rsp */
- ADD_OP(op) {
- op->src.type = OP_SRC_ADD;
- op->src.reg = CFI_SP;
- op->src.offset = insn.immediate.value * sign;
- op->dest.type = OP_DEST_REG;
- op->dest.reg = CFI_SP;
}
+
break;

case 0x89: