[tip: objtool/core] objtool,x86: Simplify register decode

From: tip-bot2 for Peter Zijlstra
Date: Sat Mar 06 2021 - 06:49:27 EST

The following commit has been merged into the objtool/core branch of tip:

Commit-ID: 16ef7f159c503c7befec7018ee0e82fdc311721e
Gitweb: https://git.kernel.org/tip/16ef7f159c503c7befec7018ee0e82fdc311721e
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Tue, 09 Feb 2021 19:59:43 +01:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Sat, 06 Mar 2021 12:44:23 +01:00

objtool,x86: Simplify register decode

Since the CFI_reg number now matches the instruction encoding order do
away with the op_to_cfi_reg[] and use direct assignment.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Tested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20210211173627.362004522@xxxxxxxxxxxxx
---
tools/objtool/arch/x86/decode.c | 79 +++++++++++++++-----------------
1 file changed, 39 insertions(+), 40 deletions(-)

diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 47b9acf..5ce7dc4 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -17,17 +17,6 @@
#include <objtool/arch.h>
#include <objtool/warn.h>

-static unsigned char op_to_cfi_reg[][2] = {
- {CFI_AX, CFI_R8},
- {CFI_CX, CFI_R9},
- {CFI_DX, CFI_R10},
- {CFI_BX, CFI_R11},
- {CFI_SP, CFI_R12},
- {CFI_BP, CFI_R13},
- {CFI_SI, CFI_R14},
- {CFI_DI, CFI_R15},
-};
-
static int is_x86_64(const struct elf *elf)
{
switch (elf->ehdr.e_machine) {
@@ -94,7 +83,7 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,
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 = 0 /* , sib_scale = 0, sib_index = 0, sib_base = 0 */;
struct stack_op *op = NULL;
struct symbol *sym;

@@ -130,23 +119,29 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,
if (insn.modrm.nbytes) {
modrm = insn.modrm.bytes[0];
modrm_mod = X86_MODRM_MOD(modrm);
- modrm_reg = X86_MODRM_REG(modrm);
- modrm_rm = X86_MODRM_RM(modrm);
+ modrm_reg = X86_MODRM_REG(modrm) + 8*rex_r;
+ modrm_rm = X86_MODRM_RM(modrm) + 8*rex_b;
}

- if (insn.sib.nbytes)
+ if (insn.sib.nbytes) {
sib = insn.sib.bytes[0];
+ /*
+ sib_scale = X86_SIB_SCALE(sib);
+ sib_index = X86_SIB_INDEX(sib) + 8*rex_x;
+ sib_base = X86_SIB_BASE(sib) + 8*rex_b;
+ */
+ }

switch (op1) {

case 0x1:
case 0x29:
- if (rex_w && !rex_b && modrm_mod == 3 && modrm_rm == 4) {
+ if (rex_w && modrm_mod == 3 && modrm_rm == CFI_SP) {

/* add/sub reg, %rsp */
ADD_OP(op) {
op->src.type = OP_SRC_ADD;
- op->src.reg = op_to_cfi_reg[modrm_reg][rex_r];
+ op->src.reg = modrm_reg;
op->dest.type = OP_DEST_REG;
op->dest.reg = CFI_SP;
}
@@ -158,7 +153,7 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,
/* push reg */
ADD_OP(op) {
op->src.type = OP_SRC_REG;
- op->src.reg = op_to_cfi_reg[op1 & 0x7][rex_b];
+ op->src.reg = (op1 & 0x7) + 8*rex_b;
op->dest.type = OP_DEST_PUSH;
}

@@ -170,7 +165,7 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,
ADD_OP(op) {
op->src.type = OP_SRC_POP;
op->dest.type = OP_DEST_REG;
- op->dest.reg = op_to_cfi_reg[op1 & 0x7][rex_b];
+ op->dest.reg = (op1 & 0x7) + 8*rex_b;
}

break;
@@ -223,7 +218,7 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,
break;

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

if (modrm_mod == 3) {
/* mov %rsp, reg */
@@ -231,17 +226,17 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,
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];
+ op->dest.reg = modrm_rm;
}
break;

} else {
/* skip nontrivial SIB */
- if (modrm_rm == 4 && !(sib == 0x24 && rex_b == rex_x))
+ if ((modrm_rm & 7) == 4 && !(sib == 0x24 && rex_b == rex_x))
break;

/* skip RIP relative displacement */
- if (modrm_rm == 5 && modrm_mod == 0)
+ if ((modrm_rm & 7) == 5 && modrm_mod == 0)
break;

/* mov %rsp, disp(%reg) */
@@ -249,7 +244,7 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,
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.reg = modrm_rm;
op->dest.offset = insn.displacement.value;
}
break;
@@ -258,12 +253,12 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,
break;
}

- if (rex_w && !rex_b && modrm_mod == 3 && modrm_rm == 4) {
+ if (rex_w && modrm_mod == 3 && modrm_rm == CFI_SP) {

/* mov reg, %rsp */
ADD_OP(op) {
op->src.type = OP_SRC_REG;
- op->src.reg = op_to_cfi_reg[modrm_reg][rex_r];
+ op->src.reg = modrm_reg;
op->dest.type = OP_DEST_REG;
op->dest.reg = CFI_SP;
}
@@ -272,13 +267,12 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,

/* fallthrough */
case 0x88:
- if (!rex_b &&
- (modrm_mod == 1 || modrm_mod == 2) && modrm_rm == 5) {
+ if ((modrm_mod == 1 || modrm_mod == 2) && modrm_rm == CFI_BP) {

/* mov reg, disp(%rbp) */
ADD_OP(op) {
op->src.type = OP_SRC_REG;
- op->src.reg = op_to_cfi_reg[modrm_reg][rex_r];
+ op->src.reg = modrm_reg;
op->dest.type = OP_DEST_REG_INDIRECT;
op->dest.reg = CFI_BP;
op->dest.offset = insn.displacement.value;
@@ -286,12 +280,12 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,
break;
}

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

/* mov reg, disp(%rsp) */
ADD_OP(op) {
op->src.type = OP_SRC_REG;
- op->src.reg = op_to_cfi_reg[modrm_reg][rex_r];
+ op->src.reg = modrm_reg;
op->dest.type = OP_DEST_REG_INDIRECT;
op->dest.reg = CFI_SP;
op->dest.offset = insn.displacement.value;
@@ -302,7 +296,10 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,
break;

case 0x8b:
- if (rex_w && !rex_b && modrm_mod == 1 && modrm_rm == 5) {
+ if (!rex_w)
+ break;
+
+ if (modrm_mod == 1 && modrm_rm == CFI_BP) {

/* mov disp(%rbp), reg */
ADD_OP(op) {
@@ -310,11 +307,12 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,
op->src.reg = CFI_BP;
op->src.offset = insn.displacement.value;
op->dest.type = OP_DEST_REG;
- op->dest.reg = op_to_cfi_reg[modrm_reg][rex_r];
+ op->dest.reg = modrm_reg;
}
+ break;
+ }

- } else if (rex_w && !rex_b && sib == 0x24 &&
- modrm_mod != 3 && modrm_rm == 4) {
+ if (modrm_mod != 3 && modrm_rm == CFI_SP && sib == 0x24) {

/* mov disp(%rsp), reg */
ADD_OP(op) {
@@ -322,8 +320,9 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,
op->src.reg = CFI_SP;
op->src.offset = insn.displacement.value;
op->dest.type = OP_DEST_REG;
- op->dest.reg = op_to_cfi_reg[modrm_reg][rex_r];
+ op->dest.reg = modrm_reg;
}
+ break;
}

break;
@@ -339,11 +338,11 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,
break;

/* skip nontrivial SIB */
- if (modrm_rm == 4 && !(sib == 0x24 && rex_b == rex_x))
+ if ((modrm_rm & 7) == 4 && !(sib == 0x24 && rex_b == rex_x))
break;

/* skip RIP relative displacement */
- if (modrm_rm == 5 && modrm_mod == 0)
+ if ((modrm_rm & 7) == 5 && modrm_mod == 0)
break;

/* lea disp(%src), %dst */
@@ -356,9 +355,9 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,
/* lea disp(%src), %dst */
op->src.type = OP_SRC_ADD;
}
- op->src.reg = op_to_cfi_reg[modrm_rm][rex_b];
+ op->src.reg = modrm_rm;
op->dest.type = OP_DEST_REG;
- op->dest.reg = op_to_cfi_reg[modrm_reg][rex_r];
+ op->dest.reg = modrm_reg;
}
break;