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

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

Commit-ID:     9d5a2c2caa10fc135d7020e76baa6a17c52e608f
Gitweb:        https://git.kernel.org/tip/9d5a2c2caa10fc135d7020e76baa6a17c52e608f
Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate:    Tue, 09 Feb 2021 19:59:43 +01:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Wed, 03 Mar 2021 09:38:30 +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>
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;
 



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