linux-kernel - [PATCH v2 1/3] objtool/LoongArch: Decode secondary stack instruction

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Message-ID: <20240805032700.16038-2-yangtiezhu@loongson.cn>
Date: Mon,  5 Aug 2024 11:26:58 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Josh Poimboeuf <jpoimboe@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Huacai Chen <chenhuacai@...nel.org>
Cc: loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/3] objtool/LoongArch: Decode secondary stack instruction

After commit a0f7085f6a63 ("LoongArch: Add RANDOMIZE_KSTACK_OFFSET
support"), there is a new instruction "sub.d $sp, $sp, $t0" for the
secondary stack in do_syscall(), then there exists a objtool warning
"do_syscall+0x11c: return with modified stack frame" and there is no
handle_syscall() which is the previous frame of do_syscall() in the
call trace when executing the command "echo l > /proc/sysrq-trigger".

In order to solve the above issues, the first step is to decode the
secondary stack instruction "sub.d $sp, $sp, $t0".

Cc: stable@...r.kernel.org # 6.9+
Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
---
 tools/arch/loongarch/include/asm/inst.h | 12 ++++++++++++
 tools/objtool/arch/loongarch/decode.c   | 21 +++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/tools/arch/loongarch/include/asm/inst.h b/tools/arch/loongarch/include/asm/inst.h
index c25b5853181d..935b596642e2 100644
--- a/tools/arch/loongarch/include/asm/inst.h
+++ b/tools/arch/loongarch/include/asm/inst.h
@@ -51,6 +51,10 @@ enum reg2i16_op {
 	bgeu_op		= 0x1b,
 };
 
+enum reg3_op {
+	subd_op		= 0x23,
+};
+
 struct reg0i15_format {
 	unsigned int immediate : 15;
 	unsigned int opcode : 17;
@@ -96,6 +100,13 @@ struct reg2i16_format {
 	unsigned int opcode : 6;
 };
 
+struct reg3_format {
+	unsigned int rd : 5;
+	unsigned int rj : 5;
+	unsigned int rk : 5;
+	unsigned int opcode : 17;
+};
+
 union loongarch_instruction {
 	unsigned int word;
 	struct reg0i15_format	reg0i15_format;
@@ -105,6 +116,7 @@ union loongarch_instruction {
 	struct reg2i12_format	reg2i12_format;
 	struct reg2i14_format	reg2i14_format;
 	struct reg2i16_format	reg2i16_format;
+	struct reg3_format	reg3_format;
 };
 
 #define LOONGARCH_INSN_SIZE	sizeof(union loongarch_instruction)
diff --git a/tools/objtool/arch/loongarch/decode.c b/tools/objtool/arch/loongarch/decode.c
index aee479d2191c..db4dd05cdb49 100644
--- a/tools/objtool/arch/loongarch/decode.c
+++ b/tools/objtool/arch/loongarch/decode.c
@@ -272,6 +272,25 @@ static bool decode_insn_reg2i16_fomat(union loongarch_instruction inst,
 	return true;
 }
 
+static bool decode_insn_reg3_fomat(union loongarch_instruction inst,
+				   struct instruction *insn)
+{
+	switch (inst.reg3_format.opcode) {
+	case subd_op:
+		if ((inst.reg3_format.rd == CFI_SP) && (inst.reg3_format.rj == CFI_SP)) {
+			/*
+			 * sub.d sp,sp,t0
+			 * this is a rare case for the secondary stack.
+			 */
+		}
+		break;
+	default:
+		return false;
+	}
+
+	return true;
+}
+
 int arch_decode_instruction(struct objtool_file *file, const struct section *sec,
 			    unsigned long offset, unsigned int maxlen,
 			    struct instruction *insn)
@@ -303,6 +322,8 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec
 		return 0;
 	if (decode_insn_reg2i16_fomat(inst, insn))
 		return 0;
+	if (decode_insn_reg3_fomat(inst, insn))
+		return 0;
 
 	if (inst.word == 0)
 		insn->type = INSN_NOP;
-- 
2.42.0