linux-kernel - [RFC PATCH v2 07/17] objtool: Store instruction disassembly result

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Message-ID: <20250619145659.1377970-8-alexandre.chartre@oracle.com>
Date: Thu, 19 Jun 2025 16:56:49 +0200
From: Alexandre Chartre <alexandre.chartre@...cle.com>
To: linux-kernel@...r.kernel.org, mingo@...nel.org, jpoimboe@...nel.org,
        peterz@...radead.org
Cc: alexandre.chartre@...cle.com
Subject: [RFC PATCH v2 07/17] objtool: Store instruction disassembly result

When disassembling an instruction store the result instead of directly
printing it.

Signed-off-by: Alexandre Chartre <alexandre.chartre@...cle.com>
---
 tools/objtool/disas.c | 78 +++++++++++++++++++++++++++++++++++++++----
 1 file changed, 72 insertions(+), 6 deletions(-)

diff --git a/tools/objtool/disas.c b/tools/objtool/disas.c
index 91d23f7518e3..fbec062f40eb 100644
--- a/tools/objtool/disas.c
+++ b/tools/objtool/disas.c
@@ -12,9 +12,16 @@
 #include <linux/string.h>
 #include <tools/dis-asm-compat.h>
 
+/*
+ * Size of the buffer for storing the result of disassembling
+ * a single instruction.
+ */
+#define DISAS_RESULT_SIZE	1024
+
 struct disas_context {
 	struct objtool_file *file;
 	struct instruction *insn;
+	char result[DISAS_RESULT_SIZE];
 	disassembler_ftype disassembler;
 	struct disassemble_info info;
 };
@@ -22,6 +29,60 @@ struct disas_context {
 #define DINFO_FPRINTF(dinfo, ...)	\
 	((*(dinfo)->fprintf_func)((dinfo)->stream, __VA_ARGS__))
 
+
+static int disas_result_fprintf(struct disas_context *dctx,
+				const char *fmt, va_list ap)
+{
+	char *buf = dctx->result;
+	size_t avail, len;
+
+	len = strlen(buf);
+	if (len >= DISAS_RESULT_SIZE - 1) {
+		WARN_FUNC(dctx->insn->sec, dctx->insn->offset,
+			  "disassembly buffer is full");
+		return -1;
+	}
+	avail = DISAS_RESULT_SIZE - len;
+
+	len = vsnprintf(buf + len, avail, fmt, ap);
+	if (len < 0 || len >= avail) {
+		WARN_FUNC(dctx->insn->sec, dctx->insn->offset,
+			  "disassembly buffer is truncated");
+		return -1;
+	}
+
+	return 0;
+}
+
+static int disas_fprintf(void *stream, const char *fmt, ...)
+{
+	va_list arg;
+	int rv;
+
+	va_start(arg, fmt);
+	rv = disas_result_fprintf(stream, fmt, arg);
+	va_end(arg);
+
+	return rv;
+}
+
+/*
+ * For init_disassemble_info_compat().
+ */
+static int disas_fprintf_styled(void *stream,
+				enum disassembler_style style,
+				const char *fmt, ...)
+{
+	va_list arg;
+	int rv;
+
+	va_start(arg, fmt);
+	rv = disas_result_fprintf(stream, fmt, arg);
+	va_end(arg);
+
+	return rv;
+}
+
 static void disas_print_address(bfd_vma addr, struct disassemble_info *dinfo)
 {
 	struct disas_context *dctx = dinfo->application_data;
@@ -147,9 +208,8 @@ struct disas_context *disas_context_create(struct objtool_file *file)
 	dctx->file = file;
 	dinfo = &dctx->info;
 
-	init_disassemble_info_compat(dinfo, stdout,
-				     (fprintf_ftype)fprintf,
-				     fprintf_styled);
+	init_disassemble_info_compat(dinfo, dctx,
+				     disas_fprintf, disas_fprintf_styled);
 
 	dinfo->read_memory_func = buffer_read_memory;
 	dinfo->print_address_func = disas_print_address;
@@ -196,6 +256,11 @@ void disas_context_destroy(struct disas_context *dctx)
 	free(dctx);
 }
 
+static char *disas_result(struct disas_context *dctx)
+{
+	return dctx->result;
+}
+
 /*
  * Disassemble a single instruction. Return the size of the instruction.
  */
@@ -206,6 +271,7 @@ static size_t disas_insn(struct disas_context *dctx,
 	struct disassemble_info *dinfo = &dctx->info;
 
 	dctx->insn = insn;
+	dctx->result[0] = '\0';
 
 	/*
 	 * Set the disassembler buffer to read data from the section
@@ -229,10 +295,10 @@ static void disas_func(struct disas_context *dctx, struct symbol *func)
 	printf("%s:\n", func->name);
 	sym_for_each_insn(dctx->file, func, insn) {
 		addr = insn->offset;
-		printf(" %6lx:  %s+0x%-6lx      ",
-		       addr, func->name, addr - func->offset);
 		disas_insn(dctx, insn);
-		printf("\n");
+		printf(" %6lx:  %s+0x%-6lx      %s\n",
+		       addr, func->name, addr - func->offset,
+		       disas_result(dctx));
 	}
 	printf("\n");
 }
-- 
2.43.5