[PATCH 12/13] objtool: Create backup on error and print args

Josh Poimboeuf posted 13 patches 9 months, 1 week ago
[PATCH 12/13] objtool: Create backup on error and print args
Posted by Josh Poimboeuf 9 months, 1 week ago
Recreating objtool errors can be a manual process.  Kbuild removes the
object, so it has to be compiled or linked again before running objtool.
Then the objtool args need to be reversed engineered.

Make that all easier by automatically making a backup of the object file
on error, and print a modified version of the args which can be used to
recreate.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/builtin-check.c           | 68 +++++++++++++++++++++++--
 tools/objtool/include/objtool/builtin.h |  1 -
 tools/objtool/objtool.c                 | 63 -----------------------
 3 files changed, 65 insertions(+), 67 deletions(-)

diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index c201650efe49..39ddca64cb58 100644
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -91,7 +91,6 @@ static const struct option check_options[] = {
 
 	OPT_GROUP("Options:"),
 	OPT_BOOLEAN(0,   "backtrace", &opts.backtrace, "unwind on error"),
-	OPT_BOOLEAN(0,   "backup", &opts.backup, "create .orig files before modification"),
 	OPT_BOOLEAN(0,   "dry-run", &opts.dryrun, "don't write modifications"),
 	OPT_BOOLEAN(0,   "link", &opts.link, "object is a linked object"),
 	OPT_BOOLEAN(0,   "module", &opts.module, "object is part of a kernel module"),
@@ -228,10 +227,39 @@ static int copy_file(const char *src, const char *dst)
 	return 0;
 }
 
+static char **save_argv(int argc, const char **argv)
+{
+	char **orig_argv;
+
+	orig_argv = calloc(argc, sizeof(char *));
+	if (!orig_argv) {
+		perror("calloc");
+		return NULL;
+	}
+
+	for (int i = 0; i < argc; i++) {
+		orig_argv[i] = strdup(argv[i]);
+		if (!orig_argv[i]) {
+			perror("strdup");
+			return NULL;
+		}
+	};
+
+	return orig_argv;
+}
+
+#define ORIG_SUFFIX ".orig"
+
 int objtool_run(int argc, const char **argv)
 {
 	struct objtool_file *file;
-	int ret;
+	char *backup = NULL;
+	char **orig_argv;
+	int ret = 0;
+
+	orig_argv = save_argv(argc, argv);
+	if (!orig_argv)
+		return 1;
 
 	cmd_parse_options(argc, argv, check_usage);
 
@@ -271,8 +299,42 @@ int objtool_run(int argc, const char **argv)
 	return 0;
 
 err:
-	if (opts.output)
+	if (opts.dryrun)
+		goto err_msg;
+
+	if (opts.output) {
 		unlink(opts.output);
+		goto err_msg;
+	}
+
+	/*
+	 * Make a backup before kbuild deletes the file so the error
+	 * can be recreated without recompiling or relinking.
+	 */
+	backup = malloc(strlen(objname) + strlen(ORIG_SUFFIX) + 1);
+	if (!backup) {
+		perror("malloc");
+		return 1;
+	}
+
+	strcpy(backup, objname);
+	strcat(backup, ORIG_SUFFIX);
+	if (copy_file(objname, backup))
+		return 1;
+
+err_msg:
+	fprintf(stderr, "%s", orig_argv[0]);
+
+	for (int i = 1; i < argc; i++) {
+		char *arg = orig_argv[i];
+
+		if (backup && !strcmp(arg, objname))
+			fprintf(stderr, " %s -o %s", backup, objname);
+		else
+			fprintf(stderr, " %s", arg);
+	}
+
+	fprintf(stderr, "\n");
 
 	return 1;
 }
diff --git a/tools/objtool/include/objtool/builtin.h b/tools/objtool/include/objtool/builtin.h
index b18f114cdaa4..0fafd0f7a209 100644
--- a/tools/objtool/include/objtool/builtin.h
+++ b/tools/objtool/include/objtool/builtin.h
@@ -29,7 +29,6 @@ struct opts {
 
 	/* options: */
 	bool backtrace;
-	bool backup;
 	bool dryrun;
 	bool link;
 	bool mnop;
diff --git a/tools/objtool/objtool.c b/tools/objtool/objtool.c
index 53cd881c6b95..1c73fb62fd57 100644
--- a/tools/objtool/objtool.c
+++ b/tools/objtool/objtool.c
@@ -20,64 +20,6 @@ bool help;
 
 static struct objtool_file file;
 
-static bool objtool_create_backup(const char *_objname)
-{
-	int len = strlen(_objname);
-	char *buf, *base, *name = malloc(len+6);
-	int s, d, l, t;
-
-	if (!name) {
-		perror("failed backup name malloc");
-		return false;
-	}
-
-	strcpy(name, _objname);
-	strcpy(name + len, ".orig");
-
-	d = open(name, O_CREAT|O_WRONLY|O_TRUNC, 0644);
-	if (d < 0) {
-		perror("failed to create backup file");
-		return false;
-	}
-
-	s = open(_objname, O_RDONLY);
-	if (s < 0) {
-		perror("failed to open orig file");
-		return false;
-	}
-
-	buf = malloc(4096);
-	if (!buf) {
-		perror("failed backup data malloc");
-		return false;
-	}
-
-	while ((l = read(s, buf, 4096)) > 0) {
-		base = buf;
-		do {
-			t = write(d, base, l);
-			if (t < 0) {
-				perror("failed backup write");
-				return false;
-			}
-			base += t;
-			l -= t;
-		} while (l);
-	}
-
-	if (l < 0) {
-		perror("failed backup read");
-		return false;
-	}
-
-	free(name);
-	free(buf);
-	close(d);
-	close(s);
-
-	return true;
-}
-
 struct objtool_file *objtool_open_read(const char *filename)
 {
 	if (file.elf) {
@@ -89,11 +31,6 @@ struct objtool_file *objtool_open_read(const char *filename)
 	if (!file.elf)
 		return NULL;
 
-	if (opts.backup && !objtool_create_backup(objname)) {
-		WARN("can't create backup file");
-		return NULL;
-	}
-
 	hash_init(file.insn_hash);
 	INIT_LIST_HEAD(&file.retpoline_call_list);
 	INIT_LIST_HEAD(&file.return_thunk_list);
-- 
2.48.1
Re: [PATCH 12/13] objtool: Create backup on error and print args
Posted by Miroslav Benes 9 months ago
On Fri, 14 Mar 2025, Josh Poimboeuf wrote:

> Recreating objtool errors can be a manual process.  Kbuild removes the
> object, so it has to be compiled or linked again before running objtool.
> Then the objtool args need to be reversed engineered.
> 
> Make that all easier by automatically making a backup of the object file
> on error, and print a modified version of the args which can be used to
> recreate.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Reviewed-by: Miroslav Benes <mbenes@suse.cz>

M
Re: [PATCH 12/13] objtool: Create backup on error and print args
Posted by Brendan Jackman 9 months ago
On Fri, Mar 14, 2025 at 12:29:10PM -0700, Josh Poimboeuf wrote:
> Recreating objtool errors can be a manual process.  Kbuild removes the
> object, so it has to be compiled or linked again before running objtool.
> Then the objtool args need to be reversed engineered.
> 
> Make that all easier by automatically making a backup of the object file
> on error, and print a modified version of the args which can be used to
> recreate.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
>  		unlink(opts.output);
> +		goto err_msg;
> +	}
> +
> +	/*
> +	 * Make a backup before kbuild deletes the file so the error
> +	 * can be recreated without recompiling or relinking.
> +	 */
> +	backup = malloc(strlen(objname) + strlen(ORIG_SUFFIX) + 1);
> +	if (!backup) {
> +		perror("malloc");
> +		return 1;
> +	}
> +
> +	strcpy(backup, objname);
> +	strcat(backup, ORIG_SUFFIX);
> +	if (copy_file(objname, backup))
> +		return 1;
> +

I think there should be a comment here like

/*
 * Dump a command line with the original filename replaced with the
 * backup filename.
 */

With the context from the comment above it's obvious enough _why_
the code would do this, but it still takes a few unnecessary brain
cycles to figure out _that_ it's doing that.

Or alternatively just print "command line to reproduce:" before the
modfified argv or whatever.