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Message-ID: <20251119143247.3944213-21-alexandre.chartre@oracle.com>
Date: Wed, 19 Nov 2025 15:32:37 +0100
From: Alexandre Chartre <alexandre.chartre@...cle.com>
To: linux-kernel@...r.kernel.org, mingo@...nel.org, jpoimboe@...nel.org,
peterz@...radead.org, david.laight.linux@...il.com
Cc: alexandre.chartre@...cle.com
Subject: [PATCH v5 20/30] objtool: Disassemble group alternatives
When using the --disas option, disassemble all group alternatives.
Jump tables and exception tables (which are handled as alternatives)
are not disassembled at the moment.
Signed-off-by: Alexandre Chartre <alexandre.chartre@...cle.com>
---
tools/objtool/disas.c | 166 +++++++++++++++++++++++++++++++++++++-----
1 file changed, 149 insertions(+), 17 deletions(-)
diff --git a/tools/objtool/disas.c b/tools/objtool/disas.c
index f9b13d56acab7..ae69bef2eb37e 100644
--- a/tools/objtool/disas.c
+++ b/tools/objtool/disas.c
@@ -47,8 +47,14 @@ struct disas_alt {
struct alternative *alt; /* alternative or NULL if default code */
char *name; /* name for this alternative */
int width; /* formatting width */
+ char *insn[DISAS_ALT_INSN_MAX]; /* alternative instructions */
};
+#define DALT_DEFAULT(dalt) (!(dalt)->alt)
+#define DALT_INSN(dalt) (DALT_DEFAULT(dalt) ? (dalt)->orig_insn : (dalt)->alt->insn)
+#define DALT_GROUP(dalt) (DALT_INSN(dalt)->alt_group)
+#define DALT_ALTID(dalt) ((dalt)->orig_insn->offset)
+
/*
* Wrapper around asprintf() to allocate and format a string.
* Return the allocated string or NULL on error.
@@ -506,6 +512,21 @@ size_t disas_insn(struct disas_context *dctx, struct instruction *insn)
return disasm(insn->offset, &dctx->info);
}
+static struct instruction *next_insn_same_alt(struct objtool_file *file,
+ struct alt_group *alt_grp,
+ struct instruction *insn)
+{
+ if (alt_grp->last_insn == insn || alt_grp->nop == insn)
+ return NULL;
+
+ return next_insn_same_sec(file, insn);
+}
+
+#define alt_for_each_insn(file, alt_grp, insn) \
+ for (insn = alt_grp->first_insn; \
+ insn; \
+ insn = next_insn_same_alt(file, alt_grp, insn))
+
/*
* Provide a name for the type of alternatives present at the
* specified instruction.
@@ -594,23 +615,107 @@ static int disas_alt_init(struct disas_alt *dalt,
return 0;
}
+static int disas_alt_add_insn(struct disas_alt *dalt, int index, char *insn_str)
+{
+ int len;
+
+ if (index >= DISAS_ALT_INSN_MAX) {
+ WARN("Alternative %lx.%s has more instructions than supported",
+ DALT_ALTID(dalt), dalt->name);
+ return -1;
+ }
+
+ len = strlen(insn_str);
+ dalt->insn[index] = insn_str;
+ if (len > dalt->width)
+ dalt->width = len;
+
+ return 0;
+}
+
+/*
+ * Disassemble an alternative and store instructions in the disas_alt
+ * structure. Return the number of instructions in the alternative.
+ */
+static int disas_alt_group(struct disas_context *dctx, struct disas_alt *dalt)
+{
+ struct objtool_file *file;
+ struct instruction *insn;
+ char *str;
+ int count;
+ int err;
+
+ file = dctx->file;
+ count = 0;
+
+ alt_for_each_insn(file, DALT_GROUP(dalt), insn) {
+
+ disas_insn(dctx, insn);
+ str = strdup(disas_result(dctx));
+ if (!str)
+ return -1;
+
+ err = disas_alt_add_insn(dalt, count, str);
+ if (err)
+ break;
+ count++;
+ }
+
+ return count;
+}
+
+/*
+ * Disassemble the default alternative.
+ */
+static int disas_alt_default(struct disas_context *dctx, struct disas_alt *dalt)
+{
+ char *str;
+ int err;
+
+ if (DALT_GROUP(dalt))
+ return disas_alt_group(dctx, dalt);
+
+ /*
+ * Default alternative with no alt_group: this is the default
+ * code associated with either a jump table or an exception
+ * table and no other instruction alternatives. In that case
+ * the default alternative is made of a single instruction.
+ */
+ disas_insn(dctx, dalt->orig_insn);
+ str = strdup(disas_result(dctx));
+ if (!str)
+ return -1;
+ err = disas_alt_add_insn(dalt, 0, str);
+ if (err)
+ return -1;
+
+ return 1;
+}
+
/*
* Print all alternatives one above the other.
*/
static void disas_alt_print_compact(char *alt_name, struct disas_alt *dalts,
- int alt_count)
+ int alt_count, int insn_count)
{
struct instruction *orig_insn;
+ int i, j;
int len;
- int i;
orig_insn = dalts[0].orig_insn;
len = disas_print(stdout, orig_insn->sec, orig_insn->offset, 0, NULL);
printf("%s\n", alt_name);
- for (i = 0; i < alt_count; i++)
+ for (i = 0; i < alt_count; i++) {
printf("%*s= %s\n", len, "", dalts[i].name);
+ for (j = 0; j < insn_count; j++) {
+ if (!dalts[i].insn[j])
+ break;
+ printf("%*s| %s\n", len, "", dalts[i].insn[j]);
+ }
+ printf("%*s|\n", len, "");
+ }
}
/*
@@ -624,11 +729,15 @@ static void *disas_alt(struct disas_context *dctx,
struct instruction *orig_insn)
{
struct disas_alt dalts[DISAS_ALT_MAX] = { 0 };
+ struct instruction *last_insn = NULL;
struct alternative *alt;
+ struct disas_alt *dalt;
+ int insn_count = 0;
int alt_count = 0;
char *alt_name;
+ int count;
+ int i, j;
int err;
- int i;
alt_name = strfmt("<%s.%lx>", disas_alt_type_name(orig_insn),
orig_insn->offset);
@@ -639,7 +748,7 @@ static void *disas_alt(struct disas_context *dctx,
}
/*
- * Initialize the default alternative.
+ * Initialize and disassemble the default alternative.
*/
err = disas_alt_init(&dalts[0], orig_insn, NULL);
if (err) {
@@ -647,8 +756,14 @@ static void *disas_alt(struct disas_context *dctx,
goto done;
}
+ insn_count = disas_alt_default(dctx, &dalts[0]);
+ if (insn_count < 0) {
+ WARN("%s: failed to disassemble default alternative", alt_name);
+ goto done;
+ }
+
/*
- * Initialize all other alternatives.
+ * Initialize and disassemble all other alternatives.
*/
i = 1;
for (alt = orig_insn->alts; alt; alt = alt->next) {
@@ -656,35 +771,52 @@ static void *disas_alt(struct disas_context *dctx,
WARN("%s has more alternatives than supported", alt_name);
break;
}
- err = disas_alt_init(&dalts[i], orig_insn, alt);
+ dalt = &dalts[i];
+ err = disas_alt_init(dalt, orig_insn, alt);
if (err) {
WARN("%s: failed to disassemble alternative", alt_name);
goto done;
}
+ /*
+ * Only group alternatives are supported at the moment.
+ */
+ switch (dalt->alt->type) {
+ case ALT_TYPE_INSTRUCTIONS:
+ count = disas_alt_group(dctx, dalt);
+ break;
+ default:
+ count = 0;
+ }
+ if (count < 0) {
+ WARN("%s: failed to disassemble alternative %s",
+ alt_name, dalt->name);
+ goto done;
+ }
+
+ insn_count = count > insn_count ? count : insn_count;
i++;
}
alt_count = i;
/*
* Print default and non-default alternatives.
- *
- * At the moment, this just prints an header for each alternative.
*/
- disas_alt_print_compact(alt_name, dalts, alt_count);
+ disas_alt_print_compact(alt_name, dalts, alt_count, insn_count);
+
+ last_insn = orig_insn->alt_group ? orig_insn->alt_group->last_insn :
+ orig_insn;
done:
- for (i = 0; i < alt_count; i++)
+ for (i = 0; i < alt_count; i++) {
free(dalts[i].name);
+ for (j = 0; j < insn_count; j++)
+ free(dalts[i].insn[j]);
+ }
free(alt_name);
- /*
- * Currently we are not disassembling any alternative but just
- * printing alternative names. Return NULL to have disas_func()
- * resume the disassembly with the default alternative.
- */
- return NULL;
+ return last_insn;
}
/*
--
2.43.5
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