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Message-ID: <20251113164917.2563486-18-alexandre.chartre@oracle.com>
Date: Thu, 13 Nov 2025 17:49:06 +0100
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: [PATCH v4 17/28] objtool: Print headers for alternatives
When using the --disas option, objtool doesn't currently disassemble
any alternative. Print an header for each alternative. This identifies
places where alternatives are present but alternative code is still
not disassembled at the moment.
Signed-off-by: Alexandre Chartre <alexandre.chartre@...cle.com>
---
tools/objtool/disas.c | 154 ++++++++++++++++++++++++++++++++++++++++--
1 file changed, 148 insertions(+), 6 deletions(-)
diff --git a/tools/objtool/disas.c b/tools/objtool/disas.c
index 9b5d9075ab2d3..57a13da5e1b39 100644
--- a/tools/objtool/disas.c
+++ b/tools/objtool/disas.c
@@ -29,6 +29,43 @@ struct disas_context {
struct disassemble_info info;
};
+/*
+ * Maximum number of alternatives
+ */
+#define DISAS_ALT_MAX 5
+
+/*
+ * Maximum number of instructions per alternative
+ */
+#define DISAS_ALT_INSN_MAX 50
+
+/*
+ * Information to disassemble an alternative
+ */
+struct disas_alt {
+ struct instruction *orig_insn; /* original instruction */
+ struct alternative *alt; /* alternative or NULL if default code */
+ char *name; /* name for this alternative */
+ int width; /* formatting width */
+};
+
+/*
+ * Wrapper around asprintf() to allocate and format a string.
+ * Return the allocated string or NULL on error.
+ */
+static char *strfmt(const char *fmt, ...)
+{
+ va_list ap;
+ char *str;
+ int rv;
+
+ va_start(ap, fmt);
+ rv = vasprintf(&str, fmt, ap);
+ va_end(ap);
+
+ return rv == -1 ? NULL : str;
+}
+
static int sprint_name(char *str, const char *name, unsigned long offset)
{
int len;
@@ -317,6 +354,9 @@ char *disas_result(struct disas_context *dctx)
#define DISAS_INSN_OFFSET_SPACE 10
#define DISAS_INSN_SPACE 60
+#define DISAS_PRINSN(dctx, insn, depth) \
+ disas_print_insn(stdout, dctx, insn, depth, "\n")
+
/*
* Print a message in the instruction flow. If insn is not NULL then
* the instruction address is printed in addition of the message,
@@ -462,21 +502,123 @@ char *disas_alt_name(struct alternative *alt)
return str;
}
+/*
+ * Initialize an alternative. The default alternative should be initialized
+ * with alt=NULL.
+ */
+static int disas_alt_init(struct disas_alt *dalt,
+ struct instruction *orig_insn,
+ struct alternative *alt,
+ int alt_num)
+{
+ dalt->orig_insn = orig_insn;
+ dalt->alt = alt;
+ dalt->name = alt ? strfmt("ALTERNATIVE %d", alt_num) :
+ strfmt("<alternative.%lx>", orig_insn->offset);
+ if (!dalt->name)
+ return -1;
+ dalt->width = strlen(dalt->name);
+
+ return 0;
+}
+
+/*
+ * Disassemble an alternative.
+ *
+ * Return the last instruction in the default alternative so that
+ * disassembly can continue with the next instruction. Return NULL
+ * on error.
+ */
+static void *disas_alt(struct disas_context *dctx,
+ struct instruction *orig_insn)
+{
+ struct disas_alt alts[DISAS_ALT_MAX] = { 0 };
+ struct alternative *alt;
+ int alt_count;
+ int alt_id;
+ int i;
+ int err;
+
+ alt_id = orig_insn->offset;
+
+ /*
+ * Initialize the default alternative.
+ */
+ err = disas_alt_init(&alts[0], orig_insn, NULL, 0);
+ if (err)
+ goto error;
+
+ /*
+ * Initialize all other alternatives.
+ */
+ i = 1;
+ for (alt = orig_insn->alts; alt; alt = alt->next) {
+ if (i >= DISAS_ALT_MAX) {
+ WARN("Alternative %lx has more alternatives than supported",
+ orig_insn->offset);
+ break;
+ }
+ err = disas_alt_init(&alts[i], orig_insn, alt, i);
+ if (err)
+ goto error;
+
+ i++;
+ }
+ alt_count = i;
+
+ /*
+ * Print an header with the name of each alternative.
+ */
+ disas_print_info(stdout, orig_insn, -2, NULL);
+ for (i = 0; i < alt_count; i++) {
+ printf("| %-*s ", alts[i].width, alts[i].name);
+ free(alts[i].name);
+ }
+ printf("\n");
+
+ /*
+ * 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;
+
+error:
+ WARN("Failed to disassemble alternative %x", alt_id);
+
+ for (i = 0; i < DISAS_ALT_MAX; i++)
+ free(alts[i].name);
+
+ return NULL;
+}
+
/*
* Disassemble a function.
*/
static void disas_func(struct disas_context *dctx, struct symbol *func)
{
+ struct instruction *insn_start;
struct instruction *insn;
- size_t addr;
printf("%s:\n", func->name);
sym_for_each_insn(dctx->file, func, insn) {
- addr = insn->offset;
- disas_insn(dctx, insn);
- printf(" %6lx: %s+0x%-6lx %s\n",
- addr, func->name, addr - func->offset,
- disas_result(dctx));
+ if (insn->alts) {
+ insn_start = insn;
+ insn = disas_alt(dctx, insn);
+ if (insn)
+ continue;
+ /*
+ * There was an error with disassembling
+ * the alternative. Resume disassembling
+ * at the current instruction, this will
+ * disassemble the default alternative
+ * only and continue with the code after
+ * the alternative.
+ */
+ insn = insn_start;
+ }
+
+ DISAS_PRINSN(dctx, insn, 0);
}
printf("\n");
}
--
2.43.5
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