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Message-ID: <20251112160315.2207947-15-alexandre.chartre@oracle.com>
Date: Wed, 12 Nov 2025 17:03:01 +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 v3 14/28] objtool: Improve tracing of alternative instructions
When tracing function validation, improve the reporting of
alternative instruction by more clearly showing the different
alternatives beginning and end.
Signed-off-by: Alexandre Chartre <alexandre.chartre@...cle.com>
---
tools/objtool/check.c | 32 +++++++++++++---
tools/objtool/include/objtool/trace.h | 43 +++++++++++++++++++++
tools/objtool/trace.c | 55 +++++++++++++++++++++++++++
3 files changed, 124 insertions(+), 6 deletions(-)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 93268b7c015e3..de3ddb0fd6198 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3527,7 +3527,7 @@ static bool skip_alt_group(struct instruction *insn)
/* ANNOTATE_IGNORE_ALTERNATIVE */
if (insn->alt_group->ignore) {
- TRACE_INSN(insn, "alt group ignored");
+ TRACE_ALT(insn, "alt group ignored");
return true;
}
@@ -3649,24 +3649,44 @@ static int validate_insn(struct objtool_file *file, struct symbol *func,
return 1;
if (insn->alts) {
+ char alt_name[35];
int i, num_alts;
num_alts = 0;
- for (alt = insn->alts; alt; alt = alt->next)
- num_alts++;
+ for (alt = insn->alts; alt; alt = alt->next) {
+ if (alt->type == ALT_TYPE_INSTRUCTIONS)
+ num_alts++;
+ }
i = 1;
for (alt = insn->alts; alt; alt = alt->next) {
- TRACE_INSN(insn, "alternative %d/%d", i, num_alts);
+ if (trace) {
+ switch (alt->type) {
+ case ALT_TYPE_EX_TABLE:
+ strcpy(alt_name, "EXCEPTION");
+ break;
+ case ALT_TYPE_JUMP_TABLE:
+ strcpy(alt_name, "JUMP");
+ break;
+ case ALT_TYPE_INSTRUCTIONS:
+ snprintf(alt_name, sizeof(alt_name),
+ "ALTERNATIVE %d/%d", i, num_alts);
+ break;
+ }
+ trace_alt_begin(insn, alt, alt_name);
+ }
ret = validate_branch(file, func, alt->insn, *statep);
+ if (trace)
+ trace_alt_end(insn, alt, alt_name);
if (ret) {
BT_INSN(insn, "(alt)");
return ret;
}
- i++;
+ if (alt->insn->alt_group)
+ i++;
}
- TRACE_INSN(insn, "alternative orig");
+ TRACE_ALT_INFO_NOADDR(insn, "/ ", "DEFAULT");
}
if (skip_alt_group(insn))
diff --git a/tools/objtool/include/objtool/trace.h b/tools/objtool/include/objtool/trace.h
index 5b8abdb9b09fb..3282f3bc3a275 100644
--- a/tools/objtool/include/objtool/trace.h
+++ b/tools/objtool/include/objtool/trace.h
@@ -19,6 +19,21 @@ extern int trace_depth;
fprintf(stderr, fmt, ##__VA_ARGS__); \
})
+/*
+ * Print the instruction address and a message. The instruction
+ * itself is not printed.
+ */
+#define TRACE_ADDR(insn, fmt, ...) \
+({ \
+ if (trace) { \
+ disas_print_info(stderr, insn, trace_depth - 1, \
+ fmt "\n", ##__VA_ARGS__); \
+ } \
+})
+
+/*
+ * Print the instruction address, the instruction and a message.
+ */
#define TRACE_INSN(insn, fmt, ...) \
({ \
if (trace) { \
@@ -36,6 +51,20 @@ extern int trace_depth;
trace_insn_state(insn, sprev, snext); \
})
+#define TRACE_ALT_FMT(pfx, fmt) pfx "<alternative.%lx> " fmt
+
+#define TRACE_ALT(insn, fmt, ...) \
+ TRACE_INSN(insn, TRACE_ALT_FMT("", fmt), \
+ (insn)->offset, ##__VA_ARGS__)
+
+#define TRACE_ALT_INFO(insn, pfx, fmt, ...) \
+ TRACE_ADDR(insn, TRACE_ALT_FMT(pfx, fmt), \
+ (insn)->offset, ##__VA_ARGS__)
+
+#define TRACE_ALT_INFO_NOADDR(insn, pfx, fmt, ...) \
+ TRACE_ADDR(NULL, TRACE_ALT_FMT(pfx, fmt), \
+ (insn)->offset, ##__VA_ARGS__)
+
static inline void trace_enable(void)
{
trace = true;
@@ -61,17 +90,31 @@ static inline void trace_depth_dec(void)
void trace_insn_state(struct instruction *insn, struct insn_state *sprev,
struct insn_state *snext);
+void trace_alt_begin(struct instruction *orig_insn, struct alternative *alt,
+ char *alt_name);
+void trace_alt_end(struct instruction *orig_insn, struct alternative *alt,
+ char *alt_name);
#else /* DISAS */
#define TRACE(fmt, ...)
+#define TRACE_ADDR(insn, fmt, ...)
#define TRACE_INSN(insn, fmt, ...)
#define TRACE_INSN_STATE(insn, sprev, snext)
+#define TRACE_ALT(insn, fmt, ...)
+#define TRACE_ALT_INFO(insn, fmt, ...)
+#define TRACE_ALT_INFO_NOADDR(insn, fmt, ...)
static inline void trace_enable(void) {}
static inline void trace_disable(void) {}
static inline void trace_depth_inc(void) {}
static inline void trace_depth_dec(void) {}
+static inline void trace_alt_begin(struct instruction *orig_insn,
+ struct alternative *alt,
+ char *alt_name) {};
+static inline void trace_alt_end(struct instruction *orig_insn,
+ struct alternative *alt,
+ char *alt_name) {};
#endif
diff --git a/tools/objtool/trace.c b/tools/objtool/trace.c
index ef9250d4646bb..1c3d961b5123a 100644
--- a/tools/objtool/trace.c
+++ b/tools/objtool/trace.c
@@ -147,3 +147,58 @@ void trace_insn_state(struct instruction *insn, struct insn_state *sprev,
insn->trace = 1;
}
+
+void trace_alt_begin(struct instruction *orig_insn, struct alternative *alt,
+ char *alt_name)
+{
+ struct instruction *alt_insn;
+ char suffix[2];
+
+ alt_insn = alt->insn;
+
+ if (alt->type == ALT_TYPE_EX_TABLE) {
+ /*
+ * When there is an exception table then the instruction
+ * at the original location is executed but it can cause
+ * an exception. In that case, the execution will be
+ * redirected to the alternative instruction.
+ *
+ * The instruction at the original location can have
+ * instruction alternatives, so we just print the location
+ * of the instruction that can cause the exception and
+ * not the instruction itself.
+ */
+ TRACE_ALT_INFO_NOADDR(orig_insn, "/ ", "%s for instruction at 0x%lx <%s+0x%lx>",
+ alt_name,
+ orig_insn->offset, orig_insn->sym->name,
+ orig_insn->offset - orig_insn->sym->offset);
+ } else {
+ TRACE_ALT_INFO_NOADDR(orig_insn, "/ ", "%s", alt_name);
+ }
+
+ if (alt->type == ALT_TYPE_JUMP_TABLE) {
+ /*
+ * For a jump alternative, if the default instruction is
+ * a NOP then it is replaced with the jmp instruction,
+ * otherwise it is replaced with a NOP instruction.
+ */
+ trace_depth++;
+ if (orig_insn->type == INSN_NOP) {
+ suffix[0] = (orig_insn->len == 5) ? 'q' : '\0';
+ TRACE_ADDR(orig_insn, "jmp%-3s %lx <%s+0x%lx>", suffix,
+ alt_insn->offset, alt_insn->sym->name,
+ alt_insn->offset - alt_insn->sym->offset);
+ } else {
+ TRACE_ADDR(orig_insn, "NOP%d", orig_insn->len);
+ trace_depth--;
+ }
+ }
+}
+
+void trace_alt_end(struct instruction *orig_insn, struct alternative *alt,
+ char *alt_name)
+{
+ if (alt->type == ALT_TYPE_JUMP_TABLE && orig_insn->type == INSN_NOP)
+ trace_depth--;
+ TRACE_ALT_INFO_NOADDR(orig_insn, "\\ ", "%s end", alt_name);
+}
--
2.43.5
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