perf trace: Make syscall table stable

Namhyung fixed the syscall table being reallocated and moving by
reloading the system call pointer after a move:
https://lore.kernel.org/lkml/Z9YHCzINiu4uBQ8B@google.com/
This could be brittle so this patch changes the syscall table to be an
array of pointers of "struct syscall" that don't move. Remove
unnecessary copies and searches with this change.

Signed-off-by: Ian Rogers <irogers@google.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Arnaldo Carvalho de Melo <acme@kernel.org>
Link: https://lore.kernel.org/r/20250319050741.269828-13-irogers@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

Author: captain5050

tools/perf/builtin-trace.c

@@ -151,7 +151,7 @@ struct trace {
 	struct perf_tool	tool;
 	struct {
 		/** Sorted sycall numbers used by the trace. */
-		struct syscall  *table;
+		struct syscall  **table;
 		/** Size of table. */
 		size_t		table_size;
 		struct {
@@ -2473,24 +2473,41 @@ static size_t syscall__scnprintf_args(struct syscall *sc, char *bf, size_t size,
 	return printed;
 }
 
-static void syscall__init(struct syscall *sc, int e_machine, int id)
+static struct syscall *syscall__new(int e_machine, int id)
 {
-	memset(sc, 0, sizeof(*sc));
+	struct syscall *sc = zalloc(sizeof(*sc));
+
+	if (!sc)
+		return NULL;
+
 	sc->e_machine = e_machine;
 	sc->id = id;
+	return sc;
 }
 
-static void syscall__exit(struct syscall *sc)
+static void syscall__delete(struct syscall *sc)
 {
 	if (!sc)
 		return;
 
-	zfree(&sc->arg_fmt);
+	free(sc->arg_fmt);
+	free(sc);
+}
+
+static int syscall__bsearch_cmp(const void *key, const void *entry)
+{
+	const struct syscall *a = key, *b = *((const struct syscall **)entry);
+
+	if (a->e_machine != b->e_machine)
+		return a->e_machine - b->e_machine;
+
+	return a->id - b->id;
 }
 
 static int syscall__cmp(const void *va, const void *vb)
 {
-	const struct syscall *a = va, *b = vb;
+	const struct syscall *a = *((const struct syscall **)va);
+	const struct syscall *b = *((const struct syscall **)vb);
 
 	if (a->e_machine != b->e_machine)
 		return a->e_machine - b->e_machine;
@@ -2504,27 +2521,33 @@ static struct syscall *trace__find_syscall(struct trace *trace, int e_machine, i
 		.e_machine = e_machine,
 		.id = id,
 	};
-	struct syscall *sc, *tmp;
+	struct syscall *sc, **tmp;
 
 	if (trace->syscalls.table) {
-		sc = bsearch(&key, trace->syscalls.table, trace->syscalls.table_size,
-			     sizeof(struct syscall), syscall__cmp);
-		if (sc)
-			return sc;
+		struct syscall **sc_entry = bsearch(&key, trace->syscalls.table,
+						    trace->syscalls.table_size,
+						    sizeof(trace->syscalls.table[0]),
+						    syscall__bsearch_cmp);
+
+		if (sc_entry)
+			return *sc_entry;
 	}
 
+	sc = syscall__new(e_machine, id);
+	if (!sc)
+		return NULL;
+
 	tmp = reallocarray(trace->syscalls.table, trace->syscalls.table_size + 1,
-			   sizeof(struct syscall));
-	if (!tmp)
+			   sizeof(trace->syscalls.table[0]));
+	if (!tmp) {
+		syscall__delete(sc);
 		return NULL;
+	}
 
 	trace->syscalls.table = tmp;
-	sc = &trace->syscalls.table[trace->syscalls.table_size++];
-	syscall__init(sc, e_machine, id);
-	qsort(trace->syscalls.table, trace->syscalls.table_size, sizeof(struct syscall),
+	trace->syscalls.table[trace->syscalls.table_size++] = sc;
+	qsort(trace->syscalls.table, trace->syscalls.table_size, sizeof(trace->syscalls.table[0]),
 	      syscall__cmp);
-	sc = bsearch(&key, trace->syscalls.table, trace->syscalls.table_size,
-		     sizeof(struct syscall), syscall__cmp);
 	return sc;
 }
 
@@ -3855,33 +3878,32 @@ static int trace__bpf_sys_enter_beauty_map(struct trace *trace, int e_machine, i
 	return -1;
 }
 
-static struct bpf_program *trace__find_usable_bpf_prog_entry(struct trace *trace, struct syscall *_sc)
+static struct bpf_program *trace__find_usable_bpf_prog_entry(struct trace *trace,
+							     struct syscall *sc)
 {
-	struct syscall sc = *_sc; /* Copy as trace__syscall_info may invalidate pointer. */
 	struct tep_format_field *field, *candidate_field;
 	/*
 	 * We're only interested in syscalls that have a pointer:
 	 */
-	for (field = sc.args; field; field = field->next) {
+	for (field = sc->args; field; field = field->next) {
 		if (field->flags & TEP_FIELD_IS_POINTER)
 			goto try_to_find_pair;
 	}
 
 	return NULL;
 
 try_to_find_pair:
-	for (int i = 0, num_idx = syscalltbl__num_idx(sc.e_machine); i < num_idx; ++i) {
-		int id = syscalltbl__id_at_idx(sc.e_machine, i);
-		/* calling trace__syscall_info() may invalidate '_sc' */
-		struct syscall *pair = trace__syscall_info(trace, NULL, sc.e_machine, id);
+	for (int i = 0, num_idx = syscalltbl__num_idx(sc->e_machine); i < num_idx; ++i) {
+		int id = syscalltbl__id_at_idx(sc->e_machine, i);
+		struct syscall *pair = trace__syscall_info(trace, NULL, sc->e_machine, id);
 		struct bpf_program *pair_prog;
 		bool is_candidate = false;
 
-		if (pair == NULL || pair->id == sc.id ||
+		if (pair == NULL || pair->id == sc->id ||
 		    pair->bpf_prog.sys_enter == trace->skel->progs.syscall_unaugmented)
 			continue;
 
-		for (field = sc.args, candidate_field = pair->args;
+		for (field = sc->args, candidate_field = pair->args;
 		     field && candidate_field; field = field->next, candidate_field = candidate_field->next) {
 			bool is_pointer = field->flags & TEP_FIELD_IS_POINTER,
 			     candidate_is_pointer = candidate_field->flags & TEP_FIELD_IS_POINTER;
@@ -3948,7 +3970,8 @@ static struct bpf_program *trace__find_usable_bpf_prog_entry(struct trace *trace
 				goto next_candidate;
 		}
 
-		pr_debug("Reusing \"%s\" BPF sys_enter augmenter for \"%s\"\n", pair->name, sc.name);
+		pr_debug("Reusing \"%s\" BPF sys_enter augmenter for \"%s\"\n", pair->name,
+			 sc->name);
 		return pair_prog;
 	next_candidate:
 		continue;
@@ -4044,11 +4067,7 @@ static int trace__init_syscalls_bpf_prog_array_maps(struct trace *trace, int e_m
 		pair_prog = trace__find_usable_bpf_prog_entry(trace, sc);
 		if (pair_prog == NULL)
 			continue;
-		/*
-		 * Get syscall info again as find usable entry above might
-		 * modify the syscall table and shuffle it.
-		 */
-		sc = trace__syscall_info(trace, NULL, e_machine, key);
+
 		sc->bpf_prog.sys_enter = pair_prog;
 
 		/*
@@ -5316,7 +5335,7 @@ static void trace__exit(struct trace *trace)
 	zfree(&trace->ev_qualifier_ids.entries);
 	if (trace->syscalls.table) {
 		for (size_t i = 0; i < trace->syscalls.table_size; i++)
-			syscall__exit(&trace->syscalls.table[i]);
+			syscall__delete(trace->syscalls.table[i]);
 		zfree(&trace->syscalls.table);
 	}
 	zfree(&trace->perfconfig_events);