[PATCH v6 19/26] perf trace: Add an option to disable syscall augmentation

[Ian Rogers <irogers@google.com>]

perf trace falls back to the raw_syscalls tracepoints, filtering in user
space, when the augmentation BPF programs can't be loaded. Add
--no-syscall-augment to use that path even when they can, so both can
be tested. Suggest it when tasks are lost, as the tracepoints' per-task
events don't limit how many tasks are traced.

Assisted-by: Antigravity:gemini-3.1-pro
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/Documentation/perf-trace.txt |  6 ++++++
 tools/perf/builtin-trace.c              | 10 +++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/tools/perf/Documentation/perf-trace.txt b/tools/perf/Documentation/perf-trace.txt
index d20b43ea3d37..fabb37258751 100644
--- a/tools/perf/Documentation/perf-trace.txt
+++ b/tools/perf/Documentation/perf-trace.txt
@@ -172,6 +172,12 @@ the thread executes on the designated CPUs. Default is to monitor all CPUs.
 	Trace system calls. This options is enabled by default, disable with
 	--no-syscalls.
 
+--syscall-augment::
+	Augment system call arguments using BPF, the default when BPF support
+	is available. Disable with --no-syscall-augment to use the
+	raw_syscalls tracepoints instead, such as when more tasks are alive
+	at once than augmentation can trace.
+
 --call-graph [mode,type,min[,limit],order[,key][,branch]]::
         Setup and enable call-graph (stack chain/backtrace) recording.
         See `--call-graph` section in perf-record and perf-report
diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index 1be355a3ae22..c34c9f129836 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -216,6 +216,7 @@ struct trace {
 	bool			print_sample;
 	bool			show_tool_stats;
 	bool			trace_syscalls;
+	bool			syscall_augment;
 	bool			libtraceevent_print;
 	bool			kernel_syscallchains;
 	s16			args_alignment;
@@ -5002,7 +5003,8 @@ static int trace__run(struct trace *trace, int argc, const char **argv)
 	lost_tasks = augmented_syscalls__lost_tasks();
 	if (lost_tasks)
 		color_fprintf(trace->output, PERF_COLOR_RED,
-			      "LOST the syscalls of %d tasks, too many to trace at once!\n",
+			      "LOST the syscalls of %d tasks, too many to trace at once!\n"
+			      "Use --no-syscall-augment to trace them without augmentation.\n",
 			      lost_tasks);
 
 	if (!err) {
@@ -5788,6 +5790,7 @@ int cmd_trace(int argc, const char **argv)
 		.show_arg_names = true,
 		.args_alignment = 70,
 		.trace_syscalls = false,
+		.syscall_augment = true,
 		.kernel_syscallchains = false,
 		.max_stack = UINT_MAX,
 		.max_events = ULONG_MAX,
@@ -5843,6 +5846,8 @@ int cmd_trace(int argc, const char **argv)
 	OPT_CALLBACK_DEFAULT('F', "pf", &trace.trace_pgfaults, "all|maj|min",
 		     "Trace pagefaults", parse_pagefaults, "maj"),
 	OPT_BOOLEAN(0, "syscalls", &trace.trace_syscalls, "Trace syscalls"),
+	OPT_BOOLEAN(0, "syscall-augment", &trace.syscall_augment,
+		    "Augment syscalls using BPF"),
 	OPT_BOOLEAN('f', "force", &trace.force, "don't complain, do it"),
 	OPT_CALLBACK(0, "call-graph", &trace.opts,
 		     "record_mode[,record_size]", record_callchain_help,
@@ -5982,6 +5987,9 @@ int cmd_trace(int argc, const char **argv)
 			goto skip_augmentation;
 	}
 
+	if (!trace.syscall_augment)
+		goto skip_augmentation;
+
 	err = augmented_syscalls__prepare();
 	if (err < 0)
 		goto skip_augmentation;
-- 
2.56.0.rc1.315.gc6ed9934b7-goog