perf trace: Add --force-btf for debugging

If --force-btf is enabled, prefer btf_dump general pretty printer to
perf trace's customized pretty printers.

Mostly for debug purposes.

Committer testing:

diff before/after shows we need several improvements to be able to
compare the changes, first we need to cut off/disable mutable data such
as pids and timestamps, then what is left are the buffer addresses
passed from userspace, returned from kernel space, maybe we can ask
'perf trace' to go on making those reproducible.

That would entail a Pointer Address Translation (PAT) like for
networking, that would, for simple, reproducible if not for these
details, workloads, that we would then use in our regression tests.

Enough digression, this is one such diff:

   openat(dfd: CWD, filename: "/usr/share/locale/locale.alias", flags: RDONLY|CLOEXEC) = 3
  -fstat(fd: 3, statbuf: 0x7fff01f212a0)                                 = 0
  -read(fd: 3, buf: 0x5596bab2d630, count: 4096)                         = 2998
  -read(fd: 3, buf: 0x5596bab2d630, count: 4096)                         = 0
  +fstat(fd: 3, statbuf: 0x7ffc163cf0e0)                                 = 0
  +read(fd: 3, buf: 0x55b4e0631630, count: 4096)                         = 2998
  +read(fd: 3, buf: 0x55b4e0631630, count: 4096)                         = 0
   close(fd: 3)                                                          = 0
   openat(dfd: CWD, filename: "/usr/share/locale/en_US.UTF-8/LC_MESSAGES/coreutils.mo") = -1 ENOENT (No such file or directory)
   openat(dfd: CWD, filename: "/usr/share/locale/en_US.utf8/LC_MESSAGES/coreutils.mo") = -1 ENOENT (No such file or directory)
  @@ -45,7 +45,7 @@
   openat(dfd: CWD, filename: "/usr/share/locale/en.UTF-8/LC_MESSAGES/coreutils.mo") = -1 ENOENT (No such file or directory)
   openat(dfd: CWD, filename: "/usr/share/locale/en.utf8/LC_MESSAGES/coreutils.mo") = -1 ENOENT (No such file or directory)
   openat(dfd: CWD, filename: "/usr/share/locale/en/LC_MESSAGES/coreutils.mo") = -1 ENOENT (No such file or directory)
  -{ .tv_sec: 1, .tv_nsec: 0 }, rmtp: 0x7fff01f21990) = 0
  +(struct __kernel_timespec){.tv_sec = (__kernel_time64_t)1,}, rmtp: 0x7ffc163cf7d0) =

The problem more close to our hands is to make the libbpf BTF pretty
printer to have a mode that closely resembles what we're trying to
resemble: strace output.

Being able to run something with 'perf trace' and with 'strace' and get
the exact same output should be of interest of anybody wanting to have
strace and 'perf trace' regression tested against each other.

That last part is 'perf trace' shot at being something so useful as
strace... ;-)

Suggested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Howard Chu <howardchu95@gmail.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20240824163322.60796-8-howardchu95@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index dab6d905015dd15553a268d3623d06fce61e8530..c47fde936c33a2e605b4aa5a36dacd96904c7716 100644 (file)
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -212,6 +212,7 @@ struct trace {
        bool                    show_string_prefix;
        bool                    force;
        bool                    vfs_getname;
+       bool                    force_btf;
        int                     trace_pgfaults;
        char                    *perfconfig_events;
        struct {
@@ -2363,7 +2364,9 @@ static size_t syscall__scnprintf_args(struct syscall *sc, char *bf, size_t size,
 
                        default_scnprintf = sc->arg_fmt[arg.idx].scnprintf;
 
-                       if (default_scnprintf == NULL || default_scnprintf == SCA_PTR) {
+                       if (trace->force_btf ||
+                           (default_scnprintf == NULL ||
+                            (default_scnprintf == SCA_PTR && strstr(field->type, "struct")))) {
                                btf_printed = trace__btf_scnprintf(trace, &arg, bf + printed,
                                                                   size - printed, val, field->type);
                                if (btf_printed) {
@@ -5171,6 +5174,8 @@ int cmd_trace(int argc, const char **argv)
        OPT_INTEGER('D', "delay", &trace.opts.target.initial_delay,
                     "ms to wait before starting measurement after program "
                     "start"),
+       OPT_BOOLEAN(0, "force-btf", &trace.force_btf, "Prefer btf_dump general pretty printer"
+                      "to customized ones"),
        OPTS_EVSWITCH(&trace.evswitch),
        OPT_END()
        };