linux-kernel - Re: [PATCH v5 00/11] perf: Support multiple system call tables in the build

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Message-ID: <Z9SWDGsdgagMr8PV@x1>
Date: Fri, 14 Mar 2025 17:48:12 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Ian Rogers <irogers@...gle.com>, Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Kan Liang <kan.liang@...ux.intel.com>,
	John Garry <john.g.garry@...cle.com>, Will Deacon <will@...nel.org>,
	James Clark <james.clark@...aro.org>,
	Mike Leach <mike.leach@...aro.org>, Leo Yan <leo.yan@...ux.dev>,
	guoren <guoren@...nel.org>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Charlie Jenkins <charlie@...osinc.com>,
	Bibo Mao <maobibo@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Jiri Slaby <jirislaby@...nel.org>,
	Björn Töpel <bjorn@...osinc.com>,
	Howard Chu <howardchu95@...il.com>, linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	"linux-csky@...r.kernel.org" <linux-csky@...r.kernel.org>,
	linux-riscv@...ts.infradead.org, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v5 00/11] perf: Support multiple system call tables in
 the build

On Fri, Mar 14, 2025 at 02:26:41PM -0300, Arnaldo Carvalho de Melo wrote:
> it finds the pair, but then its sc->args has a bogus pointer... I'll see
> where this isn't being initialized...

Breakpoint 4, trace__find_usable_bpf_prog_entry (trace=0x7fffffffa510, sc=0x1046f10) at builtin-trace.c:3874
3874			bool is_candidate = false;
(gdb) n
3876			if (pair == NULL || pair == sc ||
(gdb) p pair
$7 = (struct syscall *) 0x1083c50
(gdb) p pair->name
$8 = 0x81478e "accept4"
(gdb) n
3877			    pair->bpf_prog.sys_enter == trace->skel->progs.syscall_unaugmented)
(gdb) p i
$9 = 1
(gdb) n
3876			if (pair == NULL || pair == sc ||
(gdb) n
3880			printf("sc=%p\n", sc); fflush(stdout);
(gdb) n
sc=0x1046f10
3881			printf("sc->name=%p\n", sc->name); fflush(stdout);
(gdb) n
sc->name=0x6c66202c786c3830
3882			printf("sc->nr_args=%d, sc->args=%p\n", sc->nr_args, sc->args); fflush(stdout);
(gdb) p sc->nr_args
$10 = 1935635045
(gdb) p sc->args
$11 = (struct tep_format_field *) 0x257830203a6e656c
(gdb) p *sc
$12 = {e_machine = 540697702, id = 807761968, tp_format = 0x657075202c786c38, nr_args = 1935635045, args_size = 1634427759, bpf_prog = {sys_enter = 0x257830203a726464, 
    sys_exit = 0x7075202c786c3830}, is_exit = 101, is_open = 101, nonexistent = 114, use_btf = 95, args = 0x257830203a6e656c, 
  name = 0x6c66202c786c3830 <error: Cannot access memory at address 0x6c66202c786c3830>, fmt = 0x257830203a736761, arg_fmt = 0x786c3830}
(gdb) 

Ok, ran out of time, but if I simple avoid the second loop in:

static int trace__init_syscalls_bpf_prog_array_maps(struct trace *trace, int e_machine)


I.e. the one that starts with:

        /*
         * Now lets do a second pass looking for enabled syscalls without
         * an augmenter that have a signature that is a superset of another
         * syscall with an augmenter so that we can auto-reuse it.

This:

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index e0434f7dc67cb988..3664bb512c70cabf 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -3989,6 +3989,8 @@ static int trace__init_syscalls_bpf_prog_array_maps(struct trace *trace, int e_m
                        goto out;
        }
 
+       return 0;
+
        /*
         * Now lets do a second pass looking for enabled syscalls without
         * an augmenter that have a signature that is a superset of another
⬢ [acme@...lbox perf-tools-next]$ 


Then all works, we don't reuse any BPF program, but then that is an
heuristic anyway, that is tried becuase landlock_add_rule has a pointer
argument:

root@...ber:~# perf trace -e landlock_add_rule perf test -w landlock
     0.000 ( 0.003 ms): perf/71034 landlock_add_rule(ruleset_fd: 11, rule_type: LANDLOCK_RULE_PATH_BENEATH, rule_attr: 0x7fff6f2bb550, flags: 45) = -1 EINVAL (Invalid argument)
     0.004 ( 0.001 ms): perf/71034 landlock_add_rule(ruleset_fd: 11, rule_type: LANDLOCK_RULE_NET_PORT, rule_attr: 0x7fff6f2bb540, flags: 45) = -1 EINVAL (Invalid argument)
root@...ber:~# perf test enum
105: perf trace enum augmentation tests                              : Ok
root@...ber:~#

So its some sort of syncronization on the various new tables, sorted by
name, etc that then when iterating over the syscalls ends up using a sc
that is not initialized.

- Arnaldo