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bpf: Add dump_stack() analogue to print to BPF stderr

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Introduce a kernel function which is the analogue of dump_stack()
printing some useful information and the stack trace. This is not
exposed to BPF programs yet, but can be made available in the future.

When we have a program counter for a BPF program in the stack trace,
also additionally output the filename and line number to make the trace
helpful. The rest of the trace can be passed into ./decode_stacktrace.sh
to obtain the line numbers for kernel symbols.

Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20250703204818.925464-7-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Kumar Kartikeya Dwivedi 2025-07-03 13:48:12 -07:00 • committed by Alexei Starovoitov
parent f0c53fd4a7
commit d7c431cafc
2 changed files with 50 additions and 0 deletions
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2
include/linux/bpf.h
View file

@ -3616,8 +3616,10 @@ __printf(2, 3)
int bpf_stream_stage_printk(struct bpf_stream_stage *ss, const char *fmt, ...);
int bpf_stream_stage_commit(struct bpf_stream_stage *ss, struct bpf_prog *prog,
enum bpf_stream_id stream_id);
int bpf_stream_stage_dump_stack(struct bpf_stream_stage *ss);
#define bpf_stream_printk(ss, ...) bpf_stream_stage_printk(&ss, __VA_ARGS__)
#define bpf_stream_dump_stack(ss) bpf_stream_stage_dump_stack(&ss)
#define bpf_stream_stage(ss, prog, stream_id, expr) \
({ \

48
kernel/bpf/stream.c
View file

@ -2,6 +2,7 @@
/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
#include <linux/bpf.h>
#include <linux/filter.h>
#include <linux/bpf_mem_alloc.h>
#include <linux/percpu.h>
#include <linux/refcount.h>
@ -476,3 +477,50 @@ int bpf_stream_stage_commit(struct bpf_stream_stage *ss, struct bpf_prog *prog,
llist_add_batch(head, tail, &stream->log);
return 0;
}
struct dump_stack_ctx {
struct bpf_stream_stage *ss;
int err;
};
static bool dump_stack_cb(void *cookie, u64 ip, u64 sp, u64 bp)
{
struct dump_stack_ctx *ctxp = cookie;
const char *file = "", *line = "";
struct bpf_prog *prog;
int num, ret;
rcu_read_lock();
prog = bpf_prog_ksym_find(ip);
rcu_read_unlock();
if (prog) {
ret = bpf_prog_get_file_line(prog, ip, &file, &line, &num);
if (ret < 0)
goto end;
ctxp->err = bpf_stream_stage_printk(ctxp->ss, "%pS\n %s @ %s:%d\n",
(void *)ip, line, file, num);
return !ctxp->err;
}
end:
ctxp->err = bpf_stream_stage_printk(ctxp->ss, "%pS\n", (void *)ip);
return !ctxp->err;
}
int bpf_stream_stage_dump_stack(struct bpf_stream_stage *ss)
{
struct dump_stack_ctx ctx = { .ss = ss };
int ret;
ret = bpf_stream_stage_printk(ss, "CPU: %d UID: %d PID: %d Comm: %s\n",
raw_smp_processor_id(), __kuid_val(current_real_cred()->euid),
current->pid, current->comm);
if (ret)
return ret;
ret = bpf_stream_stage_printk(ss, "Call trace:\n");
if (ret)
return ret;
arch_bpf_stack_walk(dump_stack_cb, &ctx);
if (ctx.err)
return ctx.err;
return bpf_stream_stage_printk(ss, "\n");
}