Subject: Re: [PATCH perf 3/3] tools/perf: recognize and process RECORD_MMAP events for bpf progs

From: Arnaldo Carvalho de Melo <[email-masked]>
Date: Thu, 20 Sep 2018 10:36:17 -0300

Em Wed, Sep 19, 2018 at 03:39:35PM -0700, Alexei Starovoitov escreveu:
> Recognize JITed bpf prog load/unload events.
> Add/remove kernel symbols accordingly.
> 
> Signed-off-by: Alexei Starovoitov <[email-masked]>
> ---
>  tools/perf/util/machine.c | 27 +++++++++++++++++++++++++++
>  tools/perf/util/symbol.c  | 13 +++++++++++++
>  tools/perf/util/symbol.h  |  1 +
>  3 files changed, 41 insertions(+)
> 
> diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> index c4acd2001db0..ae4f8a0fdc7e 100644
> --- a/tools/perf/util/machine.c
> +++ b/tools/perf/util/machine.c
> @@ -25,6 +25,7 @@
>  #include "sane_ctype.h"
>  #include <symbol/kallsyms.h>
>  #include <linux/mman.h>
> +#include <linux/magic.h>
>  
>  static void __machine__remove_thread(struct machine *machine, struct thread *th, bool lock);
>  
> @@ -1460,6 +1461,32 @@ static int machine__process_kernel_mmap_event(struct machine *machine,
>  	enum dso_kernel_type kernel_type;
>  	bool is_kernel_mmap;
>  
> +	/* process JITed bpf programs load/unload events */
> +	if (event->mmap.pid == ~0u && event->mmap.tid == BPF_FS_MAGIC) {

So, this would be in machine__process_kernel_munmap-event(machine), etc,
no check for BPF_FS_MAGIC would be needed with a PERF_RECORD_MUNMAP.

> +		struct symbol *sym;
> +		u64 ip;
> +
> +		map = map_groups__find(&machine->kmaps, event->mmap.start);
> +		if (!map) {
> +			pr_err("No kernel map for IP %lx\n", event->mmap.start);
> +			goto out_problem;
> +		}
> +		ip = event->mmap.start - map->start + map->pgoff;
> +		if (event->mmap.filename[0]) {
> +			sym = symbol__new(ip, event->mmap.len, 0, 0,
> +					  event->mmap.filename);

Humm, so the bpf program would be just one symbol... bpf-to-bpf calls
will be to a different bpf program, right? 

/me goes to read https://lwn.net/Articles/741773/
                 "[PATCH bpf-next 00/13] bpf: introduce function calls"

> +			dso__insert_symbol(map->dso, sym);
> +		} else {
> +			if (symbols__erase(&map->dso->symbols, ip)) {
> +				pr_err("No bpf prog at IP %lx/%lx\n",
> +				       event->mmap.start, ip);
> +				goto out_problem;
> +			}
> +			dso__reset_find_symbol_cache(map->dso);
> +		}
> +		return 0;
> +	}
> +
>  	/* If we have maps from kcore then we do not need or want any others */
>  	if (machine__uses_kcore(machine))
>  		return 0;
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index d188b7588152..0653f313661d 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -353,6 +353,19 @@ static struct symbol *symbols__find(struct rb_root *symbols, u64 ip)
>  	return NULL;
>  }
>  
> +int symbols__erase(struct rb_root *symbols, u64 ip)
> +{
> +	struct symbol *s;
> +
> +	s = symbols__find(symbols, ip);
> +	if (!s)
> +		return -ENOENT;
> +
> +	rb_erase(&s->rb_node, symbols);
> +	symbol__delete(s);
> +	return 0;
> +}
> +
>  static struct symbol *symbols__first(struct rb_root *symbols)
>  {
>  	struct rb_node *n = rb_first(symbols);
> diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
> index f25fae4b5743..92ef31953d9a 100644
> --- a/tools/perf/util/symbol.h
> +++ b/tools/perf/util/symbol.h
> @@ -310,6 +310,7 @@ char *dso__demangle_sym(struct dso *dso, int kmodule, const char *elf_name);
>  
>  void __symbols__insert(struct rb_root *symbols, struct symbol *sym, bool kernel);
>  void symbols__insert(struct rb_root *symbols, struct symbol *sym);
> +int symbols__erase(struct rb_root *symbols, u64 ip);
>  void symbols__fixup_duplicate(struct rb_root *symbols);
>  void symbols__fixup_end(struct rb_root *symbols);
>  void map_groups__fixup_end(struct map_groups *mg);
> -- 
> 2.17.1