Re: [RFT] Testing 1.22

[Jiri Olsa <jolsa@redhat.com>]

On Fri, May 28, 2021 at 04:45:31PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Thu, May 27, 2021 at 01:41:13PM -0700, Andrii Nakryiko escreveu:
> > On Thu, May 27, 2021 at 12:57 PM Arnaldo <arnaldo.melo@gmail.com> wrote:
> > > On May 27, 2021 4:14:17 PM GMT-03:00, Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:
> > > >If we make 1.22 mandatory there will be no good reason to make 1.23
> > > >mandatory again. So I will have absolutely no inclination to work on
> > > >this, for example. So we are just wasting a chance to clean up the
> > > >Kbuild story w.r.t. pahole. And we are talking about just a few days
> > > >at most, while we do have a reasonable work around on the kernel side.
> 
> > > So there were patches for stop using objcopy, which we thought could
> > > uncover some can of worms, were there patches for the detached BTF
> > > file?
>  
> > No, there weren't, if I remember correctly. What's the concern,
> > though? That detached BTF file isn't even an ELF, so it's
> > btf__get_raw_data() and write it to the file. Done.
> 
> See patch below, lightly tested, now working on making pahole accept raw
> BTF files out of /sys/kernel/btf/
> 
> Please test, and if works as expected, try to bolt this into the kbuild
> process, as intended.
> 
> - Arnaldo
> 
> commit b579a18a1ea0ee84b90b5302f597dda2edf2f61b
> Author: Arnaldo Carvalho de Melo <acme@redhat.com>
> Date:   Fri May 28 16:41:30 2021 -0300
> 
>     pahole: Allow encoding BTF into a detached file
>     
>     Previously the newly encoded BTF info was stored into a ELF section in
>     the file where the DWARF info was obtained, but it is useful to just
>     dump it into a separate file, do it.
>     
>     Requested-by: Andrii Nakryiko <andrii@kernel.org>
>     Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> 
> diff --git a/btf_encoder.c b/btf_encoder.c
> index 033c927b537dad1e..bc3ac72968cea826 100644
> --- a/btf_encoder.c
> +++ b/btf_encoder.c
> @@ -21,6 +21,14 @@
>  #include <stdlib.h> /* for qsort() and bsearch() */
>  #include <inttypes.h>
>  
> +#include <sys/types.h>
> +#include <sys/stat.h>
> +#include <fcntl.h>
> +
> +#include <unistd.h>
> +
> +#include <errno.h>
> +
>  /*
>   * This corresponds to the same macro defined in
>   * include/linux/kallsyms.h
> @@ -267,14 +275,62 @@ static struct btf_elf *btfe;
>  static uint32_t array_index_id;
>  static bool has_index_type;
>  
> -int btf_encoder__encode()
> +static int btf_encoder__dump(struct btf *btf, const char *filename)
> +{
> +	uint32_t raw_btf_size;
> +	const void *raw_btf_data;
> +	int fd, err;
> +
> +	/* Empty file, nothing to do, so... done! */
> +	if (btf__get_nr_types(btf) == 0)
> +		return 0;
> +
> +	if (btf__dedup(btf, NULL, NULL)) {
> +		fprintf(stderr, "%s: btf__dedup failed!\n", __func__);
> +		return -1;
> +	}
> +
> +	raw_btf_data = btf__get_raw_data(btf, &raw_btf_size);
> +	if (raw_btf_data == NULL) {
> +                fprintf(stderr, "%s: btf__get_raw_data failed!\n", __func__);
> +		return -1;
> +	}
> +
> +	fd = open(filename, O_WRONLY | O_CREAT);

I think you need to specify file mode as 3rd param:

	$ ./pahole -j krava vmlinux 
	$ ~/linux/tools/bpf/bpftool/bpftool btf dump file ./krava 
	Error: failed to load BTF from ./krava: Permission denied
	$ ll krava 
	--w-r-Sr-T. 1 jolsa jolsa 4525734 May 30 23:38 krava

jirka