Re: [PATCH] bpftool: Try to read btf as raw data if elf read fails

Jiri Olsa
2019-10-21T14:02:44Z

On Fri, Oct 18, 2019 at 03:39:05PM -0700, Jakub Kicinski wrote:
> On Fri, 18 Oct 2019 12:34:04 +0200, Jiri Olsa wrote:
> > The bpftool interface stays the same, but now it's possible
> > to run it over BTF raw data, like:
> >
> > $ bpftool btf dump file /sys/kernel/btf/vmlinux
> > libbpf: failed to get EHDR from /sys/kernel/btf/vmlinux
> > [1] INT '(anon)' size=4 bits_offset=0 nr_bits=32 encoding=(none)
> > [2] INT 'long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none)
> > [3] CONST '(anon)' type_id=2
> >
> > I'm also adding err init to 0 because I was getting uninitialized
> > warnings from gcc.
> >
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> > tools/bpf/bpftool/btf.c | 47 ++++++++++++++++++++++++++++++++++++-----
> > 1 file changed, 42 insertions(+), 5 deletions(-)
> >
> > diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
> > index 9a9376d1d3df..100fb7e02329 100644
> > --- a/tools/bpf/bpftool/btf.c
> > +++ b/tools/bpf/bpftool/btf.c
> > @@ -12,6 +12,9 @@
> > #include <libbpf.h>
> > #include <linux/btf.h>
> > #include <linux/hashtable.h>
> > +#include <sys/types.h>
> > +#include <sys/stat.h>
> > +#include <unistd.h>
> >
> > #include "btf.h"
> > #include "json_writer.h"
> > @@ -388,6 +391,35 @@ static int dump_btf_c(const struct btf *btf,
> > return err;
> > }
> >
> > +static struct btf *btf__parse_raw(const char *file)
> > +{
> > + struct btf *btf = ERR_PTR(-EINVAL);
> > + __u8 *buf = NULL;
>
> Please drop the inits
>
> > + struct stat st;
> > + FILE *f;
> > +
> > + if (stat(file, &st))
> > + return btf;
>
> And return constants here
>
> > + f = fopen(file, "rb");
> > + if (!f)
> > + return btf;
>
> and here
>
> > + buf = malloc(st.st_size);
> > + if (!buf)
> > + goto err;
>
> and jump to the right place here.
>
> > + if ((size_t) st.st_size != fread(buf, 1, st.st_size, f))
> > + goto err;
> > +
> > + btf = btf__new(buf, st.st_size);
> > +
> > +err:
>
> The prefix for error labels which is shared with non-error path is exit_
>
> > + free(buf);
> > + fclose(f);
> > + return btf;
> > +}
> > +

ok for all above

> > static int do_dump(int argc, char **argv)
> > {
> > struct btf *btf = NULL;
> > @@ -397,7 +429,7 @@ static int do_dump(int argc, char **argv)
> > __u32 btf_id = -1;
> > const char *src;
> > int fd = -1;
> > - int err;
> > + int err = 0;
>
> This change looks unnecessary.

I'm getting confusing warnings from gcc about this,
but there is a code path where do_dump would return
untouched err:

do_dump
int err;

} else if (is_prefix(src, "file")) {
btf = btf__parse_elf(*argv, NULL); // succeeds

}

while (argc) {
if (is_prefix(*argv, "format")) {
else { // in here
goto done;
}

done:
return err;

thanks,
jirka