netdev - Re: [PATCH bpf-next v1 6/8] selftests/bpf: Fix compile if backtrace support missing in libc

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Message-ID: <CAEf4Bza_y15T4gU=Kiu2d+RbWpxEzrLe6T71bCpK383xHD8JMg@mail.gmail.com>
Date: Thu, 25 Jul 2024 13:22:37 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Tony Ambardar <tony.ambardar@...il.com>
Cc: bpf@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	netdev@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>, 
	Björn Töpel <bjorn@...nel.org>, 
	Magnus Karlsson <magnus.karlsson@...el.com>, 
	Maciej Fijalkowski <maciej.fijalkowski@...el.com>, Jonathan Lemon <jonathan.lemon@...il.com>, 
	"David S. Miller" <davem@...emloft.net>, Yan Zhai <yan@...udflare.com>
Subject: Re: [PATCH bpf-next v1 6/8] selftests/bpf: Fix compile if backtrace
 support missing in libc

On Thu, Jul 25, 2024 at 3:39 AM Tony Ambardar <tony.ambardar@...il.com> wrote:
>
> From: Tony Ambardar <tony.ambardar@...il.com>
>
> Use backtrace functions only with glibc and otherwise provide stubs in
> test_progs.c. This avoids compile errors (e.g. with musl libc) like:
>
>   test_progs.c:13:10: fatal error: execinfo.h: No such file or directory
>      13 | #include <execinfo.h> /* backtrace */
>         |          ^~~~~~~~~~~~
>   test_progs.c: In function 'crash_handler':
>   test_progs.c:1034:14: error: implicit declaration of function 'backtrace' [-Werror=implicit-function-declaration]
>    1034 |         sz = backtrace(bt, ARRAY_SIZE(bt));
>         |              ^~~~~~~~~
>   test_progs.c:1045:9: error: implicit declaration of function 'backtrace_symbols_fd' [-Werror=implicit-function-declaration]
>    1045 |         backtrace_symbols_fd(bt, sz, STDERR_FILENO);
>         |         ^~~~~~~~~~~~~~~~~~~~
>
> Fixes: 9fb156bb82a3 ("selftests/bpf: Print backtrace on SIGSEGV in test_progs")
> Signed-off-by: Tony Ambardar <tony.ambardar@...il.com>
> ---
>  tools/testing/selftests/bpf/test_progs.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/bpf/test_progs.c b/tools/testing/selftests/bpf/test_progs.c
> index 60c5ec0f6abf..f6cfc6a8e8f0 100644
> --- a/tools/testing/selftests/bpf/test_progs.c
> +++ b/tools/testing/selftests/bpf/test_progs.c
> @@ -10,7 +10,6 @@
>  #include <sched.h>
>  #include <signal.h>
>  #include <string.h>
> -#include <execinfo.h> /* backtrace */
>  #include <sys/sysinfo.h> /* get_nprocs */
>  #include <netinet/in.h>
>  #include <sys/select.h>
> @@ -19,6 +18,14 @@
>  #include <bpf/btf.h>
>  #include "json_writer.h"
>
> +#ifdef __GLIBC__
> +#include <execinfo.h> /* backtrace */
> +#else
> +#define backtrace(...) (0)
> +#define backtrace_symbols_fd(bt, sz, fd) \
> +       dprintf(fd, "<backtrace not supported>\n", bt, sz)
> +#endif

First, let's define backtrace() and backtrace_symbols_fd() as proper
functions, not a macro?

And second, what if we then make those functions __weak, so they
provide default implementations if libc doesn't provide those
functions?

This parts seems unavoidable, though:

#ifdef __GLIBC__
#include <execinfo.h>
#endif


> +
>  static bool verbose(void)
>  {
>         return env.verbosity > VERBOSE_NONE;
> --
> 2.34.1
>