Subject: Re: [PATCH bpf] libbpf: Fix compile error in libbpf_attach_type_by_name

From: Arnaldo Carvalho de Melo <[email-masked]>
Date: Wed, 31 Oct 2018 17:49:57 -0300

Em Wed, Oct 31, 2018 at 12:57:18PM -0700, Andrey Ignatov escreveu:
> Arnaldo Carvalho de Melo reported build error in libbpf when clang
> version 3.8.1-24 (tags/RELEASE_381/final) is used:
> 
> libbpf.c:2201:36: error: comparison of constant -22 with expression of
> type 'const enum bpf_attach_type' is always false
> [-Werror,-Wtautological-constant-out-of-range-compare]
>                 if (section_names[i].attach_type == -EINVAL)
>                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^  ~~~~~~~
> 1 error generated.
> 
> Fix the error by keeping "is_attachable" property of a program in a
> separate struct field instead of trying to use attach_type itself.

Thanks, now it builds in all the previously failing systems:

# export PERF_TARBALL=http://192.168.86.4/perf/perf-4.19.0.tar.xz
# dm debian:9 fedora:25 fedora:26 fedora:27 ubuntu:16.04 ubuntu:17.10
   1 debian:9        : Ok   gcc (Debian 6.3.0-18+deb9u1) 6.3.0 20170516          clang version 3.8.1-24 (tags/RELEASE_381/final)
   2 fedora:25       : Ok   gcc (GCC) 6.4.1 20170727 (Red Hat 6.4.1-1)           clang version 3.9.1 (tags/RELEASE_391/final)
   3 fedora:26       : Ok   gcc (GCC) 7.3.1 20180130 (Red Hat 7.3.1-2)           clang version 4.0.1 (tags/RELEASE_401/final)
   4 fedora:27       : Ok   gcc (GCC) 7.3.1 20180712 (Red Hat 7.3.1-6)           clang version 5.0.2 (tags/RELEASE_502/final)
   5 ubuntu:16.04    : Ok   gcc (Ubuntu 5.4.0-6ubuntu1~16.04.10) 5.4.0 20160609  clang version 3.8.0-2ubuntu4 (tags/RELEASE_380/final)
   6 ubuntu:17.10    : Ok   gcc (Ubuntu 7.2.0-8ubuntu3.2) 7.2.0                  clang version 4.0.1-6 (tags/RELEASE_401/final)
#

Tested-by: Arnaldo Carvalho de Melo <[email-masked]>

I also have it tentatively applied to my perf/urgent branch, that I'll
push upstream soon.

- Arnaldo
 
> Fixes: commit 956b620fcf0b ("libbpf: Introduce libbpf_attach_type_by_name")
> Reported-by: Arnaldo Carvalho de Melo <[email-masked]>
> Signed-off-by: Andrey Ignatov <[email-masked]>
> ---
>  tools/lib/bpf/libbpf.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index b607be7236d3..d6e62e90e8d4 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -2084,19 +2084,19 @@ void bpf_program__set_expected_attach_type(struct bpf_program *prog,
>  	prog->expected_attach_type = type;
>  }
>  
> -#define BPF_PROG_SEC_IMPL(string, ptype, eatype, atype) \
> -	{ string, sizeof(string) - 1, ptype, eatype, atype }
> +#define BPF_PROG_SEC_IMPL(string, ptype, eatype, is_attachable, atype) \
> +	{ string, sizeof(string) - 1, ptype, eatype, is_attachable, atype }
>  
>  /* Programs that can NOT be attached. */
> -#define BPF_PROG_SEC(string, ptype) BPF_PROG_SEC_IMPL(string, ptype, 0, -EINVAL)
> +#define BPF_PROG_SEC(string, ptype) BPF_PROG_SEC_IMPL(string, ptype, 0, 0, 0)
>  
>  /* Programs that can be attached. */
>  #define BPF_APROG_SEC(string, ptype, atype) \
> -	BPF_PROG_SEC_IMPL(string, ptype, 0, atype)
> +	BPF_PROG_SEC_IMPL(string, ptype, 0, 1, atype)
>  
>  /* Programs that must specify expected attach type at load time. */
>  #define BPF_EAPROG_SEC(string, ptype, eatype) \
> -	BPF_PROG_SEC_IMPL(string, ptype, eatype, eatype)
> +	BPF_PROG_SEC_IMPL(string, ptype, eatype, 1, eatype)
>  
>  /* Programs that can be attached but attach type can't be identified by section
>   * name. Kept for backward compatibility.
> @@ -2108,6 +2108,7 @@ static const struct {
>  	size_t len;
>  	enum bpf_prog_type prog_type;
>  	enum bpf_attach_type expected_attach_type;
> +	int is_attachable;
>  	enum bpf_attach_type attach_type;
>  } section_names[] = {
>  	BPF_PROG_SEC("socket",			BPF_PROG_TYPE_SOCKET_FILTER),
> @@ -2198,7 +2199,7 @@ int libbpf_attach_type_by_name(const char *name,
>  	for (i = 0; i < ARRAY_SIZE(section_names); i++) {
>  		if (strncmp(name, section_names[i].sec, section_names[i].len))
>  			continue;
> -		if (section_names[i].attach_type == -EINVAL)
> +		if (!section_names[i].is_attachable)
>  			return -EINVAL;
>  		*attach_type = section_names[i].attach_type;
>  		return 0;
> -- 
> 2.17.1