Re: [PATCH] libbpf: Use PRIu64 for sym->st_value to fix build on 32-bit arches

Alexei Starovoitov
2019-11-27T19:33:16Z

On Wed, Nov 27, 2019 at 5:45 AM Arnaldo Carvalho de Melo
<acme@kernel.org> wrote:
>
> Another fix I'm carrying in my perf/core branch,
>
> Regards,
>
> - Arnaldo
>
> commit 98bb09f90a0ae33125fabc8f41529345382f1498
> Author: Arnaldo Carvalho de Melo <acme@redhat.com>
> Date: Wed Nov 27 09:26:54 2019 -0300
>
> libbpf: Use PRIu64 for sym->st_value to fix build on 32-bit arches
>
> The st_value field is a 64-bit value, so use PRIu64 to fix this error on
> 32-bit arches:
>
> In file included from libbpf.c:52:
> libbpf.c: In function 'bpf_program__record_reloc':
> libbpf_internal.h:59:22: error: format '%lu' expects argument of type 'long unsigned int', but argument 3 has type 'Elf64_Addr' {aka 'const long long unsigned int'} [-Werror=format=]
> libbpf_print(level, "libbpf: " fmt, ##__VA_ARGS__); \
> ^~~~~~~~~~
> libbpf_internal.h:62:27: note: in expansion of macro '__pr'
> #define pr_warn(fmt, ...) __pr(LIBBPF_WARN, fmt, ##__VA_ARGS__)
> ^~~~
> libbpf.c:1822:4: note: in expansion of macro 'pr_warn'
> pr_warn("bad call relo offset: %lu\n", sym->st_value);
> ^~~~~~~
> libbpf.c:1822:37: note: format string is defined here
> pr_warn("bad call relo offset: %lu\n", sym->st_value);
> ~~^
> %llu
>
> Fixes: 1f8e2bcb2cd5 ("libbpf: Refactor relocation handling")
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: Andrii Nakryiko <andriin@fb.com>
> Link: https://lkml.kernel.org/n/tip-iabs1wq19c357bkk84p7blif@git.kernel.org
> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index b20f82e58989..6b0eae5c8a94 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -1819,7 +1819,7 @@ static int bpf_program__record_reloc(struct bpf_program *prog,
> return -LIBBPF_ERRNO__RELOC;
> }
> if (sym->st_value % 8) {
> - pr_warn("bad call relo offset: %lu\n", sym->st_value);
> + pr_warn("bad call relo offset: %" PRIu64 "\n", sym->st_value);

Looking at this more... I never liked this PRI stuff. It makes for
such unreadable code.
How about just typecasting st_value to (long) ?