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

[Alexei Starovoitov]

On Wed, Nov 27, 2019 at 5:45 AM Arnaldo Carvalho de Melo
<acme@xxxxxxxxxx> wrote:
>
> Another fix I'm carrying in my perf/core branch,
>
> Regards,
>
> - Arnaldo
>
> commit 98bb09f90a0ae33125fabc8f41529345382f1498
> Author: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> 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@xxxxxxxxxx>
>     Cc: Andrii Nakryiko <andriin@xxxxxx>
>     Link: https://lkml.kernel.org/n/tip-iabs1wq19c357bkk84p7blif@xxxxxxxxxxxxxx
>     Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
>
> 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) ?