linux-kernel - Re: [PATCH] selftests/bpf: Fix conflicts with built-in functions in bpf_iter

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Date:   Fri, 26 Aug 2022 21:55:38 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     James Hilliard <james.hilliard1@...il.com>
Cc:     bpf@...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>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>,
        Alan Maguire <alan.maguire@...cle.com>,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests/bpf: Fix conflicts with built-in functions in bpf_iter_ksym

On Thu, Aug 25, 2022 at 6:26 PM James Hilliard
<james.hilliard1@...il.com> wrote:
>
> Both tolower and toupper are built in c functions, we should not

Really? How come? Can you point out where this is specified in C
standard? From what I can tell you have to include <ctype.h> to get
toupper()/tolower().

This seems like yet another GCC-BPF quirk?

> redefine them as this can result in a build error.
>
> Fixes the following errors:
> progs/bpf_iter_ksym.c:10:20: error: conflicting types for built-in function 'tolower'; expected 'int(int)' [-Werror=builtin-declaration-mismatch]
>    10 | static inline char tolower(char c)
>       |                    ^~~~~~~
> progs/bpf_iter_ksym.c:5:1: note: 'tolower' is declared in header '<ctype.h>'
>     4 | #include <bpf/bpf_helpers.h>
>   +++ |+#include <ctype.h>
>     5 |
> progs/bpf_iter_ksym.c:17:20: error: conflicting types for built-in function 'toupper'; expected 'int(int)' [-Werror=builtin-declaration-mismatch]
>    17 | static inline char toupper(char c)
>       |                    ^~~~~~~
> progs/bpf_iter_ksym.c:17:20: note: 'toupper' is declared in header '<ctype.h>'
>
> Signed-off-by: James Hilliard <james.hilliard1@...il.com>
> ---
>  tools/testing/selftests/bpf/progs/bpf_iter_ksym.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_ksym.c b/tools/testing/selftests/bpf/progs/bpf_iter_ksym.c
> index 285c008cbf9c..9ba14c37bbcc 100644
> --- a/tools/testing/selftests/bpf/progs/bpf_iter_ksym.c
> +++ b/tools/testing/selftests/bpf/progs/bpf_iter_ksym.c
> @@ -7,14 +7,14 @@ char _license[] SEC("license") = "GPL";
>
>  unsigned long last_sym_value = 0;
>
> -static inline char tolower(char c)
> +static inline char to_lower(char c)
>  {
>         if (c >= 'A' && c <= 'Z')
>                 c += ('a' - 'A');
>         return c;
>  }
>
> -static inline char toupper(char c)
> +static inline char to_upper(char c)
>  {
>         if (c >= 'a' && c <= 'z')
>                 c -= ('a' - 'A');
> @@ -54,7 +54,7 @@ int dump_ksym(struct bpf_iter__ksym *ctx)
>         type = iter->type;
>
>         if (iter->module_name[0]) {
> -               type = iter->exported ? toupper(type) : tolower(type);
> +               type = iter->exported ? to_upper(type) : to_lower(type);
>                 BPF_SEQ_PRINTF(seq, "0x%llx %c %s [ %s ] ",
>                                value, type, iter->name, iter->module_name);
>         } else {
> --
> 2.34.1
>