[PATCH v2] libbpf: Fix build warning on ref_ctr_off

[PATCH v2] libbpf: Fix build warning on ref_ctr_off

[Khem Raj]

Clang warns on 32-bit ARM on this comparision

libbpf.c:10497:18: error: result of comparison of constant 4294967296 with expression of type 'size_t' (aka 'unsigned int') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
        if (ref_ctr_off >= (1ULL << PERF_UPROBE_REF_CTR_OFFSET_BITS))
            ~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

typecast ref_ctr_off to __u64 in the check conditional, it is false on 32bit anyways.

Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Song Liu <song@kernel.org>
Cc: Yonghong Song <yhs@fb.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>
---
v2: Typecast ref_ctr_off to __u64 instead of checking platform word size

 tools/lib/bpf/libbpf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 2a82f49ce16f..a5c67a3c93c5 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -9903,7 +9903,7 @@ static int perf_event_open_probe(bool uprobe, bool retprobe, const char *name,
 	char errmsg[STRERR_BUFSIZE];
 	int type, pfd;
 
-	if (ref_ctr_off >= (1ULL << PERF_UPROBE_REF_CTR_OFFSET_BITS))
+	if ((__u64)ref_ctr_off >= (1ULL << PERF_UPROBE_REF_CTR_OFFSET_BITS))
 		return -EINVAL;
 
 	memset(&attr, 0, attr_sz);
-- 
2.39.0

Re: [PATCH v2] libbpf: Fix build warning on ref_ctr_off

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Andrii Nakryiko <andrii@kernel.org>:

On Mon, 19 Dec 2022 11:15:26 -0800 you wrote:
> Clang warns on 32-bit ARM on this comparision
> 
> libbpf.c:10497:18: error: result of comparison of constant 4294967296 with expression of type 'size_t' (aka 'unsigned int') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
>         if (ref_ctr_off >= (1ULL << PERF_UPROBE_REF_CTR_OFFSET_BITS))
>             ~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> typecast ref_ctr_off to __u64 in the check conditional, it is false on 32bit anyways.
> 
> [...]

Here is the summary with links:
  - [v2] libbpf: Fix build warning on ref_ctr_off
    https://git.kernel.org/bpf/bpf-next/c/1520e8466d68

You are awesome, thank you!
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