Re: [PATCH] [v5] bpf: fix bpf_probe_read_kernel prototype mismatch

[Yonghong Song]

On 8/1/23 4:13 AM, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
>
> bpf_probe_read_kernel() has a __weak definition in core.c and another
> definition with an incompatible prototype in kernel/trace/bpf_trace.c,
> when CONFIG_BPF_EVENTS is enabled.
>
> Since the two are incompatible, there cannot be a shared declaration in
> a header file, but the lack of a prototype causes a W=1 warning:
>
> kernel/bpf/core.c:1638:12: error: no previous prototype for 'bpf_probe_read_kernel' [-Werror=missing-prototypes]
>
> On 32-bit architectures, the local prototype
>
> u64 __weak bpf_probe_read_kernel(void *dst, u32 size, const void *unsafe_ptr)
>
> passes arguments in other registers as the one in bpf_trace.c
>
> BPF_CALL_3(bpf_probe_read_kernel, void *, dst, u32, size,
>              const void *, unsafe_ptr)
>
> which uses 64-bit arguments in pairs of registers.
>
> As both versions of the function are fairly simple and only really
> differ in one line, just move them into a header file as an inline
> function that does not add any overhead for the bpf_trace.c callers
> and actually avoids a function call for the other one.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Link: https://lore.kernel.org/all/ac25cb0f-b804-1649-3afb-1dc6138c2716@xxxxxxxxxxxxx/
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>

Acked-by: Yonghong Song <yonghong.song@xxxxxxxxx>