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

From: Yonghong Song
Date: Tue Aug 01 2023 - 10:41:41 EST

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
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>

Acked-by: Yonghong Song <>