linux-kernel - [PATCH 2/2] bpf: add bpf_probe_read

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Date:   Wed, 17 May 2023 14:56:09 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        John Fastabend <john.fastabend@...il.com>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Delyan Kratunov <delyank@...com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Menglong Dong <imagedong@...cent.com>,
        Yafang Shao <laoar.shao@...il.com>, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] bpf: add bpf_probe_read_kernel declaration

From: Arnd Bergmann <arnd@...db.de>

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]

Add a prototype directly in front of the function instead to shut
up the warning. Also, to avoid having an incompatible function override
the __weak definition, use an #ifdef to ensure that only one of the
two is ever defined.

I'm not sure what can be done to make the two prototypes match.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 kernel/bpf/core.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 6f5ede31e471..38762a784b86 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1635,11 +1635,14 @@ bool bpf_opcode_in_insntable(u8 code)
 }
 
 #ifndef CONFIG_BPF_JIT_ALWAYS_ON
-u64 __weak bpf_probe_read_kernel(void *dst, u32 size, const void *unsafe_ptr)
+u64 bpf_probe_read_kernel(void *dst, u32 size, const void *unsafe_ptr);
+#ifndef CONFIG_BPF_EVENTS
+u64 bpf_probe_read_kernel(void *dst, u32 size, const void *unsafe_ptr)
 {
 	memset(dst, 0, size);
 	return -EFAULT;
 }
+#endif
 
 /**
  *	___bpf_prog_run - run eBPF program on a given context
-- 
2.39.2