linux-kernel - [PATCH v2] bpf: Use correct #ifdef controller for trace_call

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Message-ID: <1435408561-24080-1-git-send-email-wangnan0@huawei.com>
Date:	Sat, 27 Jun 2015 12:36:01 +0000
From:	Wang Nan <wangnan0@...wei.com>
To:	<acme@...nel.org>, <ast@...mgrid.com>, <brendan.d.gregg@...il.com>,
	<daniel@...earbox.net>, <namhyung@...nel.org>,
	<masami.hiramatsu.pt@...achi.com>, <paulus@...ba.org>,
	<a.p.zijlstra@...llo.nl>, <mingo@...hat.com>, <jolsa@...nel.org>,
	<dsahern@...il.com>
CC:	<linux-kernel@...r.kernel.org>, <lizefan@...wei.com>,
	<hekuang@...wei.com>, <xiakaixu@...wei.com>, <pi3orama@....com>
Subject: [PATCH v2] bpf: Use correct #ifdef controller for trace_call_bpf()

Commit e1abf2cc8d5d80b41c4419368ec743ccadbb131e ("bpf: Fix the build on
BPF_SYSCALL=y && !CONFIG_TRACING kernels, make it more configurable")
updated the building condition of bpf_trace.o from CONFIG_BPF_SYSCALL
to CONFIG_BPF_EVENTS, but the corresponding #ifdef controller in
ftrace_event.h for trace_call_bpf() is not changed. Which, in theory,
is incorrect.

With current Kconfigs, we can create a .config with CONFIG_BPF_SYSCALL=y
and CONFIG_BPF_EVENTS=n by unselecting CONFIG_KPROBE_EVENT and
selecting CONFIG_BPF_SYSCALL. With these options, trace_call_bpf() will
be defined as an extern function, but if anyone calls it a symbol missing
error will be trigger since bpf_trace.o is not build.

This patch changes the #ifdef controller for trace_call_bpf() from
CONFIG_BPF_SYSCALL to CONFIG_BPF_EVENTS. I'll show its correctness:

Before this patch:

   BPF_SYSCALL   BPF_EVENTS   trace_call_bpf   bpf_trace.o
   y             y           normal           compiled
   n             n           inline           not compiled
   y             n           normal           not compiled (incorrect)
   n             y          impossible (BPF_EVENTS depends on BPF_SYSCALL)

After this patch:

   BPF_SYSCALL   BPF_EVENTS   trace_call_bpf   bpf_trace.o
   y             y           normal           compiled
   n             n           inline           not compiled
   y             n           inline           not compiled (fixed)
   n             y          impossible (BPF_EVENTS depends on BPF_SYSCALL)

So this patch doesn't break thing. QED.

Signed-off-by: Wang Nan <wangnan0@...wei.com>
---

v1 is incorrect: lost the 'S' in 'CONFIG_BPF_EVENTS'. Please ignore it.

---
 include/linux/ftrace_event.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index f9ecf63..ec48c92 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -553,7 +553,7 @@ event_trigger_unlock_commit_regs(struct ftrace_event_file *file,
 		event_triggers_post_call(file, tt);
 }

-#ifdef CONFIG_BPF_SYSCALL
+#ifdef CONFIG_BPF_EVENTS
 unsigned int trace_call_bpf(struct bpf_prog *prog, void *ctx);
 #else
 static inline unsigned int trace_call_bpf(struct bpf_prog *prog, void *ctx)
-- 
1.8.3.4

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