[PATCH net] perf/bpf: fix a clang compilation issue

[PATCH net] perf/bpf: fix a clang compilation issue

[Yonghong Song]

clang does not support variable length array for structure member.
It has the following error during compilation:

kernel/trace/trace_syscalls.c:568:17: error: fields must have a constant size:
'variable length array in structure' extension will never be supported
                unsigned long args[sys_data->nb_args];
                              ^

The fix is to use a fixed array length instead.

Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
---
 include/linux/syscalls.h      | 2 ++
 kernel/trace/trace_syscalls.c | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 88951b7..95606a2 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -200,6 +200,8 @@ static inline int is_syscall_trace_event(struct trace_event_call *tp_event)
 #define SYSCALL_DEFINE5(name, ...) SYSCALL_DEFINEx(5, _##name, __VA_ARGS__)
 #define SYSCALL_DEFINE6(name, ...) SYSCALL_DEFINEx(6, _##name, __VA_ARGS__)
 
+#define SYSCALL_DEFINE_MAXARGS	6
+
 #define SYSCALL_DEFINEx(x, sname, ...)				\
 	SYSCALL_METADATA(sname, x, __VA_ARGS__)			\
 	__SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index 9c4eef2..696afe7 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -565,7 +565,7 @@ static int perf_call_bpf_enter(struct bpf_prog *prog, struct pt_regs *regs,
 	struct syscall_tp_t {
 		unsigned long long regs;
 		unsigned long syscall_nr;
-		unsigned long args[sys_data->nb_args];
+		unsigned long args[SYSCALL_DEFINE_MAXARGS];
 	} param;
 	int i;
 
-- 
2.9.5

Re: [PATCH net] perf/bpf: fix a clang compilation issue

[David Miller]

From: Yonghong Song <yhs@fb.com>
Date: Thu, 7 Sep 2017 18:36:15 -0700

> clang does not support variable length array for structure member.
> It has the following error during compilation:
> 
> kernel/trace/trace_syscalls.c:568:17: error: fields must have a constant size:
> 'variable length array in structure' extension will never be supported
>                 unsigned long args[sys_data->nb_args];
>                               ^
> 
> The fix is to use a fixed array length instead.
> 
> Reported-by: Nick Desaulniers <ndesaulniers@google.com>
> Signed-off-by: Yonghong Song <yhs@fb.com>

Applied.

Re: [PATCH net] perf/bpf: fix a clang compilation issue

[Nick Desaulniers]

great, thanks!

On Mon, Sep 11, 2017 at 2:28 PM, David Miller <davem@davemloft.net> wrote:
> From: Yonghong Song <yhs@fb.com>
> Date: Thu, 7 Sep 2017 18:36:15 -0700
>
>> clang does not support variable length array for structure member.
>> It has the following error during compilation:
>>
>> kernel/trace/trace_syscalls.c:568:17: error: fields must have a constant size:
>> 'variable length array in structure' extension will never be supported
>>                 unsigned long args[sys_data->nb_args];
>>                               ^
>>
>> The fix is to use a fixed array length instead.
>>
>> Reported-by: Nick Desaulniers <ndesaulniers@google.com>
>> Signed-off-by: Yonghong Song <yhs@fb.com>
>
> Applied.



-- 
Thanks,
~Nick Desaulniers