Re: [PATCH bpf-next v1 12/19] bpf: add bpf_seq_printf and bpf_seq_write helpers

[Yonghong Song <yhs@fb.com>]

On 4/27/20 11:02 PM, kbuild test robot wrote:
> Hi Yonghong,
> 
> I love your patch! Perhaps something to improve:
> 
> [auto build test WARNING on bpf-next/master]
> [cannot apply to bpf/master net/master vhost/linux-next net-next/master linus/master v5.7-rc3 next-20200424]
> [if your patch is applied to the wrong git tree, please drop us a note to help
> improve the system. BTW, we also suggest to use '--base' option to specify the
> base tree in git format-patch, please see https://urldefense.proofpoint.com/v2/url?u=https-3A__stackoverflow.com_a_37406982&d=DwIBAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=ecuvAWhErc8x32mTscXvNhgSPkwcM7tK05lEVYIQMbI&s=rUkkN8hfXpHttD7t9NCfe5OIFTZZ_cn_SQTDjvs1cj0&e= ]
> 
> url:    https://github.com/0day-ci/linux/commits/Yonghong-Song/bpf-implement-bpf-iterator-for-kernel-data/20200428-115101
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
> config: sh-allmodconfig (attached as .config)
> compiler: sh4-linux-gcc (GCC) 9.3.0
> reproduce:
>          wget https://urldefense.proofpoint.com/v2/url?u=https-3A__raw.githubusercontent.com_intel_lkp-2Dtests_master_sbin_make.cross&d=DwIBAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=ecuvAWhErc8x32mTscXvNhgSPkwcM7tK05lEVYIQMbI&s=mm3zd05JFgyD1Fvvg5yehcYq7d9KLZkN7XSYyLaJRkA&e=  -O ~/bin/make.cross
>          chmod +x ~/bin/make.cross
>          # save the attached .config to linux build tree
>          COMPILER_INSTALL_PATH=$HOME/0day GCC_VERSION=9.3.0 make.cross ARCH=sh
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kbuild test robot <lkp@intel.com>
> 
> All warnings (new ones prefixed by >>):
> 
>     In file included from kernel/trace/bpf_trace.c:10:
>     kernel/trace/bpf_trace.c: In function 'bpf_seq_printf':
>>> kernel/trace/bpf_trace.c:463:35: warning: the frame size of 1672 bytes is larger than 1024 bytes [-Wframe-larger-than=]
>       463 | BPF_CALL_5(bpf_seq_printf, struct seq_file *, m, char *, fmt, u32, fmt_size,

Thanks for reporting. Currently, I am supporting up to 12 string format 
specifiers and each string up to 128 bytes. To avoid racing and helper 
memory allocation, I put it on stack hence the above 1672 bytes, but
practically, I think support 4 strings with 128 bytes each is enough.
I will make a change in the next revision.

>           |                                   ^~~~~~~~
>     include/linux/filter.h:456:30: note: in definition of macro '__BPF_CAST'
>       456 |           (unsigned long)0, (t)0))) a
>           |                              ^
>>> include/linux/filter.h:449:27: note: in expansion of macro '__BPF_MAP_5'
>       449 | #define __BPF_MAP(n, ...) __BPF_MAP_##n(__VA_ARGS__)
>           |                           ^~~~~~~~~~
>>> include/linux/filter.h:474:35: note: in expansion of macro '__BPF_MAP'
>       474 |   return ((btf_##name)____##name)(__BPF_MAP(x,__BPF_CAST,__BPF_N,__VA_ARGS__));\
>           |                                   ^~~~~~~~~
>>> include/linux/filter.h:484:31: note: in expansion of macro 'BPF_CALL_x'
>       484 | #define BPF_CALL_5(name, ...) BPF_CALL_x(5, name, __VA_ARGS__)
>           |                               ^~~~~~~~~~
>>> kernel/trace/bpf_trace.c:463:1: note: in expansion of macro 'BPF_CALL_5'
>       463 | BPF_CALL_5(bpf_seq_printf, struct seq_file *, m, char *, fmt, u32, fmt_size,
>           | ^~~~~~~~~~
> 
> vim +463 kernel/trace/bpf_trace.c
> 
>     462	
>   > 463	BPF_CALL_5(bpf_seq_printf, struct seq_file *, m, char *, fmt, u32, fmt_size,
>     464		   const void *, data, u32, data_len)
>     465	{
>     466		char bufs[MAX_SEQ_PRINTF_VARARGS][MAX_SEQ_PRINTF_STR_LEN];
>     467		u64 params[MAX_SEQ_PRINTF_VARARGS];
>     468		int i, copy_size, num_args;
>     469		const u64 *args = data;
>     470		int fmt_cnt = 0;
>     471	
[...]