linux-kernel - Re: [PATCH v5 perf,bpf 12/15] perf, bpf: enable annotation of bpf program

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Message-ID: <35B644D2-D4E4-4C97-A06D-8A4479F261C1@fb.com>
Date:   Mon, 4 Mar 2019 20:52:06 +0000
From:   Song Liu <songliubraving@...com>
To:     Jiri Olsa <jolsa@...hat.com>
CC:     Networking <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "acme@...hat.com" <acme@...hat.com>,
        "jolsa@...nel.org" <jolsa@...nel.org>,
        "namhyung@...nel.org" <namhyung@...nel.org>
Subject: Re: [PATCH v5 perf,bpf 12/15] perf, bpf: enable annotation of bpf
 program



> On Mar 4, 2019, at 5:53 AM, Jiri Olsa <jolsa@...hat.com> wrote:
> 
> On Wed, Feb 27, 2019 at 09:06:40PM -0800, Song Liu wrote:
> 
> SNIP
> 
>> +
>> +	disassemble_init_for_target(&info);
>> +
>> +#ifdef DISASM_FOUR_ARGS_SIGNATURE
>> +	disassemble = disassembler(info.arch,
>> +				   bfd_big_endian(bfdf),
>> +				   info.mach,
>> +				   bfdf);
>> +#else
>> +	disassemble = disassembler(bfdf);
>> +#endif
>> +	assert(disassemble);
>> +
>> +	fflush(s);
> 
> what's the reason for those fflush calls?

fflush() updates buf_size for the stream. This one before the 
loop make sure we read proper buf_size (prev_buf_size = bud_size)
in the first iteration. Then, the fflush() in each iteration 
makes sure the next iteration reads proper prev_buf_size. 

Thanks,
Song


> 
> thanks,
> jirka
> 
>> +	do {
>> +		const struct bpf_line_info *linfo = NULL;
>> +		struct disasm_line *dl;
>> +		size_t prev_buf_size;
>> +		const char *srcline;
>> +		u64 addr;
>> +
>> +		addr = pc + ((u64 *)(info_linear->info.jited_ksyms))[sub_id];
>> +		count = disassemble(pc, &info);
>> +
>> +		if (prog_linfo)
>> +			linfo = bpf_prog_linfo__lfind_addr_func(prog_linfo,
>> +								addr, sub_id,
>> +								nr_skip);
>> +
>> +		if (linfo && btf) {
>> +			srcline = btf__name_by_offset(btf, linfo->line_off);
>> +			nr_skip++;
>> +		} else
>> +			srcline = NULL;
>> +
>> +		fprintf(s, "\n");
>> +		prev_buf_size = buf_size;
>> +		fflush(s);
> 
> SNIP