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

[Song Liu]

> On Mar 4, 2019, at 5:53 AM, Jiri Olsa <jo...@redhat.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