掌機 - Miyoo Mini Plus - 分析Perf Segmentation fault問題

問題如下：

# export LD_LIBRARY_PATH=lib
# ./perf record -p 1054
    Segmentation fault

分析如下：

# gdb ./perf record -p 1054

(gdb) r
    Starting program: /mnt/SDCARD/perf/perf record -p 1054
    warning: Unable to find libthread_db matching inferior's thread library, thread debugging will not be available.

    Program received signal SIGSEGV, Segmentation fault.
    0x00492ff0 in snprintf (__fmt=0x5975ec "%s%s", __n=4096, __s=0x1cacec0 "")
        at /opt/mmiyoo/arm-buildroot-linux-gnueabihf/sysroot/usr/include/bits/stdio2.h:67
    67      /opt/mmiyoo/arm-buildroot-linux-gnueabihf/sysroot/usr/include/bits/stdio2.h: No such file or directory.

(gdb) bt
    #0  0x00492ff0 in snprintf (__fmt=0x5975ec "%s%s", __n=4096, __s=0x1cacec0 "")
        at /opt/mmiyoo/arm-buildroot-linux-gnueabihf/sysroot/usr/include/bits/stdio2.h:67
    #1  perf_event__synthesize_kernel_mmap (tool=0x5d7918 <record>, 
        process=0x41d460 <process_synthesized_event>, 
        machine=machine@entry=0x1ca4da0) at util/event.c:714
    #2  0x0041ded4 in record__synthesize (tail=tail@entry=false, 
        rec=0x5d7918 <record>) at builtin-record.c:792
    #3  0x0041ee6c in __cmd_record (rec=0x5d7918 <record>, argv=<optimized out>, 
        argc=0) at builtin-record.c:916
    #4  cmd_record (argc=0, argv=<optimized out>, prefix=<optimized out>)
        at builtin-record.c:1700
    #5  0x004859e0 in run_builtin (argv=0xbefffe08, argc=3, 
        p=0x5d89ec <commands+84>) at perf.c:357
    #6  handle_internal_command (argc=3, argv=0xbefffe08) at perf.c:419
    #7  0x0040f674 in run_argv (argv=0xbefffb68, argcp=0xbefffb6c) at perf.c:609
    #8  main (argc=<optimized out>, argv=<optimized out>) at perf.c:609

Crash Point

int perf_event__synthesize_kernel_mmap(struct perf_tool *tool,
                       perf_event__handler_t process,
                       struct machine *machine)
{
    ...
    size = snprintf(event->mmap.filename, sizeof(event->mmap.filename),
            "%s%s", mmap_name, kmap->ref_reloc_sym->name) + 1;

這個Crash的點真的蠻奇特，找了一下，還是找不出問題，使用如下Workaround就可以解決

int perf_event__synthesize_kernel_mmap(struct perf_tool *tool,
                       perf_event__handler_t process,
                       struct machine *machine)
{
    return 0;
}

雖然缺少一些Kernel資訊，不過，用來找出User Application的效能瓶頸，這樣的解決還是可以接受的

# export LD_LIBRARY_PATH=lib
# ./perf record -p 1054
# ./perf report