• Arnaldo Carvalho de Melo's avatar
    perf tools: Handle relocatable kernels · 56b03f3c
    Arnaldo Carvalho de Melo authored
    DSOs don't have this problem because the kernel emits a
    PERF_MMAP for each new executable mapping it performs on
    monitored threads.
    
    To fix the kernel case we simulate the same behaviour, by having
    'perf record' to synthesize a PERF_MMAP for the kernel, encoded
    like this:
    
    [root@doppio ~]# perf record -a -f sleep 1
    [ perf record: Woken up 1 times to write data ]
    [ perf record: Captured and wrote 0.344 MB perf.data (~15038 samples) ]
    [root@doppio ~]# perf report -D | head -10
    
    0xd0 [0x40]: event: 1
    .
    . ... raw event: size 64 bytes
    .  0000:  01 00 00 00 00 00 40 00 00 00 00 00 00 00 00 00 ......@........
    .  0010:  00 00 00 81 ff ff ff ff 00 00 00 00 00 00 00 00 ...............
    .  0020:  00 00 00 00 00 00 00 00 5b 6b 65 72 6e 65 6c 2e ........  [kernel
    .  0030:  6b 61 6c 6c 73 79 6d 73 2e 5f 74 65 78 74 5d 00  kallsyms._text]
    .  0xd0
    [0x40]: PERF_RECORD_MMAP 0/0: [0xffffffff81000000((nil)) @ (nil)]: [kernel.kallsyms._text]
    
    I.e. we identify such event as having:
    
     .pid      = 0
     .filename = [kernel.kallsyms.REFNAME]
     .start    = REFNAME addr in /proc/kallsyms at 'perf record' time
    
    and use now a hardcoded value of '.text' for REFNAME.
    
    Then, later, in 'perf report', if there are any kernel hits and
    thus we need to resolve kernel symbols, we search for REFNAME
    and if its address changed, relocation happened and we thus must
    change the kernel mapping routines to one that uses .pgoff as
    the relocation to apply.
    
    This way we use the same mechanism used for the other DSOs and
    don't have to do a two pass in all the kernel symbols.
    Reported-by: default avatarXiao Guangrong <xiaoguangrong@cn.fujitsu.com>
    Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
    Cc: Frédéric Weisbecker <fweisbec@gmail.com>
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Cc: Mike Galbraith <efault@gmx.de>
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Paul Mackerras <paulus@samba.org>
    Cc: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
    LKML-Reference: <1262717431-1246-1-git-send-email-acme@infradead.org>
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    56b03f3c
session.h 1.72 KB