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    perf probe: Fix probe definition for inlined functions · 7598f8bc
    Björn Töpel 提交于
    In commit 613f050d ("perf probe: Fix to probe on gcc generated
    functions in modules"), the offset from symbol is, incorrectly, added
    to the trace point address. This leads to incorrect probe trace points
    for inlined functions and when using relative line number on symbols.
    
    Prior this patch:
      $ perf probe -m nf_nat -D in_range
      p:probe/in_range nf_nat:in_range.isra.9+0
      $ perf probe -m i40e -D i40e_clean_rx_irq
      p:probe/i40e_clean_rx_irq i40e:i40e_napi_poll+2212
      $ perf probe -m i40e -D i40e_clean_rx_irq:16
      p:probe/i40e_clean_rx_irq i40e:i40e_lan_xmit_frame+626
    
    After:
      $ perf probe -m nf_nat -D in_range
      p:probe/in_range nf_nat:in_range.isra.9+0
      $ perf probe -m i40e -D i40e_clean_rx_irq
      p:probe/i40e_clean_rx_irq i40e:i40e_napi_poll+1106
      $ perf probe -m i40e -D i40e_clean_rx_irq:16
      p:probe/i40e_clean_rx_irq i40e:i40e_napi_poll+2665
    
    Committer testing:
    
    Using 'pfunct', a tool found in the 'dwarves' package [1], one can ask what are
    the functions that while not being explicitely marked as inline, were inlined
    by the compiler:
    
      # pfunct --cc_inlined /lib/modules/4.12.0-rc4+/kernel/drivers/net/ethernet/intel/e1000e/e1000e.ko | head
      __ew32
      e1000_regdump
      e1000e_dump_ps_pages
      e1000_desc_unused
      e1000e_systim_to_hwtstamp
      e1000e_rx_hwtstamp
      e1000e_update_rdt_wa
      e1000e_update_tdt_wa
      e1000_put_txbuf
      e1000_consume_page
    
    Then ask 'perf probe' to produce the kprobe_tracer probe definitions for two of
    them:
    
      # perf probe -m e1000e -D e1000e_rx_hwtstamp
      p:probe/e1000e_rx_hwtstamp e1000e:e1000_receive_skb+74
    
      # perf probe -m e1000e -D e1000_consume_page
      p:probe/e1000_consume_page e1000e:e1000_clean_jumbo_rx_irq+876
      p:probe/e1000_consume_page_1 e1000e:e1000_clean_jumbo_rx_irq+1506
      p:probe/e1000_consume_page_2 e1000e:e1000_clean_rx_irq_ps+1074
    
    Now lets concentrate on the 'e1000_consume_page' one, that was inlined twice in
    e1000_clean_jumbo_rx_irq(), lets see what readelf says about the DWARF tags for
    that function:
    
      $ readelf -wi /lib/modules/4.12.0-rc4+/kernel/drivers/net/ethernet/intel/e1000e/e1000e.ko
      <SNIP>
      <1><13e27b>: Abbrev Number: 121 (DW_TAG_subprogram)
        <13e27c>   DW_AT_name        : (indirect string, offset: 0xa8945): e1000_clean_jumbo_rx_irq
        <13e287>   DW_AT_low_pc      : 0x17a30
      <3><13e6ef>: Abbrev Number: 119 (DW_TAG_inlined_subroutine)
        <13e6f0>   DW_AT_abstract_origin: <0x13ed2c>
        <13e6f4>   DW_AT_low_pc      : 0x17be6
      <SNIP>
      <1><13ed2c>: Abbrev Number: 142 (DW_TAG_subprogram)
         <13ed2e>   DW_AT_name        : (indirect string, offset: 0xa54c3): e1000_consume_page
    
    So, the first time in e1000_clean_jumbo_rx_irq() where e1000_consume_page() is
    inlined is at PC 0x17be6, which subtracted from e1000_clean_jumbo_rx_irq()'s
    address, gives us the offset we should use in the probe definition:
    
      0x17be6 - 0x17a30 = 438
    
    but above we have 876, which is twice as much.
    
    Lets see the second inline expansion of e1000_consume_page() in
    e1000_clean_jumbo_rx_irq():
    
      <3><13e86e>: Abbrev Number: 119 (DW_TAG_inlined_subroutine)
        <13e86f>   DW_AT_abstract_origin: <0x13ed2c>
        <13e873>   DW_AT_low_pc      : 0x17d21
    
      0x17d21 - 0x17a30 = 753
    
    So we where adding it at twice the offset from the containing function as we
    should.
    
    And then after this patch:
    
      # perf probe -m e1000e -D e1000e_rx_hwtstamp
      p:probe/e1000e_rx_hwtstamp e1000e:e1000_receive_skb+37
    
      # perf probe -m e1000e -D e1000_consume_page
      p:probe/e1000_consume_page e1000e:e1000_clean_jumbo_rx_irq+438
      p:probe/e1000_consume_page_1 e1000e:e1000_clean_jumbo_rx_irq+753
      p:probe/e1000_consume_page_2 e1000e:e1000_clean_jumbo_rx_irq+1353
      #
    
    Which matches the two first expansions and shows that because we were
    doubling the offset it would spill over the next function:
    
      readelf -sw /lib/modules/4.12.0-rc4+/kernel/drivers/net/ethernet/intel/e1000e/e1000e.ko
       673: 0000000000017a30  1626 FUNC    LOCAL  DEFAULT    2 e1000_clean_jumbo_rx_irq
       674: 0000000000018090  2013 FUNC    LOCAL  DEFAULT    2 e1000_clean_rx_irq_ps
    
    This is the 3rd inline expansion of e1000_consume_page() in
    e1000_clean_jumbo_rx_irq():
    
       <3><13ec77>: Abbrev Number: 119 (DW_TAG_inlined_subroutine)
        <13ec78>   DW_AT_abstract_origin: <0x13ed2c>
        <13ec7c>   DW_AT_low_pc      : 0x17f79
    
      0x17f79 - 0x17a30 = 1353
    
     So:
    
       0x17a30 + 2 * 1353 = 0x184c2
    
      And:
    
       0x184c2 - 0x18090 = 1074
    
    Which explains the bogus third expansion for e1000_consume_page() to end up at:
    
       p:probe/e1000_consume_page_2 e1000e:e1000_clean_rx_irq_ps+1074
    
    All fixed now :-)
    
    [1] https://git.kernel.org/pub/scm/devel/pahole/pahole.git/Signed-off-by: NBjörn Töpel <bjorn.topel@intel.com>
    Tested-by: NArnaldo Carvalho de Melo <acme@redhat.com>
    Acked-by: NMagnus Karlsson <magnus.karlsson@intel.com>
    Acked-by: NMasami Hiramatsu <mhiramat@kernel.org>
    Cc: stable@vger.kernel.org
    Fixes: 613f050d ("perf probe: Fix to probe on gcc generated functions in modules")
    Link: http://lkml.kernel.org/r/20170621164134.5701-1-bjorn.topel@gmail.comSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
    7598f8bc
probe-event.c 78.9 KB