In commit 613f050d68 ("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: Björn Töpel <bjorn.topel@intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: stable@vger.kernel.org
Fixes: 613f050d68 ("perf probe: Fix to probe on gcc generated functions in modules")
Link: http://lkml.kernel.org/r/20170621164134.5701-1-bjorn.topel@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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