From: Björn Töpel bjorn.topel@intel.com
[ Upstream commit 7598f8bc1383ffd77686cb4e92e749bef3c75937 ]
In commit 613f050d68a8 ("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: 613f050d68a8 ("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 Signed-off-by: Sasha Levin sashal@kernel.org --- tools/perf/util/probe-event.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c index c93daccec755..a7452fd3b6ee 100644 --- a/tools/perf/util/probe-event.c +++ b/tools/perf/util/probe-event.c @@ -615,7 +615,7 @@ static int post_process_probe_trace_point(struct probe_trace_point *tp, struct map *map, unsigned long offs) { struct symbol *sym; - u64 addr = tp->address + tp->offset - offs; + u64 addr = tp->address - offs;
sym = map__find_symbol(map, addr); if (!sym)