Patch "perf probe: Fix probe definition for inlined functions" has been added to the 4.11-stable tree

This is a note to let you know that I've just added the patch titled

perf probe: Fix probe definition for inlined functions

to the 4.11-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
perf-probe-fix-probe-definition-for-inlined-functions.patch
and it can be found in the queue-4.11 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: =?UTF-8?q?Bj=C3=B6rn=20T=C3=B6pel?= <[email protected]>
Date: Wed, 21 Jun 2017 18:41:34 +0200
Subject: perf probe: Fix probe definition for inlined functions
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
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From: Björn Töpel <[email protected]>

commit 7598f8bc1383ffd77686cb4e92e749bef3c75937 upstream.

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/

---
 tools/perf/util/probe-event.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -615,7 +615,7 @@ static int post_process_probe_trace_poin
 					   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)

Patches currently in stable-queue which might be from [email protected] are

queue-4.11/perf-probe-fix-probe-definition-for-inlined-functions.patch