1632972 - shared-libraries-linux.cc does not emit a SharedLibrary for the firefox binary, causing missing symbols for mozjemalloc and other functions

Status: RESOLVED FIXED

(Core :: Gecko Profiler, defect, P2)

Description

[Emilio Cobos Álvarez (:emilio)]

STR:

• Profile something. I have a profile that shows this issue in bug 1632469 comment 8. That's from a local build but it happens on official builds too.

• Try to look on any of the jemalloc functions, so anything that goes under replace_malloc|free|moz_arena_malloc|....

ER:

• See the symbols for the functions.

AR:

• Only a bunch of addresses.

Comment 1

[Markus Stange [:mstange]]

This indicates that shared-libraries-linux.cc is not able to find the address range for the library that contains these functions.

Comment 2

[Emilio Cobos Álvarez (:emilio)]

(In reply to Markus Stange [:mstange] from comment #1)

This indicates that shared-libraries-linux.cc is not able to find the address range for the library that contains these functions.

I don't get it, those are in libxul aren't they?

Comment 3

[Markus Stange [:mstange]]

In the profile, libxul covers the address range 0x7fb3723b3000 - 0x7fb379fa5390, but the unsymbolicated addresses such as 0x55629110f8ce are before that range. Then maybe we sample incorrect addresses?

Comment 4

[Mike Hommey [:glandium]]

The allocator symbols are in firefox on linux. Depending what shared-libraries-linux.cc does, it might not see them.

Comment 5

[Markus Stange [:mstange]]

Thanks!

Comment 6

[Gerald Squelart (he/him) (not at Mozilla since 2022-09-15)]

Confirming it's only on Linux, as I could see the alloc functions on Mac and Windows.

Comment 7

[Emilio Cobos Álvarez (:emilio)]

I'd like to poke at this, if I don't find the culprit I'll unassign myself.

Comment 8

[Emilio Cobos Álvarez (:emilio)]

Attachment: Bug 1632972 - Fix logic to detect the main executable. r=mstange

This is how my mapfile looks like:

5587df936000-5587df96b000 r--p 00000000 fd:02 21584889 /home/emilio/src/moz/gecko/obj-debug/dist/bin/firefox
5587df96b000-5587df9ec000 r-xp 00035000 fd:02 21584889 /home/emilio/src/moz/gecko/obj-debug/dist/bin/firefox
5587df9ec000-5587df9ed000 r--p 000b6000 fd:02 21584889 /home/emilio/src/moz/gecko/obj-debug/dist/bin/firefox
5587df9ed000-5587df9ee000 rw-p 000b7000 fd:02 21584889 /home/emilio/src/moz/gecko/obj-debug/dist/bin/firefox

Note how the executable bit, which is the only one we look at, and which
is where we get exeExeAddr from (0x5587df96b000 in this case) is in the
middle of the executable, but the library will span all four ranges.

Check for whether the library contains the start address of the
executable region instead of whether it starts with it.

Comment 9

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/47afa4ab35f8
Fix logic to detect the main executable. r=mstange

Comment 10

[Natalia Csoregi [:nataliaCs]]

https://hg.mozilla.org/mozilla-central/rev/47afa4ab35f8