| Summary: | [test] gmon/tst-gmon-gprof* may have a f3 line when built with ld.lld | ||
|---|---|---|---|
| Product: | glibc | Reporter: | Fangrui Song <i> |
| Component: | libc | Assignee: | Not yet assigned to anyone <unassigned> |
| Status: | RESOLVED FIXED | ||
| Severity: | normal | CC: | drepper.fsp, hjl.tools |
| Priority: | P2 | ||
| Version: | 2.34 | ||
| Target Milestone: | 2.35 | ||
| Host: | Target: | ||
| Build: | Last reconfirmed: | 2021-07-29 00:00:00 | |
|
Description
Fangrui Song
2021-07-28 21:10:32 UTC
On ld.bfd generated gmon/tst-gmon, gprof shows
ndex % time self children called name
0.00 0.00 1000/2000 f2 [2]
0.00 0.00 1000/2000 f3 [7]
[1] 0.0 0.00 0.00 2000 f1 [1]
-----------------------------------------------
0.00 0.00 1000/1000 f3 [7]
[2] 0.0 0.00 0.00 1000 f2 [2]
0.00 0.00 1000/2000 f1 [1]
-----------------------------------------------
...
Index by function name
[1] f1 [2] f2
Why do you think the output is incorrect?
lld linked gmon/tst-gmon has f3.
% cd ~/Dev/glibc/out/lld
% ./testrun.sh gmon/tst-gmon
% gprof gmon/tst-gmon
...
Call graph (explanation follows)
granularity: each sample hit covers 4 byte(s) no time propagated
index % time self children called name
0.00 0.00 1000/2000 f2 [2]
0.00 0.00 1000/2000 f3 [3]
[1] 0.0 0.00 0.00 2000 f1 [1]
-----------------------------------------------
0.00 0.00 1000/1000 f3 [3]
[2] 0.0 0.00 0.00 1000 f2 [2]
0.00 0.00 1000/2000 f1 [1]
-----------------------------------------------
0.00 0.00 1/1 main [9]
[3] 0.0 0.00 0.00 1 f3 [3]
0.00 0.00 1000/1000 f2 [2]
0.00 0.00 1000/2000 f1 [1]
-----------------------------------------------
...
Index by function name
[1] f1 [2] f2 [3] f3
ld.bfd generates: 0000000000401000 T _init 0000000000401090 T main 00000000004010b0 T _start 00000000004010e0 T __gmon_start__ 0000000000401130 t deregister_tm_clones 0000000000401160 t register_tm_clones 00000000004011a0 t __do_global_dtors_aux 00000000004011d0 t frame_dummy 0000000000401250 T atexit 0000000000401264 T _fini 0000000000401271 T etext ld.lld generates: 0000000000201ba0 T _start 0000000000201bd0 T __gmon_start__ 0000000000201c20 t deregister_tm_clones 0000000000201c50 t register_tm_clones 0000000000201c90 t __do_global_dtors_aux 0000000000201cc0 t frame_dummy 0000000000201d40 T main 0000000000201d60 t atexit 0000000000201d74 t _init 0000000000201d90 t _fini 0000000000201e10 T etext glibc assumes that _start is the lowest address for which we need o keep profiling records. The newer GCC places main in .text.startup section. Since _start is in .text section, ld.bfd places main below _start. Put _start in .text.startup section makes f3 to show up with ld.bfd. A patch is posted at https://sourceware.org/pipermail/libc-alpha/2021-July/129685.html Fixed for glibc 2.35 by commit 84a7eb1f87c1d01b58ad887a0ab5d87abbc1c772 Author: H.J. Lu <hjl.tools@gmail.com> Date: Fri Jul 30 19:07:30 2021 -0700 Use __executable_start as the lowest address for profiling [BZ #28153] Glibc assumes that ENTRY_POINT is the lowest address for which we need to keep profiling records and BFD linker uses a linker script to place the input sections. Starting from GCC 4.6, the main function is placed in .text.startup section and starting from binutils 2.22, BFD linker with commit add44f8d5c5c05e08b11e033127a744d61c26aee Author: Alan Modra <amodra@gmail.com> Date: Thu Nov 25 03:03:02 2010 +0000 * scripttempl/elf.sc: Group .text.exit, text.startup and .text.hot sections. places .text.startup section before .text section, which leave the main function out of profiling records. Starting from binutils 2.15, linker provides __executable_start to mark the lowest address of the executable. Use __executable_start as the lowest address to keep the main function in profiling records. This fixes [BZ #28153]. Tested on Linux/x86-64, Linux/x32 and Linux/i686 as well as with build-many-glibcs.py. |