[Bug macros/27754] Excessive CPU load and memory usage with -g3 debug info

["simark at simark dot ca" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=27754

Simon Marchi <simark at simark dot ca> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |simark at simark dot ca

--- Comment #13 from Simon Marchi <simark at simark dot ca> ---
I am encountering something similar, although I don't use LTO.

My symptom is that when I do "thread apply all bt", there's a noticeable pause
of 2-3 seconds between each thread.  I added a bit of logging, that time is
spent expanding a single CU.  I profiled, and all that time is spent in
dwarf_decode_macros.

I'll attach a binary (lt-lttng-sessiond).

I am experimenting with:

$ ./gdb --data-directory=data-directory -nx
/home/simark/build/lttng-tools-noasan/src/bin/lttng-sessiond/.libs/lt-lttng-sessiond
-ex "maint expand register.c" -batch

Which expands the CU at 0x6a1c9.  That reads the macros at 0x2919d in
.debug_macro.  Here are the first few lines:

 DW_MACRO_import - offset : 0x0
 DW_MACRO_start_file - lineno: 0 filenum: 9 filename:
/home/simark/src/lttng-tools/src/bin/lttng-sessiond/register.c
 DW_MACRO_start_file - lineno: 0 filenum: 41 filename:
/usr/include/stdc-predef.h
 DW_MACRO_import - offset : 0x0
 DW_MACRO_end_file
 DW_MACRO_start_file - lineno: 0 filenum: 42 filename:
../../../include/config.h
 DW_MACRO_import - offset : 0x0
 DW_MACRO_end_file
 DW_MACRO_start_file - lineno: 10 filenum: 10 filename:
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/stddef.h
 DW_MACRO_import - offset : 0x0
 DW_MACRO_end_file
 DW_MACRO_start_file - lineno: 11 filenum: 43 filename: /usr/include/stdlib.h
 DW_MACRO_define_strp - lineno : 24 macro :
__GLIBC_INTERNAL_STARTING_HEADER_IMPLEMENTATION 
 DW_MACRO_start_file - lineno: 25 filenum: 44 filename:
/usr/include/bits/libc-header-start.h
 DW_MACRO_undef_strp - lineno : 31 macro :
__GLIBC_INTERNAL_STARTING_HEADER_IMPLEMENTATION
 DW_MACRO_start_file - lineno: 33 filenum: 45 filename: /usr/include/features.h
 DW_MACRO_import - offset : 0x0
 DW_MACRO_start_file - lineno: 473 filenum: 46 filename:
/usr/include/sys/cdefs.h
 DW_MACRO_import - offset : 0x0
 DW_MACRO_start_file - lineno: 462 filenum: 47 filename:
/usr/include/bits/wordsize.h
 DW_MACRO_import - offset : 0x0
 DW_MACRO_end_file
 DW_MACRO_start_file - lineno: 463 filenum: 48 filename:
/usr/include/bits/long-double.h
 ...

The imports at offset 0 look wrong.  First, there are a ton of them, one at
pretty much every included file.  But also because the macro informations at
offset 0 in .debug_macro are those of a totally unrelated CU.

When I check the relocations in the corresponding .o, I do see:

Relocation section '.rela.debug_macro' at offset 0x25cb0 contains 412 entries:
    Offset             Info             Type               Symbol's Value 
Symbol's Name + Addend
0000000000000003  0000002b0000000a R_X86_64_32            0000000000000000
.debug_line + 0
0000000000000008  0000002d0000000a R_X86_64_32            0000000000000000
.debug_macro + 0
0000000000000013  0000002e0000000a R_X86_64_32            0000000000000000
.debug_macro + 0
000000000000001c  0000002f0000000a R_X86_64_32            0000000000000000
.debug_macro + 0
0000000000000025  000000300000000a R_X86_64_32            0000000000000000
.debug_macro + 0


So the relocations are really asking for ".debug_macro + 0".

-- 
You are receiving this mail because:
You are on the CC list for the bug.