excessive amount of startup time is spent in ld

[llvmbot]

Bugzilla Link	3847
Resolution	INVALID
Resolved on	Mar 20, 2009 10:57
Version	trunk
OS	Linux
Reporter	LLVM Bugzilla Contributor

Extended Description

Even with the recent work to use an export map, LLVM tools are still spending an unreasonable amount of time in the dynamic linker on Linux.

Over 2 million instructions just to print an error message:

ddunbar@frank:tmp$ valgrind --tool=callgrind ~/llvm/Release-Asserts/bin/llvm-ar
==31810== Callgrind, a call-graph generating cache profiler.
==31810== Copyright (C) 2002-2008, and GNU GPL'd, by Josef Weidendorfer et al.
==31810== Using LibVEX rev 1884, a library for dynamic binary translation.
==31810== Copyright (C) 2004-2008, and GNU GPL'd, by OpenWorks LLP.
==31810== Using valgrind-3.4.1-Debian, a dynamic binary instrumentation framework.
==31810== Copyright (C) 2000-2008, and GNU GPL'd, by Julian Seward et al.
==31810== For more details, rerun with: -v
==31810==
==31810== For interactive control, run 'callgrind_control -h'.
llvm-ar: Not enough positional command line arguments specified!
Must specify at least 2 positional arguments: See: /home/ddunbar/llvm/Release-Asserts/bin/llvm-ar --help
==31810==
==31810== Events : Ir
==31810== Collected : 2178896
==31810==
==31810== I refs: 2,178,896

Here is the tools link line:

g++ -I/home/ddunbar/llvm.trunk/include -I/home/ddunbar/llvm.trunk/tools/llvm-ar -DNDEBUG -D_GNU_SOURCE -D__STDC_LIMIT_MACROS -D__STDC_CONSTANT_MACROS -O3 -fomit-frame-pointer -fPIC -Woverloaded-virtual -pedantic -Wall -W -Wwrite-strings -Wno-long-long -Wunused -Wno-unused-parameter -O3 -Wl,-R -Wl,/home/ddunbar/llvm.trunk/Release-Asserts/bin -Wl,-export-dynamic -L/home/ddunbar/llvm.trunk/Release-Asserts/lib -L/home/ddunbar/llvm.trunk/Release-Asserts/lib -Wl,--version-script=/home/ddunbar/llvm.trunk/autoconf/ExportMap.map -o /home/ddunbar/llvm.trunk/Release-Asserts/bin/llvm-ar /home/ddunbar/llvm.trunk/tools/llvm-ar/Release-Asserts/llvm-ar.o
-lLLVMArchive -lLLVMBitReader -lLLVMCore -lLLVMSupport -lLLVMSystem -lpthread -ldl -lm -lelf

and nm shows 2644 external symbols:

ddunbar@frank:tmp$ nm --extern-only ~/llvm/Release-Asserts/bin/llvm-ar | wc -l
2644

[llvmbot]

Ok, apparently this is just general C++ lameness on Linux. Gross.

The mind boggles:

ddunbar@frank:tmp$ cat t.c
int main() { return 0; }
ddunbar@frank:tmp$ gcc t.c && valgrind --tool=callgrind ./a.out
==22836== Callgrind, a call-graph generating cache profiler.
==22836== Copyright (C) 2002-2008, and GNU GPL'd, by Josef Weidendorfer et al.
==22836== Using LibVEX rev 1884, a library for dynamic binary translation.
==22836== Copyright (C) 2004-2008, and GNU GPL'd, by OpenWorks LLP.
==22836== Using valgrind-3.4.1-Debian, a dynamic binary instrumentation framework.
==22836== Copyright (C) 2000-2008, and GNU GPL'd, by Julian Seward et al.
==22836== For more details, rerun with: -v
==22836==
==22836== For interactive control, run 'callgrind_control -h'.
==22836==
==22836== Events : Ir
==22836== Collected : 125977
==22836==
==22836== I refs: 125,977

ddunbar@frank:tmp$ g++ t.c && valgrind --tool=callgrind ./a.out
==22845== Callgrind, a call-graph generating cache profiler.
==22845== Copyright (C) 2002-2008, and GNU GPL'd, by Josef Weidendorfer et al.
==22845== Using LibVEX rev 1884, a library for dynamic binary translation.
==22845== Copyright (C) 2004-2008, and GNU GPL'd, by OpenWorks LLP.
==22845== Using valgrind-3.4.1-Debian, a dynamic binary instrumentation framework.
==22845== Copyright (C) 2000-2008, and GNU GPL'd, by Julian Seward et al.
==22845== For more details, rerun with: -v
==22845==
==22845== For interactive control, run 'callgrind_control -h'.
==22845==
==22845== Events : Ir
==22845== Collected : 1369136
==22845==
==22845== I refs: 1,369,136

[llvmbot]

If you use the new gold linker then linking the LLVM
libraries turns from being a horrible moment during
which your computer is dieing of a heart attack into
something so quick and easy you don't even notice.

[llvmbot]

Good to know; this bug was about startup time though. I get to pay that every time I run any LLVM tool. :)