Howto debug a (slow) linker on a debian system

Question

At my company we have a really annoying problem with our linker (ld 2.17). It links very very slow on a relatively fast system (Core Duo, 2GB Ram) and I don't really now how to fix this. It takes about five to ten minutes to compile a relatively big project (which takes about 5 seconds to link on my Gentoo system). Personally i think it is a huge productivity killer, at least for me. We tried to use a more recent version of ld (2.19) but without any success. I asked in #debian on #freenode, but this problem seems to be very unique. I did not find any information about similar problems on the net. It only happens when we build with debug symbols. I changed the gcc debug-information flags to -g, -g3, and -ggdb, but that did not help either. So my question is, how do you profile and debug a linker? I have never done anything like it, and I am unable to find any documentation about it. Basically any reasonable gprof gmon.out would be very helpful, as I could ask the binutils developers ab…

Accepted Answer

If you're observing the slowdown running `gcc` (as opposed to directly running the linker as `ld`), try compiling with

```
$ gcc -save-temps -v [... rest of your command line ...]
```

This will print out all the intermediary commands, such as the internal `collect2` and final `ld`, as well as ensure that the objects passed to those commands will remain on disk even after the command has completed.

Then you should be able to run the commands individually to find the worst stage, and then run it with different options or profiling.

For example,

```
$ echo 'int main() {}' > test.c
$ gcc -save-temps -v test.c
Using built-in specs.
Target: x86_64-pc-linux-gnu
Configured with: /var/tmp/paludis/sys-devel-gcc-4.3.3-r2/work/gcc-4.3.3/configure --prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/4.3.3 --includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/include --datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.3.3 --mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.3.3/man --infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.3.3/info --with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/include/g++-v4 --host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --disable-altivec --disable-fixed-point --enable-nls --without-included-gettext --with-system-zlib --disable-checking --disable-werror --enable-secureplt --enable-multilib --enable-libmudflap --disable-libssp --enable-libgomp --enable-cld --disable-libgcj --enable-objc-gc --enable-languages=c,c++,objc,obj-c++,treelang,fortran --enable-shared --enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu --with-bugurl=http://bugs.gentoo.org/ --with-pkgversion='Gentoo 4.3.3-r2 p1.1, pie-10.1.5'
Thread model: posix
gcc version 4.3.3 (Gentoo 4.3.3-r2 p1.1, pie-10.1.5)
COLLECT_GCC_OPTIONS='-save-temps' '-v' '-mtune=generic'
 /usr/libexec/gcc/x86_64-pc-linux-gnu/4.3.3/cc1 -E -quiet -v test.c -D_FORTIFY_SOURCE=2 -mtune=generic -fpch-preprocess -o test.i
ignoring nonexistent directory "/usr/local/include"
ignoring nonexistent directory "/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/../../../../x86_64-pc-linux-gnu/include"
#include "..." search starts here:
#include  search starts here:
 /usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/include
 /usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/include-fixed
 /usr/include
End of search list.
COLLECT_GCC_OPTIONS='-save-temps' '-v' '-mtune=generic'
 /usr/libexec/gcc/x86_64-pc-linux-gnu/4.3.3/cc1 -fpreprocessed test.i -quiet -dumpbase test.c -mtune=generic -auxbase test -version -o test.s
GNU C (Gentoo 4.3.3-r2 p1.1, pie-10.1.5) version 4.3.3 (x86_64-pc-linux-gnu)
        compiled by GNU C version 4.3.3, GMP version 4.2.4, MPFR version 2.4.1-p5.
warning: GMP header version 4.2.4 differs from library version 4.3.1.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 20f3dbffbfd03e5311a257ae1239cd71
COLLECT_GCC_OPTIONS='-save-temps' '-v' '-mtune=generic'
 /usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/../../../../x86_64-pc-linux-gnu/bin/as -V -Qy -o test.o test.s
GNU assembler version 2.19.1 (x86_64-pc-linux-gnu) using BFD version (GNU Binutils) 2.19.1
COMPILER_PATH=/usr/libexec/gcc/x86_64-pc-linux-gnu/4.3.3/:/usr/libexec/gcc/x86_64-pc-linux-gnu/4.3.3/:/usr/libexec/gcc/x86_64-pc-linux-gnu/:/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/:/usr/lib/gcc/x86_64-pc-linux-gnu/:/usr/libexec/gcc/x86_64-pc-linux-gnu/4.3.3/:/usr/libexec/gcc/x86_64-pc-linux-gnu/:/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/:/usr/lib/gcc/x86_64-pc-linux-gnu/:/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/../../../../x86_64-pc-linux-gnu/bin/
LIBRARY_PATH=/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/:/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/:/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/../../../../lib64/:/lib/../lib64/:/usr/lib/../lib64/:/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/../../../../x86_64-pc-linux-gnu/lib/:/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-save-temps' '-v' '-mtune=generic'
 /usr/libexec/gcc/x86_64-pc-linux-gnu/4.3.3/collect2 --eh-frame-hdr -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 /usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/../../../../lib64/crt1.o /usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/../../../../lib64/crti.o /usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/crtbegin.o -L/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3 -L/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3 -L/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/../../../../lib64 -L/lib/../lib64 -L/usr/lib/../lib64 -L/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/../../../../x86_64-pc-linux-gnu/lib -L/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/../../.. test.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/crtend.o /usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/../../../../lib64/crtn.o
$ ls
a.out  test.c  test.i  test.o  test.s
$ /usr/libexec/gcc/x86_64-pc-linux-gnu/4.3.3/collect2 --eh-frame-hdr -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 /usr/lib/gcc/x86_64-pc-linux-gnu/4.3.3/../../../../lib64/crt1.o /us…

Howto debug a (slow) linker on a debian system

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