Code compiled with profiling flag does not generate gmon.out
I compiled a code with gcc using the profiling flag (-pg), but when I run the program no gmon.out is generated.
I compiled a test code -- actually, the one from this question -- to see if the compilation flag & gprof were working and, yes, it worked.
To compile the code (named xrttimetag) the following line was used (here below I used -I(...) and -L(...) to hide a huge list of paths to other scientific libraries):
gcc -c -o ./xrttimetag.o -Wall --pedantic -Wno-comment -Wno-long-long -pg -fPIC -I(...) -DPACKAGE_NAME="" -DPACKAGE_TARNAME="" -DPACKAGE_VERSION="" -DPACKAGE_STRING="" -DPACKAGE_BUGREPORT="" -DPACKAGE_URL="" -Dg77Fortran=1 -DgFortran=1 -DHAVE_CONNECT=1 -DHAVE_ACCEPT=1 -DSTDC_HEADERS=1 -DHAVE_SYS_TYPES_H=1 -DHAVE_SYS_STAT_H=1 -DHAVE_STDLIB_H=1 -DHAVE_STRING_H=1 -DHAVE_MEMORY_H=1 -DHAVE_STRINGS_H=1 -DHAVE_INTTYPES_H=1 -DHAVE_STDINT_H=1 -DHAVE_UNISTD_H=1 -DHAVE_LIBM=1 -DHAVE_LIBDL=1 -DHAVE_LIBNCURSES=1 -DSIZEOF_LONG=8 xrttimetag.c
gcc -o xrttimetag xrttimetag.o -L(...) -lswxrt -latFunctions3.3 -lcoordfits -lcoord -lephemeris -lhdinit_2.7 -lhdutils_2.7 -lape_2.8 -lcfitsio_3.37 -lreadline -lhdio_2.7 -lncurses -ldl -lm -L/usr/lib64/gcc/x86_64-suse-linux/4.6 -L/usr/lib64/gcc/x86_64-suse-linux/4.6/../../../../lib64 -L/lib/../lib64 -L/usr/lib/../lib64 -L/usr/lib64/gcc/x86_64-suse-linux/4.6/../../../../x86_64-suse-linux/lib -L/usr/lib64/gcc/x86_64-suse-linux/4.6/../../.. -L/usr/lib64/gcc/x86_64-suse-linux/4.6 -L/usr/lib64/gcc/x86_64-suse-linux/4.6/../../../../lib64 -L/lib/../lib64 -L/usr/lib/../lib64 -L/usr/lib64/gcc/x86_64-suse-linux/4.6/../../../../x86_64-suse-linux/lib -L/usr/lib64/gcc/x86_64-suse-linux/4.6/../../.. -lgfortran -lm -lgcc_s -lgcc -lquadmath -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc
I looked for symbols related to gmon on the generated binary and they look a bit strange for me since they are undefined :
readelf -s `which xrttimetag` | egrep "gmon|mcount"
21: 0000000000000000 0 NOTYPE WEAK DEFAULT UND __gmon_start__
74: 0000000000000000 0 FUNC GLOBAL DEFAULT UND mcount@GLIBC_2.2.5 (2)
41: 000000000040267c 0 FUNC LOCAL DEFAULT 15 call_gmon_start
96: 0000000000000000 0 NOTYPE WEAK DEFAULT UND __gmon_start__
166: 0000000000000000 0 FUNC GLOBAL DEFAULT UND mcount@@GLIBC_2.2.5
On the other hand, the test code, I compiled with:
g++ -pg test.cpp
And the search for "gmon|mcount" symbols give me:
readelf -s test | egrep "gmon|mcount"
6: 0000000000000000 0 FUNC GLOBAL DEFAULT UND mcount@GLIBC_2.2.5 (3)
11: 0000000000400850 63 FUNC GLOBAL DEFAULT 15 __gmon_start__
40: 0000000000000000 0 FILE LOCAL DEFAULT ABS gmon-start.c
43: 0000000000400890 0 FUNC LOCAL DEFAULT 15 call_gmon_start
73: 0000000000400850 63 FUNC GLOBAL DEFAULT 15 __gmon_start__
91: 0000000000000000 0 FUNC GLOBAL DEFAULT UND mcount@@GLIBC_2.2.5
We can that the "gmon" symbols are well defined for the _ test_ code and not for the _ xrttimetag_, but I don't really understand why. What am I missing?
Thanks.
PS: I saw the question gmon.out is not written after compiling with gcc -pg -g , and this one is not a duplication, unless I had completely misunderstood that one.
Answer
You are not passing -pg when generating executable.
i.e.
gcc -o xrttimetag xrttimetag.o ....
You should pass -pg option here too. I can re-produce the problem (i.e. symbols are undefined for gmon* calls) if I use -pg when compiling but not when linking.
From the gcc documentation:
-pg
Generate extra code to write profile information suitable for the analysis program gprof. You must use this option when compiling the source files you want data about, and you must also use it when linking.