Detect if an ELF binary was built with gprof instrumentation?

Question

Is it possible to check if given program was compiled with GNU gprof instrumentation, i.e. with '-pg' flag passed to both compiler and linker, without running it to check if it would generate a gmon.out file?

Answer 1

You could check for references to function mcount (or possibly _mcount or __mcount according to Implementation of Profiling). This function is necessary for profiling to work, and should be absent for non-profiled binaries.

Something like:

$ readelf -s someprog | egrep "\s(_+)?mcount\b" && echo "Profiling is on for someprog"

The above works on a quick test here.

Answer 2

The regular expression in the answer above doesn't always work...but the general idea of grepping for "mcount" in the output of 'readelf -s [binary]' is correct, I think

Answer 3

Adding more to the answers:

1. To check for instrumentation, grep for mcount/gmon:

   $  readelf -s <binary> | egrep "gmon|mcount"    
   20: 0000000000401160    63 FUNC    GLOBAL DEFAULT   12 __gmon_start__    
   28: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND mcount@GLIBC_2.2.5 (2)    
   36: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS gmon-start.c    
   39: 00000000004011a0     0 FUNC    LOCAL  DEFAULT   12 call_gmon_start    
   100: 0000000000401160    63 FUNC    GLOBAL DEFAULT   12 __gmon_start__    
   114: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND mcount@@GLIBC_2.2.5    
   

2. One needs to compile as well as link with -pg flags, otherwise gmon.out will not be generated. stackoverflow link.

3. I found that the binary on which I was running gprof didn't generate any gmon.out file, despite compiling/linking with -pg flag. The reason being - I was killing my application, it wasn't a clean exit. gprof generates output only when the program exits normally. stackoverflow link