How to find out which compiler was used: g77 or gfortran

Question

Hi,

I'm compiling library for a private project, which depends on a number of libraries. Specifically one of the dependencies is compiled with Fortran. On some instances, I've seen the dependency compiled with g77, on others I've seen it compiled with gfortran. My project then is ./configure'd to link with either -lg2c or -lgfortran, but so far I've been doing it by hand.

If it is possible, how can I find out, from looking into the dependent library (via e.g. nm or some other utility?), whether the used compiler was g77 (and then I'll use -lg2c in my link options) or gfortran (and then I'll use -lgfortran)?

Thanks in advance!

Answer 1

You might be able to figure it out by using nm, and seeing if the compiled code uses functions from one or the other, but that's quite a hack. You may be able to figure it out based on which library is available (if there's no libg2c available, then it wasn't g77, for example), but then you still have some ambiguity if both are available. If you can build the dependency yourself, then you can use have one part of your build process tell another part somehow (variable, file, etc.) which one you used.

Answer 2

nm filename | fgrep ' __g77'

will give results if g77 was used, meanwhile

nm filename | fgrep '@@GFORTRAN'

will give results if gfortran is used.

Answer 3

You need to grep for something, in the output of nm filename, that indicates whether g77 or gfortran was used. In most cases, if the library does at least input-output in one place, it will call libg2c or libgfortran and you will notice a symbol with g77 in it, or gfortran. So, your best bet is to use grep:

nm filename | grep _g77_
nm filename | grep _gfortran_

Two notes:

1. Grepping for @@GFORTRAN as geocar suggested is not reliable: it will only work on platforms where library-versioning is supported, which includes e.g. linux but not Windows or Mac OS.
2. It is still possible that some compiled code calls absolutely no support library function (if all it does is simple arithmetic and has not input-output, e.g.). In that case, unless it's compiled with debugging options, it's impossible to tell which compiler output it.