15.1.1 List of Filename Extensions and Languages

If a source file name ends in one of the following extensions, then GDB infers that its language is the one indicated.

.ada

.ads

.adb

.a

Ada source file.

.c

C source file

.C

.cc

.cp

.cpp

.cxx

.c++

C++ source file

.d

D source file

.m

Objective-C source file

.f

.F

Fortran source file

.mod

Modula-2 source file

.s

.S

Assembler source file. This actually behaves almost like C, but GDB does not skip over function prologues when stepping.

In addition, you may set the language associated with a filename extension. See Displaying the Language.