gcc 4.3.3 compiler options enabled by default

Question

I have moved from gcc version 4.0.3 to 4.3.3 and realized that -mfpmath was set to sse by default in gcc 4.3.3. This actually caused errors in my application. In 4.0.3 the -mfpmath was 387.

I want to know how I can get all the default options enabled by gcc for a given version. How can I dump set of all options used by gcc while compiling. This enables me to compare version 4.0.3 vs 4.3.3.

In general it will be great if I can know a comprehensive list of things need to be checked before going for a version change in gcc .(As this has effect on performance and functionality.)

Answer 1

gcc -Q -v

With just a basic tiny c or cpp file as an input file. Should give you a big list of all the options passed to gcc by default, one of those might be causing sse fp math to be enabled.

Answer 2

In addition to compiling a specific file -Q -v, which outputs the list of passed and enabled options, as well as a lots of other version, configuration, and timing information, you can also use gcc -Q --help=target to just list default target-specific compiler options:

$ gcc --version | head -1
gcc (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3
$ gcc -Q --help=target
The following options are target specific:
  -m128bit-long-double                  [disabled]
  -m32                                  [disabled]
  -m3dnow                               [disabled]
  -m3dnowa                              [disabled]
  -m64                                  [enabled]
  -m80387                               [enabled]
  -m8bit-idiv                           [disabled]
  -m96bit-long-double                   [enabled]
  -mabi=
  -mabm                                 [disabled]
  -maccumulate-outgoing-args            [disabled]
  -maes                                 [disabled]
  -malign-double                        [disabled]
  -malign-functions=
  -malign-jumps=
  -malign-loops=
  -malign-stringops                     [enabled]
  -mandroid                             [disabled]
  -march=                               x86-64
...

To also include a list of target-specific assembler and linker options (but not currently their default settings), use --target-help instead of --help=target.