11.3. Extracting flags from the wrapper compilers

If you cannot use the wrapper compiler for some reason, there are multiple supported ways to extract the compiler/linker flags that you will need.

11.3.1. Using the --showme option

The wrapper compiler supports a --showme command line option that will show what commands would have been invoked.


If you pass --showme and additional command line parameters to the wrapper compiler, be sure to also pass in a filename. Otherwise, the --showme functionality will not display output as expected.


It is almost never a good idea to hard-code these results in a Makefile (or other build system). It is almost always best to run (for example) pmixcc --showme:compile in a dynamic fashion to find out what you need. For example, GNU Make allows running commands and assigning their results to variables:

PMIX_COMPILE_FLAGS = $(shell pmixcc --showme:compile)
PMIX_LINK_FLAGS = $(shell pmixcc --showme:link)

my_app: my_app.c
        $(CC) $(PMIX_COMPILE_FLAGS) my_app.c $(PMIX_LINK_FLAGS) -o my_app

11.3.2. Using pkg-config

Alternatively, PMIx also installs pkg-config(1) configuration files under $libdir/pkgconfig. If pkg-config is configured to find these files (e.g., if you add $libdir/pkgconfig — which is usually $prefix/lib/pkgconfig — to the PKG_CONFIG_PATH environment variable), then compiling / linking PMIx programs can be performed like this:

shell$ export PKG_CONFIG_PATH=/opt/pmix/lib/pkgconfig
shell$ gcc hello_world.c -o hello_world -g \
            `pkg-config pmix --cflags --libs`


PMIx’s pkg-config file works properly, but it probably isn’t technically correct.

Specifically: PMIx will list all of its dependent libraries that are necessary to link PMIx-based application, even if a given dependency has a .pc file and should therefore be listed as a Requires and/or Requires.private in PMIx’s .pc files.

For example, PMIx lists -lhwloc in both Libs and Libs.private. But since HWLOC provides its own pmix.pc file, it would be more correct for PMIx to not list -lhwloc in Libs / Libs.private, and instead include:

Requires: hwloc
Requires.private: hwloc

The end result is likely immaterial, but we document this just in case it ever becomes an issue someday.

11.3.3. Using pmix_info

This method is not directly suitable for getting all the compiler / linker flags needed to compile PMIx-based applications because it does not include the relevant flags to find PMIx’s headers and libraries. But it does show a breakdown of all other flags.

shell$ pmix_info --all | grep Build
         Build CFLAGS:
        Build LDFLAGS:
           Build LIBS: -ldl -levent_core -levent_pthreads -lhwloc

This installation is only adding options in the xLIBS areas of the wrapper compilers; all other values are blank (remember: the -I’s and -L’s are implicit).

Note that the --parsable option can be used to obtain machine-parsable versions of this output. For example:

shell$ ompi_info --all --parsable | grep option:build
     option:build:libs:-ldl -levent_core -levent_pthreads -lhwloc