For a GCC or Clang command, there is typically one primary outputfile, specified by -o or the default (a.out ora.exe). There can also be temporary files and auxiliaryfiles.

Primary output file

We can specify the primary output file with the -ooption. When unspecified, a default output file name is inferred fromthe input files and the final phase. When the final phase is linking,the default output file name is a.out ora.exe.

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gcc -S d/a.c      # a.s
gcc -c d/a.c      # a.o
gcc d/a.c         # a.out
gcc d/a.c -o e/a  # e/a

Temporary files

For compilation and linking in one command, the relocatable objectfiles are temporary files.

For GCC, when generating a relocatable object file, it needs togenerate a temporary assembly file, then feeds it to GNU assembler.

We can set the temporary directory with one of the environmentvariables TMPDIR, TMP, and TEMP.When none is specified, compilers have a fallback, /tmp on*NIX systems.

Auxiliary files

Beside primary output files and temporary output files, we have athird output file type called auxiliary output files. Some options suchas -ftest-coverage and -gsplit-dwarfcause the compiler to generate auxiliary output files.

For compilation without linking (-c, -S,etc), the auxiliary output file names are derived from the primaryoutput file name.

For compilation and linking in one command, the primary output filename affects the auxiliary output file names.

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gcc -c -g -gsplit-dwarf d/a.c d/b.c      # a.o b.o a.dwo b.dwo
gcc -c -g -gsplit-dwarf d/a.c -o e/a.o   # e/a.o e/a.dwo
gcc -g -gsplit-dwarf d/a.c d/b.c -o e/x  # e/x (temporary .o files) e/x-a.dwo e/x-b.dwo
gcc -g -gsplit-dwarf d/a.c d/b.c         # (temporary .o files) a-a.dwo a-b.dwo

GCC provides some optionsthat are primarily of interest to GCC developers. These dump outputfiles are treated the same way as auxiliary output files.

-dumpdir and -dumpbase are provided tocontrol the auxiliary output file names. The officialdocumentation may be difficult to follow. Let's see someexamples.

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gcc -g -gsplit-dwarf -dumpdir f d/a.c -c # fa.dwo
gcc -g -gsplit-dwarf -dumpdir f d/a.c    # fa.dwo
gcc -g -gsplit-dwarf -dumpdir f/ d/a.c   # f/a.dwo
gcc -g -gsplit-dwarf -dumpbase f d/a.c   # f-a.dwo
gcc -g -gsplit-dwarf -dumpbase f/ d/a.c  # f/-a.dwo

# Specify both to avoid the influence of the source filename.
gcc -g -gsplit-dwarf -dumpdir f/ -dumpbase x d/a.c  # f/x.dwo

In the absence of -dumpdir, -dumpbaseappends a dash, which makes it inconvenient.

I suggest that you only use -dumpdir.

I have a patch to support -dumpdir in Clang: https://reviews.llvm.org/D149193.

-save-temps

-save-tempsand -save-temps={cwd,obj} generate intermediatefiles.

In the absence of -dumpdir/-dumpbase,-save-temps is like an alias for-save-temps=cwd and stores intermediate files in thecurrent directory. -save-temps=obj stores intermediatefiles in the directory of the output file specified by-o.

When -dumpdir is specified, there is complex interactionbetween -dumpdir and-save-temps/-save-temps={cwd,obj}. For Clang,I think we should make -dumpdir and-save-temps/-save-temps={cwd,obj}orthogonal.

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# The last of -dumpdir and -save-temps wins.
gcc -g -gsplit-dwarf d/a.c -o e/x -dumpdir f/ -save-temps=obj # e/a.{i,s,o,dwo}
gcc -g -gsplit-dwarf d/a.c -o e/x -save-temps=obj -dumpdir f/ # f/a.{i,s,o,dwo}

# -save-temps=obj and -dumpdir are orthogonal.
clang -g -gsplit-dwarf d/a.c -o e/x -save-temps=obj -dumpdir f/ # e/a.{i,s,o} f/a.dwo

Other auxiliary files

Clang supports a few options (e.g. -ftime-trace) togenerate other auxiliary output files. I plan to change their file namesto be controlled by -dumpdir.