When you use cc(1) to link a program, it will invoke a default linker command. For instance, your version of the compiler may have been built to use /usr/bin/ld by default on a Unix-like platform.
Is there a way to specify a different linker command that cc(1) (or c++(1)) should use (e.g., /usr/local/bin/ld instead of /usr/bin/ld)? I'm interested mostly in GCC and Clang.
I'm not looking for methods that involve running the various compilation steps separately (e.g., pre-process, compile, assemble, and link).
For example, I was hoping something like this might do the job:
env LD=/usr/local/bin/ld cc foo.c -o foo
But that doesn't work for GCC or Clang. It would work, of course, if you had a makefile that built an object file first, and then invoked ${LD} to link (e.g., env LD=/usr/local/bin/ld make).
With one possible motivation, to easily test with a different linker than the default linker. For example, it would be nice to be able to do this:
cc --linker=/usr/local/bin/ld foo.c -o foo
Instead, you have to do generate the object file, run cc -v to figure out the arguments to ld, and manually run the ld you want with those arguments:
cc -c foo.c
cc -v foo.c -o /dev/null
Now look at the linker invocation and manually copy/paste replacing linker and temporary object file. Something like this (example taken from a test on fedora 23) where you replace /usr/libexec/gcc/x86_64-redhat-linux/5.3.1/collect2 with /usr/local/bin/ld (although it's not exactly the same as collect2):
/usr/local/bin/ld -plugin /usr/libexec/gcc/x86_64-redhat-linux/5.3.1/liblto_plugin.so -plugin-opt=/usr/libexec/gcc/x86_64-redhat-linux/5.3.1/lto-wrapper -plugin-opt=-fresolution=/tmp/jhein/ccM2XKIg.res -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lc -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lgcc_s --build-id --no-add-needed --eh-frame-hdr --hash-style=gnu -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o c /usr/lib/gcc/x86_64-redhat-linux/5.3.1/../../../../lib64/crt1.o /usr/lib/gcc/x86_64-redhat-linux/5.3.1/../../../../lib64/crti.o /usr/lib/gcc/x86_64-redhat-linux/5.3.1/crtbegin.o -L/usr/lib/gcc/x86_64-redhat-linux/5.3.1 -L/usr/lib/gcc/x86_64-redhat-linux/5.3.1/../../../../lib64 -L/lib/../lib64 -L/usr/lib/../lib64 -L/usr/lib/gcc/x86_64-redhat-linux/5.3.1/../../.. c.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib/gcc/x86_64-redhat-linux/5.3.1/crtend.o /usr/lib/gcc/x86_64-redhat-linux/5.3.1/../../../../lib64/crtn.o
As you can see, that's not easy. Note there is documentation in the GCC information page about how collect2 looks for a linker program. But according to those documentation, the first place it looks is not an environment variable or something you can specify on the command line (e.g., --linker). The documentation says it looks first for a "a hard coded linker file name". If that documentation is correct, to coerce it not to use that linker (i.e., trick it), you would have to rename the default linker (e.g., sudo mv /usr/bin/ld /usr/bin/ld.tmp-disable).
Using -B seems to work well enough for my needs.
The -B option allows you to specify an alternate search path for executables, libraries, include files & data files that the compiler will use. This works for some versions of GCC 1 and for Clang (currently undocumented; it is in the man pages of at least Clang 3.7 and 3.8):
cc -B/usr/local/bin foo.c -o foo
Note that this will cause cc to search for other tools (e.g., the assembler) in the path specified by -B. So supposing you have a different version of binutils installed in /usr/local/bin. If you only want to use that linker (rather than /usr/local/bin/as, et. al.), you could do something like this:
mkdir /tmp/usemyld
ln -s /usr/local/bin/ld /tmp/usemyld
cc -B/tmp/usemyld foo.c -o foo
-B has its own set of rules that allows you to override different files that the GCC compiler tries to use (programs, libraries, include files, data files).
This is documented as far back as at least GCC 2.95 (1999-07-31); read the GCC man / info pages. I don't know how compatible the behavior of -B is for clang. As mentioned, it's not currently documented in the clang man page. But it worked well enough to allow me to select an alternate linker as shown above.
gcc also supports calling a script/program as specified by -wrapper. clang does not (currently). You could also use that and point at a wrapper script that alters what program the compiler is calling. I don't know if collect2 heeds the -wrapper option (and for gcc, collect2 is what calls the linker when compiling c/c++ programs at least).
1 The linker search order documented in the gcc info page for collect2 says that it will search first for "a hard coded linker file name if GCC was configured with the '--with-ld' option"). So if your gcc was not configured with '--with-ld', then it will eventually search in the path specified by -B (if it doesn't find real-ld first). If your gcc was configured with --with-ld, then the -B option will not help you specify an alternate linker of your choosing.