rengolin added a comment.
In http://reviews.llvm.org/D11153#204688, @logan wrote:
> Can't we simply rely on `--rtlib=compiler-rt`?
Specifically about --rtlib=compiler-rt, there are a few choices:
1. Assume RT == unwind + c++abi. This is good for architectures where those
libraries work reliably and are always available, either built in with Clang or
as a package. Since it's not easy to compile libc++abi, and it requires Clang
in the first place, I'd rather not have that until our build system is smart
enough to do a two-stage build, like GCC.
2. Assume RT is in a GNU system. This is what we have now, and to make debug,
profile and exception code work out-of-the-box, we need the libraries. I have
taken the bad choice of including both libgcc libraries.
3. Assume RT is just part of the compiler library. This would force users to
include -lgcc_s/-lunwind and/or -lgcc_eh/-lc++abi on every use of --rtlib.
Clang includes gcc_s/eh already when rtlib=libgcc (obviously), and so does GCC.
If we don't include some unwind/exception libraries with RT, the behaviour
would be very different and make build systems a lot more complex.
This change is a preparation for a bigger one. The plan is:
Allow tools to have default libraries on different systems. Something like:
void GetCompilerLibraries() {
// pick the defaults
switch(OS/Env) {
default:
llvm_unreachable("must have a default");
case GNU: // default GNU, --rtlib=libgcc
RT=libgcc; UNW=libgcc_s; EH=libgcc_eh;
case GNURT: // GNU with --rtlib=compiler-rt
RT=compiler-rt; UNW=libgcc_s; EH=libgcc_eh;
case FreeBSD: // BSD style
RT=compiler-rt; UNW=libunwind; EH=libc++abi;
case Darwin: // and so on...
RT=...
}
// override with arguments
for (lib : libArgs) {
if (lib == libunwind) UNW=lib;
else if (lib == libc++abi) EH=lib;
else if (lib == libgcc_s) UNW=lib;
else if (lib == libgcc_eh) UNW=lib;
}
}
This way you have complete flexibility, and still produce the expected default
results on all architectures.
GCC doesn't need that complexity because they're tied up with libgcc and
friends.
http://reviews.llvm.org/D11153
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