Unlike most of the other platforms supported by Clang, CloudABI only
supports static linkage, for the reason that global filesystem access is
prohibited. Functions provided by dlfcn.h are not present. As we know
that applications will not try to do any symbol lookups at run-time, we
can garbage collect unused code quite aggressively. Because of this, it
makes sense to enable -ffunction-sections and -fdata-sections by
default.
Object files will be a bit larger than usual, but the resulting binary
will not be affected, as the sections are merged again. However, when
--gc-sections is used, the linker is able to remove unused code far more
more aggressively. It also has the advantage that transitive library
dependencies only need to be provided to the linker in case that
functionality is actually used.
Differential Revision: http://reviews.llvm.org/D8635
Reviewed by: echristo
llvm-svn: 233299
Now that CloudABI's target information and header search logic for Clang
has been submitted, the only thing that remains to be done is adding
support for CloudABI's linker.
CloudABI uses Binutils ld, although there is some work to use lld
instead. This means that this code is largely based on what we use on
FreeBSD. There are some exceptions, however:
- Only static linking is performed. CloudABI does not support any
dynamically linked executables.
- CloudABI uses compiler-rt, libc++ and libc++abi unconditionally. Link
in these libraries instead of using libgcc_s, libstdc++, etc.
- We must ensure that the .eh_frame_hdr is present to make C++
exceptions work properly.
Differential Revision: http://reviews.llvm.org/D8250
llvm-svn: 233269
Ed Schouten