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[libcxx] Make it drastically simpler to link libc++.
Summary: Currently on most platforms you have to manually link the c++ abi library used with libc++ whenever you use libc++. So your typical libc++ command like invocation might look like: ``` clang++ -stdlib=libc++ foo.cpp -lc++abi ``` Having to manually link `libc++abi.so` makes it harder for libc++ to be used generically. This patch fixes that by generating a linker script for `libc++.so` that correctly links the ABI library. On linux the linker script for libc++abi would look like: ``` # libc++.so INPUT(libc++.so.1 -lc++abi) ``` With the linker script you can now use libc++ using only `-stdlib=libc++`. This is the technique that is used on FreeBSD in ordered to link cxxrt and I think it's the best approach to make our users lives simpler. The CMake option used to enable this is `LIBCXX_ENABLE_ABI_LINKER_SCRIPT`. In future I would like to enable this by default on all platforms except for Darwin. Reviewers: mclow.lists, danalbert, rsmith, jroelofs, EricWF Subscribers: cfe-commits Differential Revision: http://reviews.llvm.org/D12508 llvm-svn: 250319
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,79 @@ | ||
| #!/usr/bin/env python | ||
| import os | ||
| import sys | ||
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| def print_and_exit(msg): | ||
| sys.stderr.write(msg + '\n') | ||
| sys.exit(1) | ||
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| def usage_and_exit(): | ||
| print_and_exit("Usage: ./gen_link_script.py [--help] [--dryrun] <path/to/libcxx.so> <abi_libname>") | ||
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| def help_and_exit(): | ||
| help_msg = \ | ||
| """Usage | ||
| gen_link_script.py [--help] [--dryrun] <path/to/libcxx.so> <abi_libname> | ||
| Generate a linker script that links libc++ to the proper ABI library. | ||
| The script replaces the specified libc++ symlink. | ||
| An example script for c++abi would look like "INPUT(libc++.so.1 -lc++abi)". | ||
| Arguments | ||
| <path/to/libcxx.so> - The top level symlink to the versioned libc++ shared | ||
| library. This file is replaced with a linker script. | ||
| <abi_libname> - The name of the ABI library to use in the linker script. | ||
| The name must be one of [c++abi, stdc++, supc++, cxxrt]. | ||
| Exit Status: | ||
| 0 if OK, | ||
| 1 if the action failed. | ||
| """ | ||
| print_and_exit(help_msg) | ||
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| def parse_args(): | ||
| args = list(sys.argv) | ||
| del args[0] | ||
| if len(args) == 0: | ||
| usage_and_exit() | ||
| if args[0] == '--help': | ||
| help_and_exit() | ||
| dryrun = '--dryrun' == args[0] | ||
| if dryrun: | ||
| del args[0] | ||
| if len(args) != 2: | ||
| usage_and_exit() | ||
| symlink_file = args[0] | ||
| abi_libname = args[1] | ||
| return dryrun, symlink_file, abi_libname | ||
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| def main(): | ||
| dryrun, symlink_file, abi_libname = parse_args() | ||
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| # Check that the given libc++.so file is a valid symlink. | ||
| if not os.path.islink(symlink_file): | ||
| print_and_exit("symlink file %s is not a symlink" % symlink_file) | ||
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| # Read the symlink so we know what libc++ to link to in the linker script. | ||
| linked_libcxx = os.readlink(symlink_file) | ||
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| # Check that the abi_libname is one of the supported values. | ||
| supported_abi_list = ['c++abi', 'stdc++', 'supc++', 'cxxrt'] | ||
| if abi_libname not in supported_abi_list: | ||
| print_and_exit("abi name '%s' is not supported: Use one of %r" % | ||
| (abi_libname, supported_abi_list)) | ||
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| # Generate the linker script contents and print the script and destination | ||
| # information. | ||
| contents = "INPUT(%s -l%s)" % (linked_libcxx, abi_libname) | ||
| print("GENERATING SCRIPT: '%s' as file %s" % (contents, symlink_file)) | ||
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| # Remove the existing libc++ symlink and replace it with the script. | ||
| if not dryrun: | ||
| os.unlink(symlink_file) | ||
| with open(symlink_file, 'w') as f: | ||
| f.write(contents + "\n") | ||
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| if __name__ == '__main__': | ||
| main() |