[cfe-dev] clang uses absolute path for linking compiler-rt libraries

[Manoj Gupta via cfe-dev]

Hi,

When using compiler-rt with clang, clang uses abolute path of compiler-rt
libraries to pass to linker
e.g. $ clang -v -rtlib=compiler-rt main.o -o main
"/usr/bin/x86_64-pc-linux-gnu-ld" ....  -lc
/usr/lib64/clang/6.0.0/lib/linux/libclang_rt.builtins-x86_64.a

Is there any particular reason clang does not use the format "-L/path" and
"-lname" e.g. -L/usr/lib64/clang/6.0.0/lib/linux -lclang_rt.builtins-x86_64?
I assume there must be a good reason but could not find one by searching
llvm-dev archives (I might  be searching using wrong keywords).

The reason I am asking is certain build tools like libtool parses "-l" or
"-L" strings in compiler's output to determine the default compiler
libraries. Since compiler-rt libraries are specified using absolute path,
it doesn't add compiler-rt libraries to its list of libs that must be
explicitly linked. The missing libraries becomes an issue if  final linking
is done with -nostdlib since the generated binary will miss the symbols
provided by builtins.

For reference, these are some of the ChromeOS bugs where we faced this
issue https://crbug.com/749263, https://crbug.com/802091.

Thanks,
Manoj
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