./configure compiler-rt patch

./configure compiler-rt patch

[Matúš Olekšák]

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Hi,
I have complete LLVM toolchain and I discovered that, detection of
compiler-rt is not working in ./configure. Because it is looking for
dynamic library compiler_rt but it doesn't exist. Instead it should ask
compiler about libgcc-file-name to get correct filename. I attached patch
to fix this issue.

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--- a/configure
+++ b/configure
@@ -597,7 +597,8 @@
 
 # Find compiler runtime library
 test -z "$LIBCC" && tryldflag LIBCC -lgcc && tryldflag LIBCC -lgcc_eh
-test -z "$LIBCC" && tryldflag LIBCC -lcompiler_rt
+test -z "$LIBCC" && try_libcc=`$CC -print-libgcc-file-name 2>/dev/null` \
+                 && tryldflag LIBCC "$try_libcc"
 test -z "$LIBCC" && try_libcc=`$CC -print-file-name=libpcc.a 2>/dev/null` \
                  && tryldflag LIBCC "$try_libcc"
 printf "using compiler runtime libraries: %s\n" "$LIBCC"

Re: ./configure compiler-rt patch

[Rich Felker]

On Tue, Feb 13, 2018 at 03:53:39PM +0100, Matúš Olekšák wrote:
> Hi,
> I have complete LLVM toolchain and I discovered that, detection of
> compiler-rt is not working in ./configure. Because it is looking for
> dynamic library compiler_rt but it doesn't exist. Instead it should ask
> compiler about libgcc-file-name to get correct filename. I attached patch
> to fix this issue.

> --- a/configure
> +++ b/configure
> @@ -597,7 +597,8 @@
>  
>  # Find compiler runtime library
>  test -z "$LIBCC" && tryldflag LIBCC -lgcc && tryldflag LIBCC -lgcc_eh
> -test -z "$LIBCC" && tryldflag LIBCC -lcompiler_rt
> +test -z "$LIBCC" && try_libcc=`$CC -print-libgcc-file-name 2>/dev/null` \
> +                 && tryldflag LIBCC "$try_libcc"
>  test -z "$LIBCC" && try_libcc=`$CC -print-file-name=libpcc.a 2>/dev/null` \
>                   && tryldflag LIBCC "$try_libcc"
>  printf "using compiler runtime libraries: %s\n" "$LIBCC"

Sorry for the slow response. I think this probably okay, but if I
remember right, there has been discussion of this before and might be
more subtlety to doing it optimally. The nice property of the -lgcc
case (and the -lcompiler_rt case if it worked, but it doesn't) is that
it's immune to changes in compiler version; upgrading gcc without
rerunning configure won't cause it to fail.

It might be optimal to try the basename produced by
-print-libgcc-file-name, stripping the "lib" and ".a" parts and using
it with -l, to see if that works. But it might not actually work for
anything other than gcc. I know it doesn't (or at least didn't in the
past) work for pcc.

Note that -print-libgcc-file-name does work with pcc, at least modern
versions, so I think we could remove the pcc-specific check too at
some point.

Rich

Re: ./configure compiler-rt patch

[Shiz]

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> On 21 Feb 2018, at 03:12, Rich Felker <dalias@libc.org> wrote:
> 
> It might be optimal to try the basename produced by
> -print-libgcc-file-name, stripping the "lib" and ".a" parts and using
> it with -l, to see if that works. But it might not actually work for
> anything other than gcc. I know it doesn't (or at least didn't in the
> past) work for pcc.

Sadly, that won’t work for clang, to the best of my knowledge.
Quickly tested on a macOS machine, but I think it’s the same anywhere:

~ » clang -rtlib=compiler-rt -print-libgcc-file-name
/Applications/.../usr/lib/clang/9.0.0/lib/darwin17.4.0/libclang_rt.builtins-x86_64.a
~ » clang -lclang_rt.builtins-x86_64
ld: library not found for -lclang_rt.builtins-x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

I’m fairly sure -lcompiler_rt used to work at some point, but it seems
they stripped support, which makes sense given that compiler-rt is
actually multiple things now, and this would refer to the builtins part
of it.

- Shiz

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Re: ./configure compiler-rt patch

[Dmitry Golovin]

21.02.2018, 12:30, "Shiz" <hi@shiz.me>:
>>  On 21 Feb 2018, at 03:12, Rich Felker <dalias@libc.org> wrote:
>>
>>  It might be optimal to try the basename produced by
>>  -print-libgcc-file-name, stripping the "lib" and ".a" parts and using
>>  it with -l, to see if that works. But it might not actually work for
>>  anything other than gcc. I know it doesn't (or at least didn't in the
>>  past) work for pcc.
>
> Sadly, that won’t work for clang, to the best of my knowledge.
> Quickly tested on a macOS machine, but I think it’s the same anywhere:
>
> ~ » clang -rtlib=compiler-rt -print-libgcc-file-name
> /Applications/.../usr/lib/clang/9.0.0/lib/darwin17.4.0/libclang_rt.builtins-x86_64.a
> ~ » clang -lclang_rt.builtins-x86_64
> ld: library not found for -lclang_rt.builtins-x86_64
> clang: error: linker command failed with exit code 1 (use -v to see invocation)
>
> I’m fairly sure -lcompiler_rt used to work at some point, but it seems
> they stripped support, which makes sense given that compiler-rt is
> actually multiple things now, and this would refer to the builtins part
> of it.
>
> - Shiz

I can confirm on Linux with my toolchain:
$ clang -print-libgcc-file-name
/x86_64-pc-linux-musl/lib/clang/7.0.0/lib/linux/libclang_rt.builtins-x86_64.a
$ clang -lclang_rt.builtins-x86_64
/x86_64-pc-linux-musl/bin/ld.lld: error: unable to find library -lclang_rt.builtins-x86_64
clang-7.0: error: linker command failed with exit code 1 (use -v to see invocation)

The workaround would be then:
$ clang -L/x86_64-pc-linux-musl/lib/clang/7.0.0/lib/linux -lclang_rt.builtins-x86_64

In general case it comes to:
$ LIBGCCPATH="$(clang -print-libgcc-file-name)"
$ LIBGCCDIR="${LIBGCCPATH%/*}"
$ LIBGCCFILE="${LIBGCCPATH##*/lib}"
$ clang -L$LIBGCCDIR -l${LIBGCCFILE%*.a}

As a person who compiles musl with compiler-rt, I want this patch to be merged, because right now I set LIBCC="$(clang -print-libgcc-file-name)" parameter to musl's configure anyway.

Regards,
Dmitry

./configure compiler-rt patch

[Matúš Olekšák]

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Hi,
I have complete LLVM toolchain and I discovered that, detection of
compiler-rt is not working in ./configure. Because it is looking for
dynamic library compiler_rt but it doesn't exist. Instead it should ask
compiler about libgcc-file-name to get correct filename. I attached patch
to fix this issue.

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[-- Attachment #2: compiler-rt.patch --]
[-- Type: text/x-patch, Size: 519 bytes --]

--- a/configure
+++ b/configure
@@ -597,7 +597,8 @@
 
 # Find compiler runtime library
 test -z "$LIBCC" && tryldflag LIBCC -lgcc && tryldflag LIBCC -lgcc_eh
-test -z "$LIBCC" && tryldflag LIBCC -lcompiler_rt
+test -z "$LIBCC" && try_libcc=`$CC -print-libgcc-file-name 2>/dev/null` \
+                 && tryldflag LIBCC "$try_libcc"
 test -z "$LIBCC" && try_libcc=`$CC -print-file-name=libpcc.a 2>/dev/null` \
                  && tryldflag LIBCC "$try_libcc"
 printf "using compiler runtime libraries: %s\n" "$LIBCC"