llvm dev - Jan 2015 - [LLVMdev] CMake: Gold linker detection

I reacted as per my case.  You need CFLAGS in order to what linker you might be
using.

In case of clang, you can use “-fuse-ld” to control the invocation of linker.

In my opinion, it is not necessary to carry forward LDFLAGS unless you want to
control specific parts of the linker.

 

In my case, I have a cross compiler for ARM and I usually compile the code with

Clang –sysroot=<path_to_sysroot> --gcc-toolchain=<path_to_toolchain>
-target=<triple> file.c

Where I pass “–sysroot=<path_to_sysroot>
--gcc-toolchain=<path_to_toolchain> -target=<triple>” as
CMAKE_C_FLAGS :)

With out –gcc-toolchain, clang cannot find the linker and picks the system
linker which is usually /usr/bin/ld on a linux system.

 

 

--Sumanth G

From: C Bergström [mailto:cbergstrom at pathscale.com] 
Sent: Tuesday, January 27, 2015 11:51 AM
To: Sumanth Gundapaneni
Cc: llvmdev at cs.uiuc.edu; Rafael Ávila de Espíndola; Takumi NAKAMURA
Subject: Re: [LLVMdev] CMake: Gold linker detection

 

 

 

On Wed, Jan 28, 2015 at 2:27 AM, Sumanth Gundapaneni <sgundapa at
codeaurora.org <mailto:sgundapa at codeaurora.org> > wrote:

Hi Rafael,

                  I looked at the code which you pushed a while ago to check for
the gold linker.

Code below:

execute_process(

    COMMAND ${CMAKE_C_COMPILER} -Wl,--version

    OUTPUT_VARIABLE stdout 

    ERROR_QUIET)

  if("${stdout}" MATCHES "GNU gold")

    set(LLVM_LINKER_IS_GOLD ON)

  endif()

 

 

I was trying to build runtime libraries (compiler-rt) for ARM using “clang”
which includes this code.

A while ago, I saw the error message until geek4civic fixed it with
“ERROR_QUIET”.

I usually specify my sysroot and tool chain(linker) through CFLAGS. 

To fortify the logic, “${CMAKE_C_COMPILER} ${CMAKE_C_FLAGS}  -Wl, --version”
would be ideal than “${CMAKE_C_COMPILER}  -Wl, --version” which works mostly for
gnu compilers.

Let me know, I can push a patch 

 

execute_process(

-      COMMAND ${CMAKE_C_COMPILER} -Wl,--version

+    COMMAND “${CMAKE_C_COMPILER}  ${CMAKE_C_FLAGS}” -Wl,--version

    OUTPUT_VARIABLE stdout 

    ERROR_QUIET)

  if("${stdout}" MATCHES "GNU gold")

    set(LLVM_LINKER_IS_GOLD ON)

  endif()

 

While this may be convenient I don't think it's strictly correct.

 

CFLAGS != LDFLAGS

 

I think if extra flags are going to be passed it should be LD specific since
that's what this is intended to check.

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On Wed, Jan 28, 2015 at 7:00 AM, Sumanth Gundapaneni <
sgundapa at codeaurora.org> wrote:
> I reacted as per my case.  You need CFLAGS in order to what linker you
> might be using.
>
> In case of clang, you can use “-fuse-ld” to control the invocation of
> linker.
>
> In my opinion, it is not necessary to carry forward LDFLAGS unless you
> want to control specific parts of the linker.
>
Unless I'm mistaken typically LDFLAGS are passed like this. (I think you
are mistaken)

${COMPILER} ${LDFLAGS}

ld ${LDFLAGS} # It doesn't mean this isn't also possible

Regardless if you're dealing with a cross compiler or whatever weird CFLAGS
you have to pass. This is a linker issue and LDFLAGS are designed to deal
precisely with that.
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My bad. I agree with you.

 

--Sumanth G

From: C Bergström [mailto:cbergstrom at pathscale.com] 
Sent: Tuesday, January 27, 2015 10:16 PM
To: Sumanth Gundapaneni
Cc: llvmdev at cs.uiuc.edu; Rafael Ávila de Espíndola; Takumi NAKAMURA
Subject: Re: [LLVMdev] CMake: Gold linker detection

 

 

 

On Wed, Jan 28, 2015 at 7:00 AM, Sumanth Gundapaneni <sgundapa at
codeaurora.org <mailto:sgundapa at codeaurora.org> > wrote:

I reacted as per my case.  You need CFLAGS in order to what linker you might be
using.

In case of clang, you can use “-fuse-ld” to control the invocation of linker.

In my opinion, it is not necessary to carry forward LDFLAGS unless you want to
control specific parts of the linker.

 

Unless I'm mistaken typically LDFLAGS are passed like this. (I think you are
mistaken)

 

${COMPILER} ${LDFLAGS} 

 

ld ${LDFLAGS} # It doesn't mean this isn't also possible

 

Regardless if you're dealing with a cross compiler or whatever weird CFLAGS
you have to pass. This is a linker issue and LDFLAGS are designed to deal
precisely with that.

 

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