Re: [PATCH 3/3] BaseTools GCC: add the compiler flags to the linker command line

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 17 August 2016 at 13:38, Shi, Steven <steven.shi@intel.com> wrote:
> Hi Ard,
>
> CLANG38 has a build failure as below for this patch. This failure is because
> the CLANG38 enable the LTO through LLVMgold.so linker plugin, but the
> LLVMgold.so plugin cannot accept the clang -Oz cc flag as build option.
> After CC_FLAG is added in the link rule, the LLVMgold.so plugin reports link
> error. LLVMgold.so only accept -O0~-O3, and you can see it in the LLVM gold
> plugin source code in below:
>

This is interesting. I tried enabling LTO with CLANG35 for AARCH64
(using a 3.7 binary) and I did not see this problem.

>
>
> http://llvm.org/svn/llvm-project/llvm/tags/RELEASE_380/final/tools/gold/gold-plugin.cpp
>
>
>
>                       if (opt[1] < '0' || opt[1] > '3')
>
> line173：        message(LDPL_FATAL, "Optimization level must be between 0
> and 3");
>
>
>
> I hope to know is it mandatory to add compiler CC_FLAG in the linker rule
> for you? If it is mandatory, I have to introduce a new link rule for CLANG38
> to remove the compiler CC_FLAG. What do you think?
>

Yes, it is mandatory. And I consider this a bug in Clang.

For example, the mcmodel=xxx parameter *must* be passed to the linker,
since the linker generates code itself under LTO, and needs to know
for which code model it is doing so.
The same applies to -fpie and -mstrict-align (although clang also
requires the -pie linker flag to generate correct code)

Could you try putting -O2 in the DLINK2_FLAGS for Clang 38? (i.e., so
that the last -O option the linker sees is not -Oz)

-- 
Ard.