[PATCH 3/3] RISC-V: build: Allow LTO to be selected

[twd2]

Also, I tried `defconfig` with Full/Thin LTO.  It can boot and the
busybox shell works.

I'll put this information into the next version of the patch series.


Thanks.
Wende


On 2021/7/21 2:29, twd2 wrote:
> Hi, I just tried to compile with this patch and `allyesconfig` except
> COMPILE_TEST, FTRACE, KASAN, GCOV, and XFS [1].  It finishes with no
> issue, and takes ~22 min and ~25 GiB.  BTW, the kernel panics during boot
> even built with GCC, so I didn't do further tests :( .
>
> Command used: ARCH=riscv LLVM=1 LLVM_IAS=1 make HOSTCC=gcc vmlinux -j16
> Kernel version: commit 2734d6c1b1a0 ("Linux 5.14-rc2")
> LLVM version: commit 1b61d837b9d0 ("[Inline] Add test for PR50589 (NFC)")
> The `.config` file is attached.
>
> [1] https://github.com/ClangBuiltLinux/linux/issues/1215
>
> On 2021/7/20 5:25, Nick Desaulniers wrote:
>> On Mon, Jul 19, 2021 at 1:53 PM Wende Tan <twd2.me at gmail.com> wrote:
>>
>> Consider adding a little more detail to the commit message.
>>
>> In our experience with other architectures, we've hit numerous
>> compiler and kernel issues especially with allyesconfigs. Has that
>> been your experience with riscv?  It would be good to know if you've
>> hit issues with LTO plus certain configs, so that we have confirmation
>> others have seen these issues and so that we can triage fixes.
>>
>>> Signed-off-by: Wende Tan <twd2.me at gmail.com>
>>> ---
>>>  arch/riscv/Kconfig | 2 ++
>>>  1 file changed, 2 insertions(+)
>>>
>>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>>> index 8fcceb8eda07..b593e5031c79 100644
>>> --- a/arch/riscv/Kconfig
>>> +++ b/arch/riscv/Kconfig
>>> @@ -34,6 +34,8 @@ config RISCV
>>>         select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
>>>         select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
>>>         select ARCH_SUPPORTS_HUGETLBFS if MMU
>>> +       select ARCH_SUPPORTS_LTO_CLANG
>>> +       select ARCH_SUPPORTS_LTO_CLANG_THIN
>>>         select ARCH_USE_MEMTEST
>>>         select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU
>>>         select ARCH_WANT_FRAME_POINTERS
>>> --