From: Nick Desaulniers <ndesaulniers@google.com>
To: Nathan Chancellor <nathan@kernel.org>
Cc: paul.walmsley@sifive.com, palmer@dabbelt.com,
aou@eecs.berkeley.edu, conor@kernel.org, trix@redhat.com,
samitolvanen@google.com, twd2.me@gmail.com,
linux-riscv@lists.infradead.org, llvm@lists.linux.dev,
patches@lists.linux.dev
Subject: Re: [PATCH v3] RISC-V: build: Allow LTO to be selected
Date: Tue, 10 Oct 2023 10:03:15 -0700 [thread overview]
Message-ID: <CAKwvOdnMeM4YArw=hyVkev11cLfks5gaXWXNK+Wo0bcbeuMZHg@mail.gmail.com> (raw)
In-Reply-To: <20231003-riscv-lto-v3-1-8aca61a4ecb4@kernel.org>
On Tue, Oct 3, 2023 at 12:17 PM Nathan Chancellor <nathan@kernel.org> wrote:
>
> From: Wende Tan <twd2.me@gmail.com>
>
> Allow LTO to be selected for RISC-V, only when LLD >= 14, since there is an
> issue [1] in prior LLD versions that prevents LLD to generate proper
> machine code for RISC-V when writing `nop`s.
>
> I have tested enabling LTO for `defconfig`. The LLD took ~2m21s and ~3GiB
> on our Intel Xeon Gold 6140 server and produced an 18MiB Image. The image
> can boot to shell using an archriscv rootfs on QEMU.
>
> I have also tested it for `allyesconfig` without COMPILE_TEST, FTRACE,
> KASAN, and GCOV. The LLD took ~7h03m and ~335GiB on the server,
> successfully producing a 1.7GiB Image. Unfortunately, we cannot boot this
> image because the `create_kernel_page_table()` -> `alloc_pmd_early()` ->
> `BUG_ON()` logic limits the image to be < 1GiB. Maybe we can fix it in a
> separate patch further.
>
> Disable LTO for arch/riscv/kernel/pi, as llvm-objcopy expects an ELF
> object file when manipulating the files in that subfolder, rather than
> LLVM bitcode.
>
> [1] https://github.com/llvm/llvm-project/issues/50505, resolved by LLVM
> commit e63455d5e0e5 ("[MC] Use local MCSubtargetInfo in writeNops")
>
> Tested-by: Wende Tan <twd2.me@gmail.com>
> Signed-off-by: Wende Tan <twd2.me@gmail.com>
> Co-developed-by: Nathan Chancellor <nathan@kernel.org>
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Perhaps worth a v4 due to linker relaxation resulting in boot failures
you observed:
https://github.com/ClangBuiltLinux/linux/issues/1942 ?
--
Thanks,
~Nick Desaulniers
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next prev parent reply other threads:[~2023-10-10 17:03 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-03 19:16 [PATCH v3] RISC-V: build: Allow LTO to be selected Nathan Chancellor
2023-10-04 7:33 ` twd2
2023-10-04 9:51 ` Alexandre Ghiti
2023-10-04 15:21 ` Nathan Chancellor
2023-10-10 17:03 ` Nick Desaulniers [this message]
2023-10-10 19:52 ` Nathan Chancellor
2023-10-10 21:02 ` Conor Dooley
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