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[RFC PATCH 3/3] LoongArch: Handle table jump option for RUST

Tiezhu Yang posted 3 patches 5 months ago
There is a newer version of this series
[RFC PATCH 3/3] LoongArch: Handle table jump option for RUST
Posted by Tiezhu Yang 5 months ago 
When compiling with LLVM and CONFIG_RUST is set, there exist objtool
warnings "sibling call from callable instruction with modified stack
frame" in rust/core.o and rust/kernel.o.

For this special case, the related object file shows that there is no
generated relocation section '.rela.discard.tablejump_annotate' for the
table jump instruction jirl, thus objtool can not know that what is the
actual destination address.

If the rustc has the option "-Cllvm-args=--loongarch-annotate-tablejump",
pass the option to enable jump table for objtool, otherwise it is better
to remain -Zno-jump-tables to keep compatibility with older rustc.

How to test:

(1) Please install rustc 1.78.0 (without annotate-tablejump option) or
1.87.0 (with annotate-tablejump option), do not use the latest version
for now, otherwise there may be build error:

     --> rust/kernel/lib.rs:331:13
      |
  331 |         loc.file_with_nul()
      |             ^^^^^^^^^^^^^ method not found in `&'a Location<'a>`

  error: aborting due to 1 previous error

(2) Execute the following command:

  $ rustup component add rust-src
  $ make LLVM=1 rustavailable
  $ make ARCH=loongarch LLVM=1 clean defconfig
  $ scripts/config -d MODVERSIONS \
    -e RUST -e SAMPLES -e SAMPLES_RUST \
    -e SAMPLE_RUST_CONFIGFS -e SAMPLE_RUST_MINIMAL \
    -e SAMPLE_RUST_MISC_DEVICE -e SAMPLE_RUST_PRINT \
    -e SAMPLE_RUST_DMA -e SAMPLE_RUST_DRIVER_PCI \
    -e SAMPLE_RUST_DRIVER_PLATFORM -e SAMPLE_RUST_DRIVER_FAUX \
    -e SAMPLE_RUST_DRIVER_AUXILIARY -e SAMPLE_RUST_HOSTPROGS
  $ make ARCH=loongarch LLVM=1 olddefconfig all

Suggested-by: WANG Rui <wangrui@loongson.cn>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---
 arch/loongarch/Kconfig  | 4 ++++
 arch/loongarch/Makefile | 6 ++++++
 2 files changed, 10 insertions(+)

diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index f0abc38c40ac..57933a717e92 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -298,6 +298,10 @@ config AS_HAS_LVZ_EXTENSION
 config CC_HAS_ANNOTATE_TABLEJUMP
 	def_bool $(cc-option,-mannotate-tablejump)
 
+config RUSTC_HAS_ANNOTATE_TABLEJUMP
+	depends on RUST
+	def_bool $(rustc-option,-Cllvm-args=--loongarch-annotate-tablejump)
+
 menu "Kernel type and options"
 
 source "kernel/Kconfig.hz"
diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
index 9d80af7f75c8..b26d47707031 100644
--- a/arch/loongarch/Makefile
+++ b/arch/loongarch/Makefile
@@ -106,6 +106,12 @@ KBUILD_CFLAGS			+= -mannotate-tablejump
 else
 KBUILD_CFLAGS			+= -fno-jump-tables # keep compatibility with older compilers
 endif
+ifdef CONFIG_RUSTC_HAS_ANNOTATE_TABLEJUMP
+# Pass '--loongarch-annotate-tablejump' via '-Cllvm-args' to rustc when RUST is enabled.
+KBUILD_RUSTFLAGS		+= -Cllvm-args=--loongarch-annotate-tablejump
+else
+KBUILD_RUSTFLAGS		+= -Zno-jump-tables # keep compatibility with older compilers
+endif
 ifdef CONFIG_LTO_CLANG
 # The annotate-tablejump option can not be passed to LLVM backend when LTO is enabled.
 # Ensure it is aware of linker with LTO, '--loongarch-annotate-tablejump' also needs to
-- 
2.42.0
Re: [RFC PATCH 3/3] LoongArch: Handle table jump option for RUST
Posted by Miguel Ojeda 5 months ago 
On Wed, Sep 3, 2025 at 11:53 AM Tiezhu Yang <yangtiezhu@loongson.cn> wrote:
>
> When compiling with LLVM and CONFIG_RUST is set, there exist objtool
> warnings "sibling call from callable instruction with modified stack
> frame" in rust/core.o and rust/kernel.o.

Thanks for fixing this! I have seen it for a long time in my CI:

I think this is:

    Reported-by: Miguel Ojeda <ojeda@kernel.org>
    Closes: https://lore.kernel.org/rust-for-linux/CANiq72mNeCuPkCDrG2db3w=AX+O-zYrfprisDPmRac_qh65Dmg@mail.gmail.com/

Perhaps consider adding an example of the warning in the log for
future Lore searches:

    rust/core.o: warning: objtool:
_RNvXs1_NtNtCs5QSdWC790r4_4core5ascii10ascii_charNtB5_9AsciiCharNtNtB9_3fmt5Debug3fmt+0x54:
sibling call from callable instruction with modified stack frame

> (1) Please install rustc 1.78.0 (without annotate-tablejump option) or
> 1.87.0 (with annotate-tablejump option), do not use the latest version
> for now, otherwise there may be build error:

Nightly is not a released version, and it is expected that it breaks
from time to time. Even beta may break. We are ~2 months away from
that release.

In any case, I don't think this information is related to this commit.

> +config RUSTC_HAS_ANNOTATE_TABLEJUMP
> +       depends on RUST
> +       def_bool $(rustc-option,-Cllvm-args=--loongarch-annotate-tablejump)

I think this may be fine given it is `-Cllvm-args` and anyway
LoongArch doesn't use a `target.json` (which is great!), but please
double-check reading what I wrote in 46e24a545cdb ("rust:
kasan/kbuild: fix missing flags on first build") just in case.

I hope this helps!

Cheers,
Miguel
Re: [RFC PATCH 3/3] LoongArch: Handle table jump option for RUST
Posted by Tiezhu Yang 5 months ago 
On 2025/9/3 下午6:28, Miguel Ojeda wrote:
> On Wed, Sep 3, 2025 at 11:53 AM Tiezhu Yang <yangtiezhu@loongson.cn> wrote:
>>
>> When compiling with LLVM and CONFIG_RUST is set, there exist objtool
>> warnings "sibling call from callable instruction with modified stack
>> frame" in rust/core.o and rust/kernel.o.
> 
> Thanks for fixing this! I have seen it for a long time in my CI:
> 
> I think this is:
> 
>      Reported-by: Miguel Ojeda <ojeda@kernel.org>
>      Closes: https://lore.kernel.org/rust-for-linux/CANiq72mNeCuPkCDrG2db3w=AX+O-zYrfprisDPmRac_qh65Dmg@mail.gmail.com/
> 
> Perhaps consider adding an example of the warning in the log for
> future Lore searches:
> 
>      rust/core.o: warning: objtool:
> _RNvXs1_NtNtCs5QSdWC790r4_4core5ascii10ascii_charNtB5_9AsciiCharNtNtB9_3fmt5Debug3fmt+0x54:
> sibling call from callable instruction with modified stack frame

OK, will update the commit message in the next version.

>> (1) Please install rustc 1.78.0 (without annotate-tablejump option) or
>> 1.87.0 (with annotate-tablejump option), do not use the latest version
>> for now, otherwise there may be build error:
> 
> Nightly is not a released version, and it is expected that it breaks
> from time to time. Even beta may break. We are ~2 months away from
> that release.
> 
> In any case, I don't think this information is related to this commit.

OK, I will remove the above info in the commit message.

>> +config RUSTC_HAS_ANNOTATE_TABLEJUMP
>> +       depends on RUST
>> +       def_bool $(rustc-option,-Cllvm-args=--loongarch-annotate-tablejump)
> 
> I think this may be fine given it is `-Cllvm-args` and anyway
> LoongArch doesn't use a `target.json` (which is great!), but please
> double-check reading what I wrote in 46e24a545cdb ("rust:
> kasan/kbuild: fix missing flags on first build") just in case.

OK, will do.

Thanks,
Tiezhu

Patchew 2.1-devel-b67e4c2

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