[PATCH v3 0/1] RISC-V: enable rust

[PATCH v3 0/1] RISC-V: enable rust

[Conor Dooley]

From: Conor Dooley <conor.dooley@microchip.com>

I've intentionally not turned on the gcc support, as discussed on
v1. I've also switched over to using the target, but it is a bit heavier
than the one arm64 seems to be using. RISC-V has fewer targets available
and this was the closest. I preserved the redzone disabling, just moved
into the Makefile. Any comment from Gary or the LLVM lads on the target
would be great I think:
https://github.com/rust-lang/rust/blob/master/compiler/rustc_target/src/spec/targets/riscv64imac_unknown_none_elf.rs
arm64 is using:
https://github.com/rust-lang/rust/blob/master/compiler/rustc_target/src/spec/targets/aarch64_unknown_none.rs

I was gonna send this yesterday, but found out last minute I had invalid
code in the target generation script. The kernel test robot had given my
branch the global all-clear - the rust coverage with all the
"depends on !FOO" must really limit the build coverage. I built for x86
with rust enabled locally this time to make sure..

As this as lifted from the state of the Rust-for-Linux tree, the commit
messages from there cannot be preserved, so these patches have commit
messages that I wrote.

I've tested this on Icicle, and the modules seem to work as expected.
Unfortunately there appear to be implicit 32-bit divisions (or similar)
in core Rust code, so, as in the downstream Rust-for-Linux tree, Rust is
only enabled for 64-bit.

Thanks,
Conor.

Changes in v3:
- Use a builtin target and modify it in kbuild
- Drop the kCFI patch, that's been merged independently

Changes in v2:
- Rebase, since a good bit of time has passed!
- Add the extra patch, disabling when CFI_CLANG is enabled.

Changes in v1:
- rebase on v6.3-rc1
- resort the `um` entry in the arch-support table while adding RISC-V
  to it
- drop 32-bit bits
- have another crack at assigning authorship

Changes in RFC-RESEND:
- fix the asymmetrical additions in the Makefile bits
- add cc-cover to my git send-email command...

CC: Miguel Ojeda <ojeda@kernel.org>
CC: Alex Gaynor <alex.gaynor@gmail.com>
CC: Wedson Almeida Filho <wedsonaf@gmail.com>
CC: Boqun Feng <boqun.feng@gmail.com>
CC: Gary Guo <gary@garyguo.net>
CC: Björn Roy Baron <bjorn3_gh@protonmail.com>
CC: Jonathan Corbet <corbet@lwn.net>
CC: Paul Walmsley <paul.walmsley@sifive.com>
CC: Palmer Dabbelt <palmer@dabbelt.com>
CC: Nathan Chancellor <nathan@kernel.org>
CC: Nick Desaulniers <ndesaulniers@google.com>
CC: rust-for-linux@vger.kernel.org
CC: linux-doc@vger.kernel.org
CC: linux-kernel@vger.kernel.org
CC: linux-riscv@lists.infradead.org
CC: llvm@lists.linux.dev

Miguel Ojeda (1):
  RISC-V: enable building 64-bit kernels with rust support

 Documentation/rust/arch-support.rst | 1 +
 arch/riscv/Kconfig                  | 1 +
 arch/riscv/Makefile                 | 7 +++++++
 scripts/generate_rust_target.rs     | 6 ++++++
 4 files changed, 15 insertions(+)

-- 
2.43.0

[PATCH v3 1/1] RISC-V: enable building 64-bit kernels with rust support

[Conor Dooley]

From: Miguel Ojeda <ojeda@kernel.org>

The rust modules work on 64-bit RISC-V, with no twiddling required.
Select HAVE_RUST and provide the required flags to kbuild so that the
modules can be used. The Makefile and Kconfig changes are lifted from
work done by Miguel in the Rust-for-Linux tree, hence his authorship.
Following the rabbit hole, the Makefile changes originated in a script,
created based on config files originally added by Gary, hence his
co-authorship.

32-bit is broken in core rust code, so support is limited to 64-bit:
ld.lld: error: undefined symbol: __udivdi3

As 64-bit RISC-V is now supported, add it to the arch support table.

Co-developed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Co-developed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
---
 Documentation/rust/arch-support.rst | 1 +
 arch/riscv/Kconfig                  | 1 +
 arch/riscv/Makefile                 | 7 +++++++
 scripts/generate_rust_target.rs     | 6 ++++++
 4 files changed, 15 insertions(+)

diff --git a/Documentation/rust/arch-support.rst b/Documentation/rust/arch-support.rst
index 5c4fa9f5d1cd..4d1495ded2aa 100644
--- a/Documentation/rust/arch-support.rst
+++ b/Documentation/rust/arch-support.rst
@@ -17,6 +17,7 @@ Architecture   Level of support  Constraints
 =============  ================  ==============================================
 ``arm64``      Maintained        Little Endian only.
 ``loongarch``  Maintained        -
+``riscv``      Maintained        ``riscv64`` only.
 ``um``         Maintained        ``x86_64`` only.
 ``x86``        Maintained        ``x86_64`` only.
 =============  ================  ==============================================
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index be09c8836d56..cad31864fd0f 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -155,6 +155,7 @@ config RISCV
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_RETHOOK if !XIP_KERNEL
 	select HAVE_RSEQ
+	select HAVE_RUST if 64BIT
 	select HAVE_SAMPLE_FTRACE_DIRECT
 	select HAVE_SAMPLE_FTRACE_DIRECT_MULTI
 	select HAVE_STACKPROTECTOR
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 252d63942f34..adbc9023d7f0 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -34,6 +34,9 @@ ifeq ($(CONFIG_ARCH_RV64I),y)
 	KBUILD_AFLAGS += -mabi=lp64
 
 	KBUILD_LDFLAGS += -melf64lriscv
+
+	KBUILD_RUSTFLAGS += -Ctarget-cpu=generic-rv64 --target=riscv64imac-unknown-none-elf \
+			    -Cno-redzone
 else
 	BITS := 32
 	UTS_MACHINE := riscv32
@@ -68,6 +71,10 @@ riscv-march-$(CONFIG_FPU)		:= $(riscv-march-y)fd
 riscv-march-$(CONFIG_RISCV_ISA_C)	:= $(riscv-march-y)c
 riscv-march-$(CONFIG_RISCV_ISA_V)	:= $(riscv-march-y)v
 
+ifneq ($(CONFIG_RISCV_ISA_C),y)
+	KBUILD_RUSTFLAGS += -Ctarget-feature=-c
+endif
+
 ifdef CONFIG_TOOLCHAIN_NEEDS_OLD_ISA_SPEC
 KBUILD_CFLAGS += -Wa,-misa-spec=2.2
 KBUILD_AFLAGS += -Wa,-misa-spec=2.2
diff --git a/scripts/generate_rust_target.rs b/scripts/generate_rust_target.rs
index 54919cf48621..8f7846b9029a 100644
--- a/scripts/generate_rust_target.rs
+++ b/scripts/generate_rust_target.rs
@@ -150,6 +150,12 @@ fn main() {
     // `llvm-target`s are taken from `scripts/Makefile.clang`.
     if cfg.has("ARM64") {
         panic!("arm64 uses the builtin rustc aarch64-unknown-none target");
+    } else if cfg.has("RISCV") {
+        if cfg.has("64BIT") {
+            panic!("64-bit RISC-V uses the builtin rustc riscv64-unknown-none-elf target");
+        } else {
+            panic!("32-bit RISC-V is an unsupported architecture");
+        }
     } else if cfg.has("X86_64") {
         ts.push("arch", "x86_64");
         ts.push(
-- 
2.43.0

Re: [PATCH v3 1/1] RISC-V: enable building 64-bit kernels with rust support

[Gary Guo]

On Tue,  9 Apr 2024 18:25:16 +0100
Conor Dooley <conor@kernel.org> wrote:

> From: Miguel Ojeda <ojeda@kernel.org>
> 
> The rust modules work on 64-bit RISC-V, with no twiddling required.
> Select HAVE_RUST and provide the required flags to kbuild so that the
> modules can be used. The Makefile and Kconfig changes are lifted from
> work done by Miguel in the Rust-for-Linux tree, hence his authorship.
> Following the rabbit hole, the Makefile changes originated in a script,
> created based on config files originally added by Gary, hence his
> co-authorship.

Thanks for sending the patch!

> 32-bit is broken in core rust code, so support is limited to 64-bit:
> ld.lld: error: undefined symbol: __udivdi3

I wouldn't call the core rust code broken :)

The missing symbol here should be easily stubbed by changing the
redirect-intrinsics in rust/Makefile and adding a stub in
compiler_builtins.rs. Although we probably instead of panicking, want
to redirect the division to kernel division routine (IIRC the division
is used for formatting integers, which is a legit use of division).

> 
> As 64-bit RISC-V is now supported, add it to the arch support table.
> 
> Co-developed-by: Gary Guo <gary@garyguo.net>
> Signed-off-by: Gary Guo <gary@garyguo.net>
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
> Co-developed-by: Conor Dooley <conor.dooley@microchip.com>
> Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
> ---
>  Documentation/rust/arch-support.rst | 1 +
>  arch/riscv/Kconfig                  | 1 +
>  arch/riscv/Makefile                 | 7 +++++++
>  scripts/generate_rust_target.rs     | 6 ++++++
>  4 files changed, 15 insertions(+)

Re: [PATCH v3 0/1] RISC-V: enable rust

[Björn Töpel]

Conor Dooley <conor@kernel.org> writes:

> From: Conor Dooley <conor.dooley@microchip.com>
>
> I've intentionally not turned on the gcc support, as discussed on
> v1. I've also switched over to using the target, but it is a bit heavier
> than the one arm64 seems to be using. RISC-V has fewer targets available
> and this was the closest. I preserved the redzone disabling, just moved
> into the Makefile. Any comment from Gary or the LLVM lads on the target
> would be great I think:
> https://github.com/rust-lang/rust/blob/master/compiler/rustc_target/src/spec/targets/riscv64imac_unknown_none_elf.rs
> arm64 is using:
> https://github.com/rust-lang/rust/blob/master/compiler/rustc_target/src/spec/targets/aarch64_unknown_none.rs
>
> I was gonna send this yesterday, but found out last minute I had invalid
> code in the target generation script. The kernel test robot had given my
> branch the global all-clear - the rust coverage with all the
> "depends on !FOO" must really limit the build coverage. I built for x86
> with rust enabled locally this time to make sure..
>
> As this as lifted from the state of the Rust-for-Linux tree, the commit
> messages from there cannot be preserved, so these patches have commit
> messages that I wrote.
>
> I've tested this on Icicle, and the modules seem to work as expected.
> Unfortunately there appear to be implicit 32-bit divisions (or similar)
> in core Rust code, so, as in the downstream Rust-for-Linux tree, Rust is
> only enabled for 64-bit.

Nice, works with my simple test on VisionFive 2 as well! Cool to have
Rust support in! Now, BTF just needs to be supported, and I can have
Rust *and* BPF in my kernels! :-P \o/

Tested-by: Björn Töpel <bjorn@rivosinc.com>

Re: [PATCH v3 0/1] RISC-V: enable rust

[patchwork-bot+linux-riscv]

Hello:

This patch was applied to riscv/linux.git (for-next)
by Palmer Dabbelt <palmer@rivosinc.com>:

On Tue,  9 Apr 2024 18:25:15 +0100 you wrote:
> From: Conor Dooley <conor.dooley@microchip.com>
> 
> I've intentionally not turned on the gcc support, as discussed on
> v1. I've also switched over to using the target, but it is a bit heavier
> than the one arm64 seems to be using. RISC-V has fewer targets available
> and this was the closest. I preserved the redzone disabling, just moved
> into the Makefile. Any comment from Gary or the LLVM lads on the target
> would be great I think:
> https://github.com/rust-lang/rust/blob/master/compiler/rustc_target/src/spec/targets/riscv64imac_unknown_none_elf.rs
> arm64 is using:
> https://github.com/rust-lang/rust/blob/master/compiler/rustc_target/src/spec/targets/aarch64_unknown_none.rs
> 
> [...]

Here is the summary with links:
  - [v3,1/1] RISC-V: enable building 64-bit kernels with rust support
    https://git.kernel.org/riscv/c/81889e8523e6

You are awesome, thank you!
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