linux-kernel - [RFC RESEND 2/2] RISC-V: enable building the 64-bit kernels with rust support

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Date:   Fri, 24 Feb 2023 13:50:44 +0000
From:   Conor Dooley <conor.dooley@...rochip.com>
To:     <linux-riscv@...ts.infradead.org>
CC:     Conor Dooley <conor.dooley@...rochip.com>, <conor@...nel.org>,
        "Miguel Ojeda" <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        "Wedson Almeida Filho" <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Jonathan Corbet <corbet@....net>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        "Nathan Chancellor" <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, <rust-for-linux@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <llvm@...ts.linux.dev>
Subject: [RFC RESEND 2/2] RISC-V: enable building the 64-bit kernels with rust support

From: Miguel Ojeda <ojeda@...nel.org>

The rust modules work on 64-bit RISC-V, with no twiddling required.
Select HAS_RUST and provide the required flags to kbuild so that the
modules can be used.
32-bit is broken in core rust code, so support is limited to 64-bit
only: ld.lld: error: undefined symbol: __udivdi3

Signed-off-by: Miguel Ojeda <ojeda@...nel.org>
Signed-off-by: Conor Dooley <conor.dooley@...rochip.com>
---
 Documentation/rust/arch-support.rst | 2 ++
 arch/riscv/Kconfig                  | 1 +
 arch/riscv/Makefile                 | 3 ++-
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/Documentation/rust/arch-support.rst b/Documentation/rust/arch-support.rst
index 6982b63775da..197919158596 100644
--- a/Documentation/rust/arch-support.rst
+++ b/Documentation/rust/arch-support.rst
@@ -15,5 +15,7 @@ support corresponds to ``S`` values in the ``MAINTAINERS`` file.
 ============  ================  ==============================================
 Architecture  Level of support  Constraints
 ============  ================  ==============================================
+``riscv``     Maintained        ``rv64`` only.
+============  ================  ==============================================
 ``x86``       Maintained        ``x86_64`` only.
 ============  ================  ==============================================
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 81eb031887d2..73174157212d 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -115,6 +115,7 @@ config RISCV
 	select HAVE_POSIX_CPU_TIMERS_TASK_WORK
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_RSEQ
+	select HAVE_RUST if 64BIT
 	select HAVE_STACKPROTECTOR
 	select HAVE_SYSCALL_TRACEPOINTS
 	select IRQ_DOMAIN
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 76989561566b..0d6fc4e25221 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -29,8 +29,8 @@ ifeq ($(CONFIG_ARCH_RV64I),y)
 
 	KBUILD_CFLAGS += -mabi=lp64
 	KBUILD_AFLAGS += -mabi=lp64
-
 	KBUILD_LDFLAGS += -melf64lriscv
+	KBUILD_RUSTFLAGS += -Ctarget-cpu=generic-rv64
 else
 	BITS := 32
 	UTS_MACHINE := riscv32
@@ -38,6 +38,7 @@ else
 	KBUILD_CFLAGS += -mabi=ilp32
 	KBUILD_AFLAGS += -mabi=ilp32
 	KBUILD_LDFLAGS += -melf32lriscv
+	KBUILD_RUSTFLAGS += -Ctarget-cpu=generic-rv32
 endif
 
 ifeq ($(CONFIG_LD_IS_LLD),y)
-- 
2.39.2