Re: [PATCH] rust: Add PowerPC support

Gary Guo
2026-02-04T12:36:43Z

On Wed Feb 4, 2026 at 10:41 AM GMT, Alice Ryhl wrote:
> On Wed, Feb 04, 2026 at 04:05:04AM +0100, Link Mauve wrote:
>> For now only Big Endian 32-bit PowerPC is supported, as that is the only
>> hardware I have. This has been tested on the Nintendo Wii so far, but I
>> plan on also using it on the GameCube, Wii U and Apple G4.
>
> Super cool!
>
>> These changes aren’t the only ones required to get the kernel to compile
>> and link on PowerPC, libcore will also have to be changed to not use
>> integer division to format u64, u128 and core::time::Duration, otherwise
>> __udivdi3() and __umoddi3() will have to be added. I have tested this
>> change by replacing the three implementations with unimplemented!() and
>> it linked just fine.
>
> Uh oh this seems tricky. How is this not a problem on arm32 too?
>
> Perhaps we should just be providing __udivdi3() and __umoddi3() in
> general?

I think there is some concern that if this is provided, then C side that uses
the divide operator instead of dividing function doesn't get linker error
anymore.

However, a proper way is to do this via the hooks that we already have in
`compiler_builtins.rs`.

This can either be replace these with panics or actual implementation, but for
libcore.o only.

Best,
Gary

>
>> diff --git a/arch/powerpc/include/asm/jump_label.h b/arch/powerpc/include/asm/jump_label.h
>> index d4eaba459a0e..238f0f625a36 100644
>> --- a/arch/powerpc/include/asm/jump_label.h
>> +++ b/arch/powerpc/include/asm/jump_label.h
>> @@ -15,14 +15,18 @@
>> #define JUMP_ENTRY_TYPE stringify_in_c(FTR_ENTRY_LONG)
>> #define JUMP_LABEL_NOP_SIZE 4
>>
>> +/* This macro is also expanded on the Rust side. */
>> +#define ARCH_STATIC_BRANCH_ASM(key, label) \
>> + "1:\n\t" \
>> + "nop # arch_static_branch\n\t" \
>> + ".pushsection __jump_table, \"aw\"\n\t" \
>> + ".long 1b - ., " label " - .\n\t" \
>> + JUMP_ENTRY_TYPE key " - .\n\t" \
>> + ".popsection \n\t"
>> +
>> static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
>> {
>> - asm goto("1:\n\t"
>> - "nop # arch_static_branch\n\t"
>> - ".pushsection __jump_table, \"aw\"\n\t"
>> - ".long 1b - ., %l[l_yes] - .\n\t"
>> - JUMP_ENTRY_TYPE "%c0 - .\n\t"
>> - ".popsection \n\t"
>> + asm goto(ARCH_STATIC_BRANCH_ASM("%c0", "%l[l_yes]")
>> : : "i" (&((char *)key)[branch]) : : l_yes);
>
> In case this patch takes a long time to land, it may make sense to split
> this part out in a separate patch that can land now.
>
> Also, consider pre-emptively updating arch_static_branch_jump too. We
> probably need it at some point in the future.
>
>> diff --git a/scripts/generate_rust_target.rs b/scripts/generate_rust_target.rs
>> index 38b3416bb979..0054880ba0ea 100644
>> --- a/scripts/generate_rust_target.rs
>> +++ b/scripts/generate_rust_target.rs
>> @@ -188,6 +188,16 @@ fn main() {
>> panic!("arm uses the builtin rustc target");
>> } else if cfg.has("ARM64") {
>> panic!("arm64 uses the builtin rustc aarch64-unknown-none target");
>> + } else if cfg.has("PPC32") {
>> + ts.push("arch", "powerpc");
>> + ts.push("data-layout", "E-m:e-p:32:32-Fn32-i64:64-n32");
>> + ts.push("features", "+soft-float");
>> + ts.push("llvm-target", "powerpc-unknown-eabi");
>> + if cfg.rustc_version_atleast(1, 91, 0) {
>> + ts.push("target-pointer-width", 32);
>> + } else {
>> + ts.push("target-pointer-width", "32");
>> + }
>
> Is there no built-in target we can use? I think we want to avoid adding
> new targets if at all possible.
>
> Alice