Re: [PATCH] rust: Add PowerPC support

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:

quoted

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!

quoted

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

quoted

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.

quoted

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