From: FUJITA Tomonori <tomo@flapping.org>
To: anton.ivanov@cambridgegreys.com, johannes@sipsolutions.net,
ojeda@kernel.org, richard@nod.at
Cc: a.hindborg@kernel.org, acourbot@nvidia.com, aliceryhl@google.com,
bjorn3_gh@protonmail.com, boqun@kernel.org, dakr@kernel.org,
daniel.almeida@collabora.com, david@davidgow.net,
gary@garyguo.net, linux-um@lists.infradead.org,
lossin@kernel.org, tamird@kernel.org, tmgross@umich.edu,
work@onurozkan.dev, rust-for-linux@vger.kernel.org,
FUJITA Tomonori <fujita.tomonori@gmail.com>
Subject: [PATCH v1] rust: arch/um: Fix loading Rust modules
Date: Sun, 4 Oct 2026 21:12:30 +0900 [thread overview]
Message-ID: <20261004121230.373216-1-tomo@flapping.org> (raw)
From: FUJITA Tomonori <fujita.tomonori@gmail.com>
Rust modules fail to load on x86_64 UML:
# insmod rnull_mod.ko
subarch: rnull_mod: Unknown rela relocation: 9
insmod: can't insert 'rnull_mod.ko': invalid module format
arch/um/Makefile adds -Crelocation-model=pie to KBUILD_RUSTFLAGS. This
comes after -Crelocation-model=static in the top-level Makefile, so all
Rust code on UML, both built-in code and modules, is built as PIE. In
PIE mode, rustc accesses statics in other crates through the GOT and
emits R_X86_64_GOTPCREL (9) relocations. UML uses the x86 module loader,
and it does not handle them.
Remove the flag. Rust code, both built-in code and modules, then uses
the static relocation model, the same as C code.
Modules still fail to load with a larger mem=, such as mem=512M,
because Rust code uses the small code model while C code uses
-mcmodel=large. This is a separate problem.
Tested with clang 20 and rustc 1.90: vmlinux builds and boots, and
rnull_mod.ko loads with mem=32M.
Reported-by: Zigit Zo <zig@iorw.io>
Link: https://lore.kernel.org/rust-for-linux/62F5EEA0B866E9E0+20240903130606.292935-1-zig@iorw.io/
Assisted-by: LLM
Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
---
arch/um/Makefile | 2 --
1 file changed, 2 deletions(-)
diff --git a/arch/um/Makefile b/arch/um/Makefile
index 937639edc295..c4a99073f014 100644
--- a/arch/um/Makefile
+++ b/arch/um/Makefile
@@ -62,8 +62,6 @@ KBUILD_CFLAGS += $(CFLAGS) $(CFLAGS-y) -D__arch_um__ \
-Din6addr_any=kernel_in6addr_any -Dstrrchr=kernel_strrchr \
-D__close_range=kernel__close_range
-KBUILD_RUSTFLAGS += -Crelocation-model=pie
-
KBUILD_AFLAGS += $(ARCH_INCLUDE)
USER_CFLAGS = $(patsubst $(KERNEL_DEFINES),,$(patsubst -I%,,$(KBUILD_CFLAGS))) \
base-commit: 2dee3d3adcadcc57d62ba6608cd02f50b0c10264
--
2.43.0
reply other threads:[~2026-10-04 12:13 UTC|newest]
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