riscv: Use 64-bit variable for output in __get_user_asm

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[ Upstream commit bdce162f2e ]

After commit f6bff7827a ("riscv: uaccess: use 'asm_goto_output' for
get_user()"), which was the first commit that started using asm goto
with outputs on RISC-V, builds of clang built with assertions enabled
start crashing in certain files that use get_user() with:

  clang: llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp:12743: Register FollowCopyChain(MachineRegisterInfo &, Register): Assertion `MI->getOpcode() == TargetOpcode::COPY && "start of copy chain MUST be COPY"' failed.

Internally, LLVM generates an addiw instruction when the output of the
inline asm (which may be any scalar type) needs to be sign extended for
ABI reasons, such as a later function call, so that basic block does not
have to do it.

Use a temporary 64-bit variable as the output of the inline assembly in
__get_user_asm() and explicitly cast it to truncate it if necessary,
avoiding the addiw that triggers the assertion.

Link: https://github.com/ClangBuiltLinux/linux/issues/2092
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Link: https://patch.msgid.link/20260116-riscv-wa-llvm-asm-goto-outputs-assertion-failure-v3-1-55b5775f989b@kernel.org
Signed-off-by: Paul Walmsley <pjw@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

...

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Nathan Chancellor 2026-01-16 15:44:34 -07:00 • committed by Greg Kroah-Hartman

parent 4530f4e4d0

commit c65a1a72a4

1 changed files with 12 additions and 2 deletions

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arch/riscv/include/asm/uaccess.h

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