Re: [PATCH v2] random: vDSO: Avoid call to memset() when zeroing reserved in __cvdso_getrandom_data()

[Jason A. Donenfeld]

On Fri, Oct 02, 2026 at 11:49:32AM +0200, Nathan Chancellor wrote:
> On Thu, Oct 01, 2026 at 01:03:10PM +0200, Nathan Chancellor wrote:
> > On Thu, Oct 01, 2026 at 12:48:10PM +0200, Jason A. Donenfeld wrote:
> > > Does this commit seem okay with you? I used the diff you sent below and
> > > adjusted the commit message: https://git.zx2c4.com/linux-rng/commit/?id=56ff95ee85715047eb5b5220243778af657778c8
> > 
> > Yeah, that seems fine to me, thanks for taking care of it!
> 
> Can you adjust the LLVM value by one from 4294967295 to 4294967294? ~0U
> is actually a special value, so we hit an assertion in the SystemZ
> backend.
> 
>   https://github.com/llvm/llvm-project/blob/3f48e22a1f321d5d3341bd812803694cea588785/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp#L9547
>   https://github.com/llvm/llvm-project/blob/3f48e22a1f321d5d3341bd812803694cea588785/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp#L1470-L1471
> 
> clang: llvm/lib/Target/SystemZ/SystemZISelLowering.cpp:1471: virtual bool llvm::SystemZTargetLowering::findOptimalMemOpLowering(LLVMContext &, std::vector<EVT> &, unsigned int, const MemOp &, unsigned int, unsigned int, const AttributeList &, EVT *) const: Assertion `Limit != ~0U && "Expected EmitTargetCodeForMemXXX() to handle AlwaysInline cases."' failed.
> PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace and dumped files.
> Stack dump:
> 0.      Program arguments: ...
> 1.      <eof> parser at end of file
> 2.      Code generation
> 3.      Running pass 'Function Pass Manager' on module 'arch/s390/kernel/vdso/vgetrandom.c'.
> 4.      Running pass 'SystemZ DAG->DAG Pattern Instruction Selection' on function '@__kernel_getrandom'
> ...

Holy smokes. Sure, fixed:  https://git.zx2c4.com/linux-rng/commit/?id=eb13a1ff271b0d180687eebb30611b0b276d5193