tnfchris added inline comments.
================
Comment at: clang/lib/Driver/ToolChains/Clang.cpp:3460
+ } else if (EffectiveTriple.isArm() || EffectiveTriple.isThumb()) {
+ CmdArgs.push_back("-mstack-probe-size=1024");
+ }
----------------
efriedma wrote:
> tnfchris wrote:
> > efriedma wrote:
> > > Why 1024?
> > 1024 was experimentally determined by Arm and is part of the ABI for stack
> > clash (which has not yet been published). It was determined by examining a
> > large number of programs and looking at the function stack usages. 1024
> > covers 80-90% of programs such that we can minimize the number of probes
> > required in the average cases.
> There are actually multiple numbers involved here, no? One is the spacing of
> probes, i.e. if allocating a large amount of stack, how many times you need
> to probe; this is basically the page size of the target. the other is how
> much unprobed space a function is allowed to allocate before calling another
> function. Referring to the the AArch64 patch, -mstack-probe-size is the
> former, the hardcoded "1024" is the latter.
I hadn't looked at the patch in detail yet, I thought this was the probing
offset. But you're right, what I thought of was `StackClashCallerGuard`, if
`stack-probe-size` indeed the guard size itself, then yeah this would be wrong.
It seems incorrect to allow it smaller than the page size.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D154911/new/
https://reviews.llvm.org/D154911
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