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JIT: Switch GS cookie check temp reg to use r10 for tailcalls #120941

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Merged
merged 1 commit into from
Oct 22, 2025
Merged

JIT: Switch GS cookie check temp reg to use r10 for tailcalls #120941

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13 changes: 6 additions & 7 deletions src/coreclr/jit/codegencommon.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2519,17 +2519,17 @@ CorInfoHelpFunc CodeGenInterface::genWriteBarrierHelperForWriteBarrierForm(GCInf
//
regMaskTP CodeGenInterface::genGetGSCookieTempRegs(bool tailCall)
{
#ifdef TARGET_XARCH
#ifdef TARGET_AMD64
if (tailCall)
{
// If we are tailcalling then return registers are available for use
return RBM_RAX;
// If we are tailcalling then arg regs cannot be used. For both SysV and winx64 that
// leaves rax, r10, r11. rax and r11 are used for indirection cells, so we pick r10.
return RBM_R10;
}

#ifdef TARGET_AMD64
// Otherwise on x64 (win-x64 and SysV) r8 is never used for return values
return RBM_R8;
#else
#elif TARGET_X86
assert(!tailCall);
// On x86 it's more difficult: we have only eax, ecx and edx available as volatile
// registers, and all of them may be used for return values (longs + async continuation).
if (compiler->compIsAsync())
Expand All @@ -2540,7 +2540,6 @@ regMaskTP CodeGenInterface::genGetGSCookieTempRegs(bool tailCall)

// Outside async ecx is not used for returns.
return RBM_ECX;
#endif
#else
return RBM_GSCOOKIE_TMP;
#endif
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5 changes: 5 additions & 0 deletions src/coreclr/jit/morph.cpp
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Expand Up @@ -1773,6 +1773,11 @@ void CallArgs::AddFinalArgsAndDetermineABIInfo(Compiler* comp, GenTreeCall* call
InsertAfterThisOrFirst(comp, NewCallArg::Primitive(arg).WellKnown(WellKnownArg::PInvokeCookie));
// put destination into R10/EAX
arg = comp->gtClone(call->gtCallAddr, true);
// On x64 the pinvoke target is passed in r11 which is the same
// register as the gs cookie check may use. That would be a problem if
// this was a tailcall, but we do not tailcall functions with
// non-standard added args except indirection cells currently.
assert(!call->IsFastTailCall());
InsertAfterThisOrFirst(comp, NewCallArg::Primitive(arg).WellKnown(WellKnownArg::PInvokeTarget));

// finally change this call to a helper call
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