Fix epilogue codegen to avoid leaving the stack pointer in an invalid
state. Previously Thumb2 would restore sp from fp like this:
mov sp, r7
sub, sp, #4
If an interrupt is taken after the 'mov' but before the 'sub', callee-saved
registers might be clobbered by the interrupt handler. Instead, try
restoring directly from sp:
add sp, #4
Or, if necessary (with VLA, etc.) use a scratch register to compute sp and
then restore it:
sub.w r4, r7, #8
mov sp, r7
rdar://8465407
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119977 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/ARM/ARMFrameInfo.cpp b/lib/Target/ARM/ARMFrameInfo.cpp
index 7766b1f..62f3f98 100644
--- a/lib/Target/ARM/ARMFrameInfo.cpp
+++ b/lib/Target/ARM/ARMFrameInfo.cpp
@@ -17,6 +17,7 @@
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Target/TargetOptions.h"
using namespace llvm;
@@ -212,15 +213,21 @@
if (NumBytes) {
// Adjust SP after all the callee-save spills.
emitSPUpdate(isARM, MBB, MBBI, dl, TII, -NumBytes);
- if (HasFP)
+ if (HasFP && isARM)
+ // Restore from fp only in ARM mode: e.g. sub sp, r7, #24
+ // Note it's not safe to do this in Thumb2 mode because it would have
+ // taken two instructions:
+ // mov sp, r7
+ // sub sp, #24
+ // If an interrupt is taken between the two instructions, then sp is in
+ // an inconsistent state (pointing to the middle of callee-saved area).
+ // The interrupt handler can end up clobbering the registers.
AFI->setShouldRestoreSPFromFP(true);
}
- if (STI.isTargetELF() && hasFP(MF)) {
+ if (STI.isTargetELF() && hasFP(MF))
MFI->setOffsetAdjustment(MFI->getOffsetAdjustment() -
AFI->getFramePtrSpillOffset());
- AFI->setShouldRestoreSPFromFP(true);
- }
AFI->setGPRCalleeSavedArea1Size(GPRCS1Size);
AFI->setGPRCalleeSavedArea2Size(GPRCS2Size);
@@ -275,7 +282,7 @@
// If the frame has variable sized objects then the epilogue must restore
// the sp from fp.
- if (!AFI->shouldRestoreSPFromFP() && MFI->hasVarSizedObjects())
+ if (MFI->hasVarSizedObjects())
AFI->setShouldRestoreSPFromFP(true);
}
@@ -326,9 +333,21 @@
if (isARM)
emitARMRegPlusImmediate(MBB, MBBI, dl, ARM::SP, FramePtr, -NumBytes,
ARMCC::AL, 0, TII);
- else
- emitT2RegPlusImmediate(MBB, MBBI, dl, ARM::SP, FramePtr, -NumBytes,
+ else {
+ // It's not possible to restore SP from FP in a single instruction.
+ // For Darwin, this looks like:
+ // mov sp, r7
+ // sub sp, #24
+ // This is bad, if an interrupt is taken after the mov, sp is in an
+ // inconsistent state.
+ // Use the first callee-saved register as a scratch register.
+ assert(MF.getRegInfo().isPhysRegUsed(ARM::R4) &&
+ "No scratch register to restore SP from FP!");
+ emitT2RegPlusImmediate(MBB, MBBI, dl, ARM::R4, FramePtr, -NumBytes,
ARMCC::AL, 0, TII);
+ BuildMI(MBB, MBBI, dl, TII.get(ARM::tMOVgpr2gpr), ARM::SP)
+ .addReg(ARM::R4);
+ }
} else {
// Thumb2 or ARM.
if (isARM)