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Fix up hijacking on arm32 (preserve async continuation register) #123057

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Merged
eduardo-vp merged 7 commits into from
Jan 13, 2026
Merged

Fix up hijacking on arm32 (preserve async continuation register) #123057

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fbc5b68
Fix up hijacking on arm32
Jan 10, 2026
4a7bd6b
Fix whitespace
Jan 10, 2026
19327f9
PR feedback
Jan 12, 2026
5028701
Update src/coreclr/nativeaot/Runtime/arm/GcProbe.S
eduardo-vp Jan 12, 2026
99a3893
Use r12 instead of r3
Jan 12, 2026
c2eb1ec
Nit
Jan 12, 2026
80c9a8d
Apply suggestions from code review
jkotas Jan 13, 2026
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37 changes: 26 additions & 11 deletions src/coreclr/nativeaot/Runtime/arm/GcProbe.S
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,7 @@
// incoming register values into it.
PROLOG_VPUSH "{d0-d3}" // Save d0-d3 which can have the floating point return value
PROLOG_PUSH "{r0,r1}" // Save return registers
PROLOG_PUSH "{r2}" // Save r2, it might contain an objectref (async continuation)
PROLOG_STACK_ALLOC 4 // Space for caller's SP
PROLOG_PUSH "{r4-r10}" // Save non-volatile registers
PROLOG_STACK_ALLOC 8 // Space for flags and Thread*
Expand All @@ -32,7 +33,7 @@
str \trashReg, [sp, #OFFSETOF__PInvokeTransitionFrame__m_Flags]

// Compute SP value at entry to this method and save it in slot of the frame.
add \trashReg, sp, #(14 * 4 + 4 * 8)
add \trashReg, sp, #(15 * 4 + 4 * 8)
str \trashReg, [sp, #(11 * 4)]

// Link the frame into the Thread
Expand All @@ -49,6 +50,7 @@
EPILOG_STACK_FREE 8 // Discard flags and Thread*
EPILOG_POP "{r4-r10}" // Restore non-volatile registers
EPILOG_STACK_FREE 4 // Discard caller's SP
EPILOG_POP "{r2}" // Restore r2
EPILOG_POP "{r0,r1}" // Restore return registers
EPILOG_VPOP "{d0-d3}" // Restore d0-d3 which can have the floating point return value
.endm
Expand All @@ -61,25 +63,34 @@
// All registers correct for return to the original return address.
//
// Register state on exit:
// r2: thread pointer
// r3: trashed
// r3: thread pointer
// r0, r1, r2: preserved, other volatile regs trashed
//
.macro FixupHijackedCallstack
push {r0, r1}
push {r0, r1, r2}

// align stack to 8 bytes
sub sp, sp, #4

// r0 <- GetThread()
INLINE_GETTHREAD

mov r2, r0
pop {r0, r1}
mov r3, r0

// restore alignment
add sp, sp, #4

pop {r0, r1, r2}

// Fix the stack by restoring the original return address
ldr lr, [r2, #OFFSETOF__Thread__m_pvHijackedReturnAddress]
ldr lr, [r3, #OFFSETOF__Thread__m_pvHijackedReturnAddress]

// Clear hijack state
mov r3, #0
str r3, [r2, #OFFSETOF__Thread__m_ppvHijackedReturnAddressLocation]
str r3, [r2, #OFFSETOF__Thread__m_pvHijackedReturnAddress]
push {r0}
mov r0, #0
str r0, [r3, #OFFSETOF__Thread__m_ppvHijackedReturnAddressLocation]
str r0, [r3, #OFFSETOF__Thread__m_pvHijackedReturnAddress]
pop {r0}
.endm

NESTED_ENTRY RhpWaitForGC, _TEXT, NoHandler
Expand Down Expand Up @@ -110,12 +121,16 @@ NESTED_END RhpGcPollRare
NESTED_ENTRY RhpGcProbeHijack, _TEXT, NoHandler
FixupHijackedCallstack

// r3 has the thread pointer
push {r3}
PREPARE_EXTERNAL_VAR_INDIRECT RhpTrapThreads, r3
tst r3, #TrapThreadsFlags_TrapThreads
pop {r3}
bne LOCAL_LABEL(WaitForGC)
bx lr
LOCAL_LABEL(WaitForGC):
mov r12, #(DEFAULT_FRAME_SAVE_FLAGS + PTFF_SAVE_R0)
mov r2, r3 // Move thread pointer to r2 for RhpWaitForGC
mov r12, #(DEFAULT_FRAME_SAVE_FLAGS + PTFF_SAVE_R0 + PTFF_SAVE_R2)
orr r12, r12, #PTFF_THREAD_HIJACK
b RhpWaitForGC
NESTED_END RhpGcProbeHijack
Expand Down
2 changes: 2 additions & 0 deletions src/coreclr/nativeaot/Runtime/unix/unixasmmacrosarm.inc
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Original file line number Diff line number Diff line change
Expand Up @@ -9,10 +9,12 @@
#define TSF_SuppressGcStress 0x08
#define TSF_DoNotTriggerGc 0x10

// These must match the PInvokeTransitionFrameFlags enum
#define PTFF_SAVE_ALL_PRESERVED 0x0000007F // NOTE: R11 is not included in this set!
#define PTFF_SAVE_R9 0x00000020
#define PTFF_SAVE_SP 0x00000100
#define PTFF_SAVE_R0 0x00000200
#define PTFF_SAVE_R2 0x00000800
#define PTFF_THREAD_HIJACK 0x00004000 // indicates that this is a frame for a hijacked call

#define DEFAULT_FRAME_SAVE_FLAGS (PTFF_SAVE_ALL_PRESERVED + PTFF_SAVE_SP)
Expand Down