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[libunwind] Call __arm_za_disable before entering EH #160905

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[libunwind] Call __arm_za_disable before entering EH #160905

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33dc84e
[libunwind] Call `__arm_za_disable` before entering EH
MacDue Sep 26, 2025
962dfe9
Fixups
MacDue Sep 26, 2025
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27 changes: 27 additions & 0 deletions libunwind/src/UnwindLevel1.c
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Original file line number Diff line number Diff line change
Expand Up @@ -186,6 +186,10 @@ unwind_phase1(unw_context_t *uc, unw_cursor_t *cursor, _Unwind_Exception *except
}
extern int __unw_step_stage2(unw_cursor_t *);

#if defined(__aarch64__)
extern void __attribute__((weak)) __arm_za_disable(void);
#endif

#if defined(_LIBUNWIND_USE_GCS)
// Enable the GCS target feature to permit gcspop instructions to be used.
__attribute__((target("+gcs")))
Expand All @@ -198,6 +202,29 @@ unwind_phase2(unw_context_t *uc, unw_cursor_t *cursor,
_LIBUNWIND_TRACE_UNWINDING("unwind_phase2(ex_obj=%p)",
(void *)exception_object);

#if defined(__aarch64__)
// The platform must ensure that all the following conditions are true on
// entry to EH:
//
// - PSTATE.SM is 0.
// - PSTATE.ZA is 0.
// - TPIDR2_EL0 is null.
//
// The first point is ensured by routines for throwing exceptions having a
// non-streaming interface. TPIDR2_EL0 is set to null and ZA disabled by
// calling __arm_za_disable.
//
// See:
// https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst#exceptions
if (__arm_za_disable) {
__arm_za_disable();
} else {
// FIXME: If SME is available and `__arm_za_disable` is not, this should
// abort.
_LIBUNWIND_DEBUG_LOG("failed to call __arm_za_disable in %s", __FUNCTION__);
}
#endif

// uc is initialized by __unw_getcontext in the parent frame. The first stack
// frame walked is unwind_phase2.
unsigned framesWalked = 1;
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