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8369190: JavaFrameAnchor on AArch64 has unnecessary barriers and wrong store order in MacroAssembler #27645

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8369190: JavaFrameAnchor on AArch64 has unnecessary barriers and wrong store order in MacroAssembler #27645

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462c63e
JDK-8369190: JavaFrameAnchor on AArch64 appears to be missing barriers
jcking Oct 6, 2025
a0058eb
Update comments
jcking Oct 6, 2025
a141449
Rename ACGT -> AGCT
jcking Oct 6, 2025
253417f
Remove barriers and just fix program order for sp store in MacroAssem…
jcking Oct 6, 2025
016769d
Add comment to JavaFrameAnchor regarding no need for fencing
jcking Oct 6, 2025
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7 changes: 5 additions & 2 deletions src/hotspot/cpu/aarch64/javaFrameAnchor_aarch64.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -39,9 +39,11 @@
// 3 - restoring an old state (javaCalls)

void clear(void) {
// No fencing required, the members are declared volatile so the compiler will not reorder and
// the profiler always reads from the same thread and should observe the state in program order.

// clearing _last_Java_sp must be first
_last_Java_sp = nullptr;
OrderAccess::release();
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You still need a compiler fence here.

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Maybe not, if this is the same thread as readers. I don't know what it's for.

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OrderAccess::release() is more than a compiler barrier on AArch64. I am guessing this was copied from x86 or one of the others where that same function is a compiler barrier? Should I move compiler_barrier from the random source files its in, into globalDefinitions, and use that?

_last_Java_fp = nullptr;
_last_Java_pc = nullptr;
}
Expand All @@ -54,9 +56,10 @@
// To act like previous version (pd_cache_state) don't null _last_Java_sp
// unless the value is changing
//
// No fencing required, the members are declared volatile so the compiler will not reorder and
// the profiler always reads from the same thread and should observe the state in program order.
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@dean-long dean-long Oct 7, 2025 •
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I don't think copy() is ever called. Can we remove it?

if (_last_Java_sp != src->_last_Java_sp) {
_last_Java_sp = nullptr;
OrderAccess::release();
}
_last_Java_fp = src->_last_Java_fp;
_last_Java_pc = src->_last_Java_pc;
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5 changes: 3 additions & 2 deletions src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp
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Expand Up @@ -634,12 +634,13 @@ void MacroAssembler::set_last_Java_frame(Register last_java_sp,
last_java_sp = esp;
}

str(last_java_sp, Address(rthread, JavaThread::last_Java_sp_offset()));

// last_java_fp is optional
if (last_java_fp->is_valid()) {
str(last_java_fp, Address(rthread, JavaThread::last_Java_fp_offset()));
}

// Must be last so profiler will always see valid frame if has_last_frame() is true
str(last_java_sp, Address(rthread, JavaThread::last_Java_sp_offset()));
}

void MacroAssembler::set_last_Java_frame(Register last_java_sp,
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