Implement aarch64_get_thread_helper() for Windows AArch64#67
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raneashay wants to merge 1 commit intomicrosoft:mainfrom
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Implement aarch64_get_thread_helper() for Windows AArch64#67raneashay wants to merge 1 commit intomicrosoft:mainfrom
aarch64_get_thread_helper() for Windows AArch64#67raneashay wants to merge 1 commit intomicrosoft:mainfrom
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Prior to this patch, on Windows/AArch64, `aarch64_get_thread_helper()` resolves to `Thread::current()`, which, although correct, is suboptimal, since it requires all registers from `r0` through `r17` to be saved by the caller. Linux/AArch64 has a hand-written assembly implementation that clobbers just `x0` and `x1`, making it more efficient. This patch implements a similar hand-written assembly implementation for Windows. Unlike Linux, which stores the thread identifying information pointer in the `tpidr_el0` register, Windows stores the pointer to the Thread Environment Block in `x18`, so this assembly code basically reads the `*[*(x18 + 0x58) + _tls_index * 8] + _jvm_thr_current_tls_offset` address, where `0x58` is the offset into the TEB to get to the thread local storage pointer (see https://www.geoffchappell.com/studies/windows/km/ntoskrnl/inc/api/pebteb/teb/index.htm), and `_jvm_thr_current_tls_offset` is computed in `cache_global_variables()` once using `Thread::_thr_current` and is then reused in each call to the assembly code.
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Prior to this patch, on Windows/AArch64,
aarch64_get_thread_helper()resolves to
Thread::current(), which, although correct, is suboptimal,since it requires all registers from
r0throughr17to be saved bythe caller. Linux/AArch64 has a hand-written assembly implementation
that clobbers just
x0andx1, making it more efficient. This patchimplements a similar hand-written assembly implementation for Windows.
Unlike Linux, which stores the thread identifying information pointer in
the
tpidr_el0register, Windows stores the pointer to the ThreadEnvironment Block in
x18, so this assembly code basically reads the*[*(x18 + 0x58) + _tls_index * 8] + _jvm_thr_current_tls_offsetaddress, where
0x58is the offset into the TEB to get to the threadlocal storage pointer (see
https://www.geoffchappell.com/studies/windows/km/ntoskrnl/inc/api/pebteb/teb/index.htm),
and
_jvm_thr_current_tls_offsetis computed incache_global_variables()once usingThread::_thr_currentand is thenreused in each call to the assembly code.