215baed16f
While looking at the disassembly for the epoll stuff I noticed that this
expands to quite a lot of code that the compiler can't optimize out for
LP64 (because it doesn't know that the "copy the argument into a local
and then use the local" bit isn't important).
There are two obvious options here. Something like this:
```
int signalfd64(int fd, const sigset64_t* mask, int flags) {
return __signalfd4(fd, mask, sizeof(*mask), flags);
}
int signalfd(int fd, const sigset_t* mask, int flags) {
#if defined(__LP64__)
return signalfd64(fd, mask, flags);
#else
SigSetConverter set = {.sigset = *mask};
return signalfd64(fd, &set.sigset64, flags);
#endif
}
```
Or something like this:
```
int signalfd64(int fd, const sigset64_t* mask, int flags) {
return __signalfd4(fd, mask, sizeof(*mask), flags);
}
#if defined(__LP64__)
__strong_alias(signalfd, signalfd64);
#else
int signalfd(int fd, const sigset_t* mask, int flags) {
SigSetConverter set = {};
set.sigset = *mask;
return signalfd64(fd, &set.sigset64, flags);
}
#endif
```
The former is slightly more verbose, but seems a bit more obvious, so I
initially went with that. (The former is more verbose in the generated
code too, given that the latter expands to _no_ code, just another symbol
pointing to the same code address.)
Having done that, I realized that slight changes to the interface would
let clang optimize away most/all of the overhead for LP64 with the only
preprocessor hackery being in SigSetConverter itself.
I also pulled out the legacy bsd `int` conversions since they're only
used in two (secret!) functions, so it's clearer to just have a separate
union for them. While doing so, I suppressed those functions for
riscv64, since there's no reason to keep carrying that mistake forward.
posix_spawn() is another simple case that doesn't actually benefit from
SigSetConverter, so I've given that its own anonymous union too.
Test: treehugger
Change-Id: Iaf67486da40d40fc53ec69717c3492ab7ab81ad6
72 lines
2.4 KiB
C++
72 lines
2.4 KiB
C++
/*
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* Copyright (C) 2018 The Android Open Source Project
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#pragma once
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// Android's 32-bit ABI shipped with a sigset_t too small to include any
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// of the realtime signals, so we have both sigset_t and sigset64_t. Many
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// new system calls only accept a sigset64_t, so this helps paper over
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// the difference at zero cost to LP64 in most cases after the optimizer
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// removes the unnecessary temporary `ptr`.
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struct SigSetConverter {
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public:
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SigSetConverter(const sigset_t* s) : SigSetConverter(const_cast<sigset_t*>(s)) {}
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SigSetConverter(sigset_t* s) {
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#if defined(__LP64__)
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// sigset_t == sigset64_t on LP64.
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ptr = s;
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#else
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sigset64 = {};
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if (s != nullptr) {
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original_ptr = s;
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sigset = *s;
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ptr = &sigset64;
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} else {
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ptr = nullptr;
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}
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#endif
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}
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void copy_out() {
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#if defined(__LP64__)
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// We used the original pointer directly, so no copy needed.
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#else
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*original_ptr = sigset;
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#endif
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}
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sigset64_t* ptr;
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private:
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[[maybe_unused]] sigset_t* original_ptr;
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union {
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sigset_t sigset;
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sigset64_t sigset64;
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};
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};
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