mirror of
https://github.com/jart/cosmopolitan.git
synced 2025-01-31 19:43:32 +00:00
6f7d0cb1c3
This makes breaking changes to add underscores to many non-standard function names provided by the c library. MODE=tiny is now tinier and we now use smaller locks that are better for tiny apps in this mode. Some headers have been renamed to be in the same folder as the build package, so it'll be easier to know which build dependency is needed. Certain old misguided interfaces have been removed. Intel intrinsics headers are now listed in libc/isystem (but not in the amalgamation) to help further improve open source compatibility. Header complexity has also been reduced. Lastly, more shell scripts are now available.
63 lines
3.3 KiB
C
63 lines
3.3 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
|
|
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
|
|
╞══════════════════════════════════════════════════════════════════════════════╡
|
|
│ Copyright 2022 Justine Alexandra Roberts Tunney │
|
|
│ │
|
|
│ Permission to use, copy, modify, and/or distribute this software for │
|
|
│ any purpose with or without fee is hereby granted, provided that the │
|
|
│ above copyright notice and this permission notice appear in all copies. │
|
|
│ │
|
|
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
|
|
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
|
|
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
|
|
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
|
|
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
|
|
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
|
|
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
|
|
│ PERFORMANCE OF THIS SOFTWARE. │
|
|
╚─────────────────────────────────────────────────────────────────────────────*/
|
|
#include "libc/dce.h"
|
|
#include "libc/errno.h"
|
|
#include "libc/intrin/fsgsbase.h"
|
|
#include "libc/nexgen32e/x86feature.h"
|
|
|
|
/**
|
|
* Returns true if FSGSBASE ISA can be used.
|
|
*
|
|
* If this function returns true (Linux 5.9+ or FreeBSD) then you should
|
|
* be able to read/write to the %gs / %fs x86 segment registers in about
|
|
* one or two clock cycles which gives you a free addition operation for
|
|
* all assembly ops that reference memory.
|
|
*
|
|
* The FSGSBASE ISA was introduced by Intel with Ivybridge (c. 2012) but
|
|
* the Linux Kernel didn't authorize us to use it until 2020, once Intel
|
|
* had to start backdooring customer kernels so that they could have it.
|
|
* AMD introduced support for the FSGSBASE ISA in Excavator, aka bdver4.
|
|
*
|
|
* @return boolean indicating if feature can be used
|
|
* @see _rdfsbase()
|
|
* @see _rdgsbase()
|
|
* @see _wrfsbase()
|
|
* @see _wrgsbase()
|
|
*/
|
|
privileged int _have_fsgsbase(void) {
|
|
// Linux 5.9 (c. 2020) introduced close_range() and fsgsbase support.
|
|
// it's cheaper to test for close_range() than handle an op crashing.
|
|
// Windows lets us use these instructions but they don't really work.
|
|
int ax;
|
|
if (X86_HAVE(FSGSBASE)) {
|
|
if (IsLinux()) {
|
|
asm volatile("syscall"
|
|
: "=a"(ax)
|
|
: "0"(436 /* close_range */), "D"(-1), "S"(-2), "d"(0)
|
|
: "rcx", "r11", "memory");
|
|
return ax == -22; // EINVAL
|
|
} else if (IsFreebsd()) {
|
|
return 1;
|
|
} else {
|
|
return 0;
|
|
}
|
|
} else {
|
|
return 0;
|
|
}
|
|
}
|