mirror of
https://github.com/jart/cosmopolitan.git
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116 lines
5.3 KiB
C
116 lines
5.3 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2022 Justine Alexandra Roberts Tunney │
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│ │
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│ Permission to use, copy, modify, and/or distribute this software for │
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│ any purpose with or without fee is hereby granted, provided that the │
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│ above copyright notice and this permission notice appear in all copies. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
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│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
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│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
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│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
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│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
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│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
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│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
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│ PERFORMANCE OF THIS SOFTWARE. │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "ape/sections.internal.h"
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#include "libc/intrin/bits.h"
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#include "libc/runtime/internal.h"
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#include "libc/runtime/runtime.h"
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#include "libc/thread/tls.h"
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typedef char xmm_t __attribute__((__vector_size__(16), __aligned__(1)));
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privileged void __morph_tls(void) {
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#ifdef __x86_64__
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// We need to rewrite SysV _Thread_local code. You MUST use the
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// -mno-tls-direct-seg-refs flag which generates code like this
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//
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// 64 48 8b 0R4 25 00 00 00 00 mov %fs:0,%R
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// 64 48 03 0R4 25 00 00 00 00 add %fs:0,%R
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//
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// Which on Mac we can replace with this:
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//
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// 65 48 8b 0R4 25 30 00 00 00 mov %gs:0x30,%R
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//
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// Since we have no idea where the TLS instructions exist in the
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// binary, we need to disassemble the whole program image. This'll
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// potentially take a few milliseconds for some larger programs.
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//
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// We check `_tls_content` which is generated by the linker script
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// since it lets us determine ahead of time if _Thread_local vars
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// have actually been linked into this program.
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int n;
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uint64_t w;
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unsigned m, dis;
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unsigned char *p;
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__morph_begin();
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if (IsXnu()) {
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// Apple is quite straightforward to patch. We basically
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// just change the segment register, and the linear slot
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// address 0x30 was promised to us, according to Go team
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// https://github.com/golang/go/issues/23617
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dis = 0x30;
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} else {
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// MSVC __declspec(thread) generates binary code for this
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// %gs:0x1480 abi. So long as TlsAlloc() isn't called >64
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// times we should be good.
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dis = 0x1480 + __tls_index * 8;
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}
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// iterate over modifiable code looking for 9 byte instruction
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// this would take 30 ms using xed to enable tls on python.com
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for (p = _ereal; p + 9 <= __privileged_start; p += n) {
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// use sse to zoom zoom to fs register prefixes
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// that way it'll take 1 ms to morph python.com
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while (p + 9 + 16 <= __privileged_start) {
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if ((m = __builtin_ia32_pmovmskb128(
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*(xmm_t *)p == (xmm_t){0144, 0144, 0144, 0144, 0144, 0144, 0144,
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0144, 0144, 0144, 0144, 0144, 0144, 0144,
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0144, 0144}))) {
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m = __builtin_ctzll(m);
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p += m;
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break;
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} else {
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p += 16;
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}
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}
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// we're checking for the following expression:
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// 0144 == p[0] && // %fs
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// 0110 == (p[1] & 0373) && // rex.w (and ignore rex.r)
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// (0213 == p[2] || // mov reg/mem → reg (word-sized)
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// 0003 == p[2]) && // add reg/mem → reg (word-sized)
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// 0004 == (p[3] & 0307) && // mod/rm (4,reg,0) means sib → reg
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// 0045 == p[4] && // sib (5,4,0) → (rbp,rsp,0) → disp32
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// 0000 == p[5] && // displacement (von Neumann endian)
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// 0000 == p[6] && // displacement
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// 0000 == p[7] && // displacement
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// 0000 == p[8] // displacement
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w = READ64LE(p) & READ64LE("\377\373\377\307\377\377\377\377");
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if ((w == READ64LE("\144\110\213\004\045\000\000\000") ||
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w == READ64LE("\144\110\003\004\045\000\000\000")) &&
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!p[8]) {
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// now change the code
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p[0] = 0145; // change %fs to %gs
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p[5] = (dis & 0x000000ff) >> 000; // displacement
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p[6] = (dis & 0x0000ff00) >> 010; // displacement
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p[7] = (dis & 0x00ff0000) >> 020; // displacement
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p[8] = (dis & 0xff000000) >> 030; // displacement
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// advance to the next instruction
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n = 9;
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} else {
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n = 1;
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}
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}
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__morph_end();
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#endif
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}
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