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69f4152f38
We had previously not enabled TLS in MODE=tiny in order to keep the smallest example programs (e.g. life.com) just 16kb in size. But it was error prone doing that, so now we just always enable it because this change uses hacks to ensure it won't increase life.com's size. This change also fixes a bug on NetBSD, where signal handlers would break thread local storage if SA_SIGINFO was being used. This looks like it might be a bug in NetBSD, but it's got a simple workaround.
270 lines
11 KiB
C
270 lines
11 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 "libc/assert.h"
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#include "libc/bits/bits.h"
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#include "libc/bits/weaken.h"
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#include "libc/calls/calls.h"
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#include "libc/calls/strace.internal.h"
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#include "libc/calls/syscall-sysv.internal.h"
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#include "libc/dce.h"
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#include "libc/errno.h"
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#include "libc/intrin/kprintf.h"
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#include "libc/log/libfatal.internal.h"
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#include "libc/macros.internal.h"
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#include "libc/nexgen32e/threaded.h"
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#include "libc/nt/thread.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/str/str.h"
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#include "libc/sysv/consts/nrlinux.h"
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#include "libc/thread/thread.h"
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#include "third_party/xed/x86.h"
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#define __NR_sysarch 0x000000a5 // freebsd+netbsd
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#define AMD64_SET_GSBASE 131 // freebsd
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#define AMD64_SET_FSBASE 129 // freebsd
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#define X86_SET_GSBASE 16 // netbsd
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#define X86_SET_FSBASE 17 // netbsd
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#define __NR___set_tcb 0x00000149
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#define __NR__lwp_setprivate 0x0000013d
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#define __NR_thread_fast_set_cthread_self 0x03000003
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#define _TLSZ ((intptr_t)_tls_size)
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#define _TLDZ ((intptr_t)_tdata_size)
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#define _TIBZ sizeof(struct cthread_descriptor_t)
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typedef char xmm_t __attribute__((__vector_size__(16), __aligned__(1)));
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__msabi extern typeof(TlsAlloc) *const __imp_TlsAlloc;
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extern unsigned char __tls_mov_nt_rax[];
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extern unsigned char __tls_add_nt_rax[];
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_Alignas(long) static char __static_tls[5008];
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/**
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* Enables thread local storage.
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*
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* This function is always called by the core runtime to guarantee TLS
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* is always available to your program. You must build your code using
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* -mno-tls-direct-seg-refs if you want to use _Thread_local.
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*
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* You can use __get_tls() to get the linear address of your tib. When
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* accessing TLS via privileged code you must use __get_tls_privileged
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* because we need code morphing to support The New Technology and XNU
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*
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* On XNU and The New Technology, this function imposes 1ms of latency
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* during startup for larger binaries like Python.
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*
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* If you don't want TLS and you're sure you're not using it, then you
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* can disable it as follows:
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*
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* int main() {
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* __tls_enabled = false;
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* // do stuff
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* }
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*
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* This is useful if you want to wrestle back control of %fs using the
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* arch_prctl() function. However, such programs might not be portable
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* and your `errno` variable also won't be thread safe anymore.
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*/
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privileged void __enable_tls(void) {
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STRACE("__enable_tls()");
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// allocate tls memory for main process
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//
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// %fs Linux/BSDs
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// │
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// _Thread_local │ __get_tls()
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// ┌───┬──────────┬──────────┼───┐
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// │pad│ .tdata │ .tbss │tib│
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// └───┴──────────┴──────────┼───┘
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// │
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// Windows/Mac %gs
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//
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size_t siz;
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cthread_t tib;
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char *mem, *tls;
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siz = ROUNDUP(_TLSZ + _TIBZ, alignof(__static_tls));
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if (siz <= sizeof(__static_tls)) {
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// if tls requirement is small then use the static tls block
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// which helps avoid a system call for appes with little tls
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// this is crucial to keeping life.com 16 kilobytes in size!
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_Static_assert(alignof(__static_tls) >= alignof(cthread_t));
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mem = __static_tls;
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} else {
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// if this binary needs a hefty tls block then we'll bank on
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// malloc() being linked, which links _mapanon(). otherwise
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// if you exceed this, you need to STATIC_YOINK("_mapanon").
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// please note that it's probably too early to call calloc()
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assert(weaken(_mapanon));
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siz = ROUNDUP(siz, FRAMESIZE);
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mem = weaken(_mapanon)(siz);
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assert(mem);
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}
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tib = (cthread_t)(mem + siz - _TIBZ);
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tls = mem + siz - _TIBZ - _TLSZ;
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tib->self = tib;
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tib->self2 = tib;
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tib->err = __errno;
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if (IsLinux()) {
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// gnu/systemd guarantees pid==tid for the main thread so we can
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// avoid issuing a superfluous system call at startup in program
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tib->tid = __pid;
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} else {
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tib->tid = sys_gettid();
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}
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__repmovsb(tls, _tdata_start, _TLDZ);
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// ask the operating system to change the x86 segment register
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int ax, dx;
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if (IsWindows()) {
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__tls_index = __imp_TlsAlloc();
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assert(0 <= __tls_index && __tls_index < 64);
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asm("mov\t%1,%%gs:%0" : "=m"(*((long *)0x1480 + __tls_index)) : "r"(tib));
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} else if (IsFreebsd()) {
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asm volatile("syscall"
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: "=a"(ax)
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: "0"(__NR_sysarch), "D"(AMD64_SET_FSBASE), "S"(tib)
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: "rcx", "r11", "memory", "cc");
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} else if (IsNetbsd()) {
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// netbsd has sysarch(X86_SET_FSBASE) but we can't use that because
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// signal handlers will cause it to be reset due to net setting the
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// _mc_tlsbase field in struct mcontext_netbsd.
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asm volatile("syscall"
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: "=a"(ax), "=d"(dx)
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: "0"(__NR__lwp_setprivate), "D"(tib)
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: "rcx", "r11", "memory", "cc");
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} else if (IsXnu()) {
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asm volatile("syscall"
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: "=a"(ax)
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: "0"(__NR_thread_fast_set_cthread_self),
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"D"((intptr_t)tib - 0x30)
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: "rcx", "r11", "memory", "cc");
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} else if (IsOpenbsd()) {
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asm volatile("syscall"
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: "=a"(ax)
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: "0"(__NR___set_tcb), "D"(tib)
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: "rcx", "r11", "memory", "cc");
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} else {
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asm volatile("syscall"
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: "=a"(ax)
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: "0"(__NR_linux_arch_prctl), "D"(ARCH_SET_FS), "S"(tib)
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: "rcx", "r11", "memory");
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}
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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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// Whereas on Windows we'll replace it with this:
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//
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// 0f 1f 40 00 fatnop4
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// e8 xx xx xx xx call __tls_mov_nt_%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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if ((intptr_t)_tls_content && (IsWindows() || IsXnu())) {
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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,
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0144, 0144, 0144, 0144, 0144, 0144,
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0144, 0144, 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] && // rex.w (64-bit operand size)
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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\377\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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}
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// we are now allowed to use tls
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// setting this variable
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__tls_enabled = true;
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}
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