Initial import

libc/runtime/arch_prctl.c

@@ -0,0 +1,184 @@
+/*-*- 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 2020 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ This program is free software; you can redistribute it and/or modify         │
+│ it under the terms of the GNU General Public License as published by         │
+│ the Free Software Foundation; version 2 of the License.                      │
+│                                                                              │
+│ This program is distributed in the hope that it will be useful, but          │
+│ WITHOUT ANY WARRANTY; without even the implied warranty of                   │
+│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU             │
+│ General Public License for more details.                                     │
+│                                                                              │
+│ You should have received a copy of the GNU General Public License            │
+│ along with this program; if not, write to the Free Software                  │
+│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA                │
+│ 02110-1301 USA                                                               │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "ape/lib/pc.h"
+#include "libc/bits/bits.h"
+#include "libc/calls/calls.h"
+#include "libc/dce.h"
+#include "libc/nexgen32e/msr.h"
+#include "libc/nexgen32e/x86feature.h"
+#include "libc/runtime/interruptiblecall.h"
+#include "libc/sysv/consts/sig.h"
+#include "libc/sysv/errfuns.h"
+
+/**
+ * @fileoverview Memory segmentation system calls.
+ *
+ * This whole file basically does:
+ *
+ *     mov foo,%fs
+ *     mov foo,%gs
+ *     mov %fs,foo
+ *     mov %gs,foo
+ *
+ * Which is nontrivial due to the limitless authoritarianism of
+ * operating systems.
+ */
+
+int arch_prctl$sysv(int, int64_t) hidden;
+
+static inline int arch_prctl$fsgsbase(int code, int64_t addr) {
+  switch (code) {
+    case ARCH_SET_GS:
+      asm volatile("wrgsbase\t%0" : /* no outputs */ : "r"(addr));
+      return 0;
+    case ARCH_SET_FS:
+      asm volatile("wrfsbase\t%0" : /* no outputs */ : "r"(addr));
+      return 0;
+    case ARCH_GET_GS:
+      asm volatile("rdgsbase\t%0" : "=r"(*(int64_t *)addr));
+      return 0;
+    case ARCH_GET_FS:
+      asm volatile("rdfsbase\t%0" : "=r"(*(int64_t *)addr));
+      return 0;
+    default:
+      return einval();
+  }
+}
+
+static int arch_prctl$msr(int code, int64_t addr) {
+  switch (code) {
+    case ARCH_SET_GS:
+      wrmsr(MSR_IA32_GS_BASE, addr);
+      return 0;
+    case ARCH_SET_FS:
+      wrmsr(MSR_IA32_FS_BASE, addr);
+      return 0;
+    case ARCH_GET_GS:
+      *(int64_t *)addr = rdmsr(MSR_IA32_GS_BASE);
+      return 0;
+    case ARCH_GET_FS:
+      *(int64_t *)addr = rdmsr(MSR_IA32_FS_BASE);
+      return 0;
+    default:
+      return einval();
+  }
+}
+
+static int arch_prctl$freebsd(int code, int64_t addr) {
+  switch (code) {
+    case ARCH_GET_FS:
+      return arch_prctl$sysv(128, addr);
+    case ARCH_SET_FS:
+      return arch_prctl$sysv(129, addr);
+    case ARCH_GET_GS:
+      return arch_prctl$sysv(130, addr);
+    case ARCH_SET_GS:
+      return arch_prctl$sysv(131, addr);
+    default:
+      return einval();
+  }
+}
+
+static int arch_prctl$xnu(int code, int64_t addr) {
+  int ax;
+  switch (code) {
+    case ARCH_SET_GS:
+      asm volatile("syscall"
+                   : "=a"(ax)
+                   : "0"(0x3000003), "D"(addr - 0x8a0 /* wat */)
+                   : "rcx", "r11", "memory", "cc");
+      return ax;
+    case ARCH_GET_FS:
+    case ARCH_SET_FS:
+    case ARCH_GET_GS:
+      return enosys();
+    default:
+      return einval();
+  }
+}
+
+static int arch_prctl$openbsd(int code, int64_t addr) {
+  int64_t rax;
+  switch (code) {
+    case ARCH_GET_FS:
+      asm volatile("syscall"
+                   : "=a"(rax)
+                   : "0"(0x014a /* __get_tcb */)
+                   : "rcx", "r11", "cc", "memory");
+      *(int64_t *)addr = rax;
+      return 0;
+    case ARCH_SET_FS:
+      asm volatile("syscall"
+                   : "=a"(rax)
+                   : "0"(0x0149 /* __set_tcb */), "D"(addr)
+                   : "rcx", "r11", "cc", "memory");
+      return 0;
+    case ARCH_GET_GS:
+    case ARCH_SET_GS:
+      return enosys();
+    default:
+      return einval();
+  }
+}
+
+static char g_fsgs_once;
+static struct InterruptibleCall g_fsgs_icall;
+
+/**
+ * Don't bother.
+ */
+int arch_prctl(int code, int64_t addr) {
+  void *fn = arch_prctl$fsgsbase;
+  if (!g_fsgs_once) {
+    g_fsgs_once = true;
+    if (X86_HAVE(FSGSBASE)) {
+      g_fsgs_icall.sig = SIGILL;
+      if (interruptiblecall(&g_fsgs_icall, fn, code, addr, 0, 0) != -1 &&
+          g_fsgs_icall.returnval != -1) {
+        /* ivybridge+ (2012) lets us change segment registers without
+           needing a 700ns system call. cpuid and /proc/cpuinfo will both
+           report it's available; unfortunately, operating systems have an
+           added ability to restrict this feature in %cr4, which we're not
+           even allowed to read lool */
+        g_fsgs_once = 2;
+        return 0;
+      }
+    }
+  }
+  if (g_fsgs_once == 2) {
+    return arch_prctl$fsgsbase(code, addr);
+  }
+  switch (hostos) {
+    case METAL:
+      return arch_prctl$msr(code, addr);
+    case FREEBSD:
+      /* claims support but it appears not */
+      return arch_prctl$freebsd(code, addr);
+    case OPENBSD:
+      return arch_prctl$openbsd(code, addr);
+    case LINUX:
+      return arch_prctl$sysv(code, addr);
+    case XNU:
+      /* probably won't work */
+      return arch_prctl$xnu(code, addr);
+    default:
+      return enosys();
+  }
+}