Fix _Thread_local with fork() on Windows

libc/calls/wincrash.c

@@ -29,11 +29,11 @@
 #include "libc/sysv/consts/sicode.h"
 #include "libc/sysv/consts/sig.h"
 
-privileged unsigned __wincrash(struct NtExceptionPointers *ep) {
+unsigned __wincrash(struct NtExceptionPointers *ep) {
   int64_t rip;
   int sig, code;
   ucontext_t ctx;
-  STRACE("__wincrash");
+  STRACE("__wincrash rip=%lx", ep->ContextRecord->Rip);
 
   switch (ep->ExceptionRecord->ExceptionCode) {
     case kNtSignalBreakpoint:

libc/runtime/fork-nt.c

@@ -88,6 +88,7 @@ static inline textwindows ssize_t ForkIo(int64_t h, char *p, size_t n,
 static dontinline textwindows bool ForkIo2(int64_t h, void *buf, size_t n,
                                            bool32 (*fn)(), const char *sf) {
   ssize_t rc = ForkIo(h, buf, n, fn);
+  __tls_enabled = false;  // prevent tls crash in kprintf
   NTTRACE("%s(%ld, %p, %'zu) → %'zd% m", sf, h, buf, n, rc);
   return rc != -1;
 }
@@ -218,6 +219,9 @@ textwindows void WinMainForked(void) {
     AbortFork("CloseHandle");
   }
 
+  // turn tls back on
+  __enable_tls();
+
   // rewrap the stdin named pipe hack
   // since the handles closed on fork
   struct Fds *fds = VEIL("r", &g_fds);

third_party/xed/x86.h

@@ -27,6 +27,13 @@
 #define XED_HINT_TAKEN  4
 #define XED_HINT_ALTER  6
 
+#define XED_SEG_ES 1
+#define XED_SEG_CS 2
+#define XED_SEG_SS 3
+#define XED_SEG_DS 4
+#define XED_SEG_FS 5
+#define XED_SEG_GS 6
+
 #define xed_modrm_mod(M)           (((M)&0xff) >> 6)
 #define xed_modrm_reg(M)           (((M)&0b00111000) >> 3)
 #define xed_modrm_rm(M)            ((M)&7)

tool/build/fixupobj.c

@@ -26,6 +26,7 @@
 #include "libc/elf/struct/sym.h"
 #include "libc/errno.h"
 #include "libc/fmt/itoa.h"
+#include "libc/intrin/kprintf.h"
 #include "libc/intrin/safemacros.internal.h"
 #include "libc/log/check.h"
 #include "libc/log/log.h"
@@ -36,6 +37,7 @@
 #include "libc/sysv/consts/o.h"
 #include "libc/sysv/consts/prot.h"
 #include "third_party/getopt/getopt.h"
+#include "third_party/xed/x86.h"
 
 /**
  * @fileoverview GCC Codegen Fixer-Upper.
@@ -151,6 +153,41 @@ void OptimizeRelocations(Elf64_Ehdr *elf, size_t elfsize) {
   }
 }
 
+void CheckForTlsInPrivileged(const char *path, Elf64_Ehdr *elf,
+                             size_t elfsize) {
+  int err;
+  size_t m;
+  Elf64_Half i;
+  struct Op *op;
+  Elf64_Shdr *shdr;
+  unsigned char *p, *e;
+  Elf64_Xword symcount;
+  struct XedDecodedInst xedd;
+  for (i = 0; i < elf->e_shnum; ++i) {
+    shdr = GetElfSectionHeaderAddress(elf, elfsize, i);
+    if (shdr->sh_type == SHT_PROGBITS &&
+        startswith(GetElfSectionName(elf, elfsize, shdr), ".privileged")) {
+      p = (unsigned char *)((uintptr_t)elf + shdr->sh_offset);
+      e = p + shdr->sh_size;
+      for (; p < e; p += m) {
+        xed_decoded_inst_zero_set_mode(&xedd, XED_MACHINE_MODE_LONG_64);
+        err = xed_instruction_length_decode(&xedd, p, e - p);
+        if (err == XED_ERROR_NONE) {
+          m = xedd.length;
+          if (xedd.op.seg_ovd == XED_SEG_FS) {
+            kprintf("%s: thread local storage not allowed in privileged "
+                    "functions\n",
+                    path);
+            exit(1);
+          }
+        } else {
+          m = 1;
+        }
+      }
+    }
+  }
+}
+
 void RewriteObject(const char *path) {
   int fd;
   struct stat st;
@@ -166,6 +203,7 @@ void RewriteObject(const char *path) {
                     0)) == MAP_FAILED) {
       SysExit(__COUNTER__ + 1, "mmap", path);
     }
+    CheckForTlsInPrivileged(path, elf, st.st_size);
     OptimizeRelocations(elf, st.st_size);
     if (msync(elf, st.st_size, MS_ASYNC | MS_INVALIDATE)) {
       SysExit(__COUNTER__ + 1, "msync", path);