Make improvements

- Introduce ualarm() function
- Make rename() report EISEMPTY on Windows
- Always raise EINVAL upon open(O_RDONLY|O_TRUNC)
- Add macro so ./configure will detect SOCK_CLOEXEC
- Fix O_TRUNC without O_CREAT not working on Windows
- Let fcntl(F_SETFL) change O_APPEND status on Windows
- Make sure pwrite() / pread() report ESPIPE on sockets
- Raise ESPIPE on Windows when pwrite() is used on pipe
- Properly compute O_APPEND CreateFile() flags on Windows
- Don't require O_DIRECTORY to open directories on Windows
- Fix more instances of Windows reporting EISDIR and ENOTDIR
- Normalize EFTYPE and EMLINK to ELOOP on NetBSD and FreeBSD
- Make unlink() / rmdir() work on read-only files on Windows
- Validate UTF-8 on Windows paths to fix bug with overlong NUL
- Always print signal name to stderr when crashing due to SIG_DFL
- Fix Windows bug where denormalized paths >260 chars didn't work
- Block signals on BSDs when thread exits before trashing its own stack

libc/runtime/clone.c

@@ -20,6 +20,7 @@
 #include "libc/assert.h"
 #include "libc/atomic.h"
 #include "libc/calls/calls.h"
+#include "libc/calls/struct/sigset.h"
 #include "libc/calls/struct/ucontext-netbsd.internal.h"
 #include "libc/calls/syscall-sysv.internal.h"
 #include "libc/calls/wincrash.internal.h"
@@ -195,6 +196,9 @@ XnuThreadMain(void *pthread,                    // rdi
 
   func(arg, tid);
 
+  // avoid signal handler being triggered after we trash our stack
+  _sigblockall();
+
   // we no longer use the stack after this point
   // %rax = int bsdthread_terminate(%rdi = void *stackaddr,
   //                                %rsi = size_t freesize,
@@ -234,6 +238,8 @@ static wontreturn void FreebsdThreadMain(void *p) {
   struct CloneArgs *wt = p;
   *wt->ctid = wt->tid;
   wt->func(wt->arg, wt->tid);
+  // avoid signal handler being triggered after we trash our stack
+  _sigblockall();
   // we no longer use the stack after this point
   // void thr_exit(%rdi = long *state);
   asm volatile("movl\t$0,%0\n\t"       // *wt->ztid = 0
@@ -349,6 +355,8 @@ static wontreturn void NetbsdThreadMain(void *arg,                 // rdi
   ax = sys_gettid();
   *ctid = ax;
   func(arg, ax);
+  // avoid signal handler being triggered after we trash our stack
+  _sigblockall();
   // we no longer use the stack after this point
   // %eax = int __lwp_exit(void);
   asm volatile("movl\t$0,%2\n\t"  // *wt->ztid = 0