Fix corner case in Linux stack mappings

We need to make sure no existing mappings exist between the
MAP_GROWSDOWN page and the guard page, since otherwise it's
not going to be able to grow down thus causing difficult to
troubleshoot failures.

Author: jart

libc/integral/normalize.inc

@@ -68,7 +68,7 @@
 
 /* TODO(jart): Remove this in favor of GetStackSize() */
 #if defined(COSMO) && (defined(MODE_DBG) || defined(__SANITIZE_ADDRESS__))
-#define STACKSIZE 524288 /* 512kb stack */
+#define STACKSIZE 262144 /* 256kb stack */
 #elif defined(COSMO)
 #define STACKSIZE 65536 /* 64kb stack */
 #else

libc/intrin/stracef.greg.c

@@ -16,8 +16,8 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
-#include "libc/intrin/strace.internal.h"
 #include "libc/intrin/kprintf.h"
+#include "libc/intrin/strace.internal.h"
 #include "libc/runtime/runtime.h"
 
 privileged void __stracef(const char *fmt, ...) {

libc/runtime/mmap.c

@@ -361,6 +361,10 @@ static noasan inline void *Mmap(void *addr, size_t size, int prot, int flags,
       f |= MAP_STACK_openbsd;
       needguard = true;
     } else if (IsLinux()) {
+      // make sure there's no existing stuff existing between our stack
+      // starting page and the bottom guard page, since that would stop
+      // our stack page from growing down.
+      _npassert(!sys_munmap(p, size));
       // by default MAP_GROWSDOWN will auto-allocate 10mb of pages. it's
       // supposed to stop growing if an adjacent allocation exists, to
       // prevent your stacks from overlapping on each other. we're not
@@ -376,8 +380,9 @@ static noasan inline void *Mmap(void *addr, size_t size, int prot, int flags,
               .addr == MAP_FAILED) {
         return MAP_FAILED;
       }
-      sys_mmap(p, PAGESIZE, PROT_NONE, MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS,
-               -1, 0);
+      _npassert(sys_mmap(p, PAGESIZE, PROT_NONE,
+                         MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0)
+                    .addr == p);
       dm.addr = p;
       return FinishMemory(p, size, prot, flags, fd, off, f, x, n, dm);
     } else {

libc/runtime/mprotect.c

@@ -16,12 +16,12 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
-#include "libc/intrin/strace.internal.h"
 #include "libc/calls/syscall-sysv.internal.h"
 #include "libc/dce.h"
 #include "libc/errno.h"
 #include "libc/intrin/describeflags.internal.h"
 #include "libc/intrin/likely.h"
+#include "libc/intrin/strace.internal.h"
 #include "libc/runtime/internal.h"
 #include "libc/sysv/consts/prot.h"
 

libc/stdio/fflush.internal.h

@@ -1,8 +1,9 @@
 #ifndef COSMOPOLITAN_LIBC_STDIO_FFLUSH_H_
 #define COSMOPOLITAN_LIBC_STDIO_FFLUSH_H_
 #include "libc/intrin/nopl.internal.h"
-#include "libc/thread/thread.h"
 #include "libc/stdio/stdio.h"
+#include "libc/thread/thread.h"
+#include "libc/thread/tls.h"
 #if !(__ASSEMBLER__ + __LINKER__ + 0)
 COSMOPOLITAN_C_START_
 

libc/sysv/consts.sh

@@ -579,8 +579,6 @@ syscon	sicode	SYS_USER_DISPATCH			2			-1			-1			-1			-1			-1			# SIGSYS; syscall
 #	sigaltstack() values
 #
 #	group	name					GNU/Systemd		XNU's Not UNIX!		FreeBSD			OpenBSD			NetBSD			The New Technology	Commentary
-syscon	ss	SIGSTKSZ				8192			131072			34816			28672			28672			8192			# overlaid with FRAMESIZE; you need to #undef SIGSTKSZ to access this symbol
-syscon	ss	MINSIGSTKSZ				2048			32768			2048			12288			8192			2048			# overlaid with 32768; you need to #undef MINSIGSTKSZ to access this symbol
 syscon	ss	SS_ONSTACK				1			1			1			1			1			1			# unix consensus
 syscon	ss	SS_DISABLE				2			4			4			4			4			2			# bsd consensus
 

libc/sysv/consts/MINSIGSTKSZ.s

@@ -3,15 +3,13 @@
 #if !(__ASSEMBLER__ + __LINKER__ + 0)
 COSMOPOLITAN_C_START_
 
-extern const size_t SIGSTKSZ;
-extern const size_t MINSIGSTKSZ;
 extern const int SS_DISABLE;
 
 COSMOPOLITAN_C_END_
 #endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
 
-#define SIGSTKSZ    FRAMESIZE
-#define MINSIGSTKSZ 32768
+#define SIGSTKSZ    32768
+#define MINSIGSTKSZ 32768 /* xnu defines the highest minimum */
 #define SS_ONSTACK  1
 #define SS_DISABLE  SS_DISABLE