4 files changed, 18 insertions, 3 deletions
diff --git a/libc/src/__support/OSUtil/linux/auxv.h b/libc/src/__support/OSUtil/linux/auxv.h
index 894868a..9c07c54 100644
--- a/libc/src/__support/OSUtil/linux/auxv.h
+++ b/libc/src/__support/OSUtil/linux/auxv.h
@@ -16,6 +16,7 @@
 
 #include <linux/auxvec.h> // For AT_ macros
 #include <linux/mman.h>   // For mmap flags
+#include <linux/param.h>  // For EXEC_PAGESIZE
 #include <linux/prctl.h>  // For prctl
 #include <sys/syscall.h>  // For syscall numbers
 
@@ -90,7 +91,7 @@ LIBC_INLINE void Vector::fallback_initialize_unsync() {
                                      PROT_READ | PROT_WRITE,
                                      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
   // We do not proceed if mmap fails.
-  if (mmap_ret <= 0)
+  if (!linux_utils::is_valid_mmap(mmap_ret))
     return;
 
   // Initialize the auxv array with AT_NULL entries.
diff --git a/libc/src/__support/OSUtil/linux/syscall.h b/libc/src/__support/OSUtil/linux/syscall.h
index 24e0fca..0e25618 100644
--- a/libc/src/__support/OSUtil/linux/syscall.h
+++ b/libc/src/__support/OSUtil/linux/syscall.h
@@ -12,6 +12,7 @@
 #include "src/__support/CPP/bit.h"
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"
+#include "src/__support/macros/optimization.h"
 #include "src/__support/macros/properties/architectures.h"
 
 #ifdef LIBC_TARGET_ARCH_IS_X86_32
@@ -34,6 +35,19 @@ LIBC_INLINE R syscall_impl(long __number, Ts... ts) {
   return cpp::bit_or_static_cast<R>(syscall_impl(__number, (long)ts...));
 }
 
+// Linux-specific function for checking
+namespace linux_utils {
+LIBC_INLINE_VAR constexpr unsigned long MAX_ERRNO = 4095;
+// Ideally, this should be defined using PAGE_OFFSET
+// However, that is a configurable parameter. We mimic kernel's behavior
+// by checking against MAX_ERRNO.
+template <typename PointerLike>
+LIBC_INLINE constexpr bool is_valid_mmap(PointerLike ptr) {
+  long addr = cpp::bit_cast<long>(ptr);
+  return LIBC_LIKELY(addr > 0 || addr < -static_cast<long>(MAX_ERRNO));
+}
+} // namespace linux_utils
+
 } // namespace LIBC_NAMESPACE_DECL
 
 #endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_LINUX_SYSCALL_H
diff --git a/libc/src/__support/threads/linux/thread.cpp b/libc/src/__support/threads/linux/thread.cpp
index d9e479ee..4f1e911 100644
--- a/libc/src/__support/threads/linux/thread.cpp
+++ b/libc/src/__support/threads/linux/thread.cpp
@@ -100,7 +100,7 @@ LIBC_INLINE ErrorOr<void *> alloc_stack(size_t stacksize, size_t guardsize) {
       -1,                          // Not backed by any file
       0                            // No offset
   );
-  if (mmap_result < 0 && (uintptr_t(mmap_result) >= UINTPTR_MAX - size))
+  if (!linux_utils::is_valid_mmap(mmap_result))
     return Error{int(-mmap_result)};
 
   if (guardsize) {
diff --git a/libc/src/sys/mman/linux/mmap.cpp b/libc/src/sys/mman/linux/mmap.cpp
index 33f9fe8..76a6611 100644
--- a/libc/src/sys/mman/linux/mmap.cpp
+++ b/libc/src/sys/mman/linux/mmap.cpp
@@ -56,7 +56,7 @@ LLVM_LIBC_FUNCTION(void *, mmap,
   // However, since a valid return address cannot be within the last page, a
   // return value corresponding to a location in the last page is an error
   // value.
-  if (ret < 0 && ret > -EXEC_PAGESIZE) {
+  if (!linux_utils::is_valid_mmap(ret)) {
     libc_errno = static_cast<int>(-ret);
     return MAP_FAILED;
   }