[base] Only use memfd_create when available

The use of memfd_create causes V8 to require glibc 2.27 which wasn't
previously needed. This CL rewrites the affected code to check at
runtime whether memfd_create is available and otherwise use mkstemp.

Bug: v8:12682
Change-Id: I84dc3f5ab7504cec2b599bc92501ddecc2ae22cf
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3516870Reviewed-by: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Samuel Groß <saelo@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79486}

src/base/platform/platform-posix.cc

@@ -46,8 +46,11 @@
 #include <atomic>
 #endif
 
+#if V8_OS_DARWIN || V8_OS_LINUX
+#include <dlfcn.h>  // for dlsym
+#endif
+
 #if V8_OS_DARWIN
-#include <dlfcn.h>
 #include <mach/mach.h>
 #endif
 
@@ -577,8 +580,18 @@ void OS::FreeAddressSpaceReservation(AddressSpaceReservation reservation) {
 // static
 PlatformSharedMemoryHandle OS::CreateSharedMemoryHandleForTesting(size_t size) {
 #if V8_OS_LINUX && !V8_OS_ANDROID
-  const char* name = "V8MemFDForTesting";
-  int fd = memfd_create(name, MFD_CLOEXEC);
+  // Use memfd_create if available, otherwise mkstemp.
+  using memfd_create_t = int (*)(const char*, unsigned int);
+  memfd_create_t memfd_create =
+      reinterpret_cast<memfd_create_t>(dlsym(RTLD_DEFAULT, "memfd_create"));
+  int fd = -1;
+  if (memfd_create) {
+    fd = memfd_create("V8MemFDForTesting", MFD_CLOEXEC);
+  } else {
+    char filename[] = "/tmp/v8_tmp_file_for_testing_XXXXXX";
+    fd = mkstemp(filename);
+    if (fd != -1) CHECK_EQ(0, unlink(filename));
+  }
   if (fd == -1) return kInvalidSharedMemoryHandle;
   CHECK_EQ(0, ftruncate(fd, size));
   return SharedMemoryHandleFromFileDescriptor(fd);