[libc] Implement fcntl when only SYS_fcntl64 is available

This patch tries to implement fcntl with either SYS_fcntl or
SYS_fcntl64, and also changes a test case to call the fcntl function
instead of using the syscall

Author: mikhailramalho

libc/src/__support/OSUtil/linux/fcntl.cpp

@@ -22,6 +22,14 @@
 namespace LIBC_NAMESPACE::internal {
 
 int fcntl(int fd, int cmd, void *arg) {
+#if SYS_fcntl
+  constexpr auto FCNTL_SYSCALL_ID = SYS_fcntl;
+#elif defined(SYS_fcntl64)
+  constexpr auto FCNTL_SYSCALL_ID = SYS_fcntl64;
+#else
+#error "fcntl and fcntl64 syscalls not available."
+#endif
+
   switch (cmd) {
   case F_OFD_SETLKW: {
     struct flock *flk = reinterpret_cast<struct flock *>(arg);
@@ -33,7 +41,7 @@ int fcntl(int fd, int cmd, void *arg) {
     flk64.l_len = flk->l_len;
     flk64.l_pid = flk->l_pid;
     // create a syscall
-    return LIBC_NAMESPACE::syscall_impl<int>(SYS_fcntl, fd, cmd, &flk64);
+    return LIBC_NAMESPACE::syscall_impl<int>(FCNTL_SYSCALL_ID, fd, cmd, &flk64);
   }
   case F_OFD_GETLK:
   case F_OFD_SETLK: {
@@ -46,7 +54,8 @@ int fcntl(int fd, int cmd, void *arg) {
     flk64.l_len = flk->l_len;
     flk64.l_pid = flk->l_pid;
     // create a syscall
-    int retVal = LIBC_NAMESPACE::syscall_impl<int>(SYS_fcntl, fd, cmd, &flk64);
+    int retVal =
+        LIBC_NAMESPACE::syscall_impl<int>(FCNTL_SYSCALL_ID, fd, cmd, &flk64);
     // On failure, return
     if (retVal == -1)
       return -1;
@@ -67,8 +76,8 @@ int fcntl(int fd, int cmd, void *arg) {
   }
   case F_GETOWN: {
     struct f_owner_ex fex;
-    int ret =
-        LIBC_NAMESPACE::syscall_impl<int>(SYS_fcntl, fd, F_GETOWN_EX, &fex);
+    int ret = LIBC_NAMESPACE::syscall_impl<int>(FCNTL_SYSCALL_ID, fd,
+                                                F_GETOWN_EX, &fex);
     if (ret >= 0)
       return fex.type == F_OWNER_PGRP ? -fex.pid : fex.pid;
     libc_errno = -ret;
@@ -77,7 +86,7 @@ int fcntl(int fd, int cmd, void *arg) {
   // The general case
   default: {
     int retVal = LIBC_NAMESPACE::syscall_impl<int>(
-        SYS_fcntl, fd, cmd, reinterpret_cast<void *>(arg));
+        FCNTL_SYSCALL_ID, fd, cmd, reinterpret_cast<void *>(arg));
     if (retVal >= 0) {
       return retVal;
     }

libc/test/src/sys/mman/linux/CMakeLists.txt

@@ -138,6 +138,7 @@ add_libc_unittest(
     libc.include.sys_mman
     libc.include.sys_syscall
     libc.src.errno.errno
+    libc.src.fcntl.fcntl
     libc.src.sys.mman.shm_open
     libc.src.sys.mman.shm_unlink
     libc.src.sys.mman.mmap

libc/test/src/sys/mman/linux/shm_test.cpp

@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "src/__support/OSUtil/syscall.h"
+#include "src/fcntl/fcntl.h"
 #include "src/sys/mman/mmap.h"
 #include "src/sys/mman/munmap.h"
 #include "src/sys/mman/shm_open.h"
@@ -29,9 +30,7 @@ TEST(LlvmLibcShmTest, Basic) {
               returns(GE(0)).with_errno(EQ(0)));
 
   // check that FD_CLOEXEC is set by default.
-  // TODO: use fcntl when implemented.
-  // https://github.com/llvm/llvm-project/issues/84968
-  long flag = LIBC_NAMESPACE::syscall_impl(SYS_fcntl, fd, F_GETFD);
+  long flag = LIBC_NAMESPACE::fcntl(fd, F_GETFD);
   ASSERT_GE(static_cast<int>(flag), 0);
   EXPECT_NE(static_cast<int>(flag) & FD_CLOEXEC, 0);