[libc] Fix compilation on 32-bit systems

[mikhail.ramalho]

Summary

This fixes the following compilation error: no known conversion from 'off_t *'
(aka 'long long *') to 'long' for 5th argument.

Since pointers are 32-bit long anyway, casting it to long shouldn't be a
problem. Tested on rv32.

[michaelrj]

Change is fine, but in general C++ style casts are preferred over C style casts.

[mikhail.ramalho]

• Removed old SYS_llseek and reuse SYS__llseek
• Rebased

[sivachandra]

libc/src/unistd/linux/lseek.cpp

29–30

May be you should keep the cast to uint64_t here because off_t is a signed type?

31

At this point, the best would probably be:

#ifdef SYS_llseek
constexpr long LLSEEK_SYSCALL_NO = SYS_llseek;
#elif defined(SYS__llseek)
constexpr long LSEEK_SYSCALL_NO = SYS__llseek;
#else
#error ...
#endif
int ret = __llvm_libc::syscall_impl<int>(LLSEEK_SYSCALL_NO, fd, offset >> 32,
                                         offset, &result, whence);

[mikhail.ramalho]

• added LSEEK_SYSCALL_NO
• added cast to uint64_t back

libc/src/unistd/linux/lseek.cpp

 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(off_t, lseek, (int fd, off_t offset, int whence)) {
   off_t result;
 #ifdef SYS_lseek
   int ret = __llvm_libc::syscall_impl<int>(SYS_lseek, fd, offset, whence);
   result = ret;
-#elif defined(SYS_llseek)
-  long ret = __llvm_libc::syscall_impl(SYS_llseek, fd,
-                                       (long)(((uint64_t)(offset)) >> 32),
-                                       (long)offset, &result, whence);
-  result = ret;
+#elif defined(SYS_llseek) || defined(SYS__llseek)
+#ifdef SYS_llseek
+  constexpr long LLSEEK_SYSCALL_NO = SYS_llseek;
 #elif defined(SYS__llseek)
-  int ret = __llvm_libc::syscall_impl<int>(SYS__llseek, fd, offset >> 32,
-                                           offset, &result, whence);
+  constexpr long LLSEEK_SYSCALL_NO = SYS__llseek;
+#endif
+  uint64_t offset_64 = static_cast<uint64_t>(offset);
+  int ret = __llvm_libc::syscall_impl<int>(
+      LLSEEK_SYSCALL_NO, fd, offset_64 >> 32, offset_64, &result, whence);
 #else
 #error "lseek, llseek and _llseek syscalls not available."
 #endif
 
   if (ret < 0) {
     libc_errno = -ret;
     return -1;
   }
   return result;
 }
 
 } // namespace __llvm_libc