[LIBC] Fix `getrandom` success return value

[goldstein.w.n]

Summary

getrandom should return the number of bytes successfully set on
success, not 0.

[SchrodingerZhu]

• publickey - [e-mail] - 0xF81EA6F4.asc677 BDownload
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[michaelrj]

libc/test/src/sys/random/linux/getrandom_test.cpp

35

I'm not sure why the mod operation is here, maybe add a comment explaining?

[goldstein.w.n]

libc/test/src/sys/random/linux/getrandom_test.cpp

35

I'm not sure why the mod operation is here, maybe add a comment explaining?

Its just meant to be a compromise between not doing every single value and getting a decent spread. Could also be rand % 64 or something like that, but figured that might make test harder to reproduce.

64 should probably be a prime in retrospect.

[goldstein.w.n]

64 -> 61 (for prime) + comment explaining rationale

[michaelrj]

libc/test/src/sys/random/linux/getrandom_test.cpp

35

Given that the range tested is only 8192 it's not a big deal to do the whole range. The pi estimation test below is performing 10,000,000 samples (with two calls each), and that's having a much greater effect on the runtime of this test.

[goldstein.w.n]

Test all sizes

[sivachandra]

OK from my side but I have arrived late here. Please wait for @michaelrj who is leading this review.

[michaelrj]

LGTM, feel free to land

libc/src/sys/random/linux/getrandom.cpp

 
 LLVM_LIBC_FUNCTION(ssize_t, getrandom,
                    (void *buf, size_t buflen, unsigned int flags)) {
   long ret = __llvm_libc::syscall_impl(SYS_getrandom, buf, buflen, flags);
   if (ret < 0) {
     libc_errno = -ret;
     return -1;
   }
-  return 0;
+  return ret;
 }
 
 } // namespace __llvm_libc

libc/test/src/sys/random/linux/getrandom_test.cpp

 TEST(LlvmLibcGetRandomTest, InvalidBuffer) {
   using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
 
   libc_errno = 0;
   ASSERT_THAT(__llvm_libc::getrandom(nullptr, 65536, 0), Fails(EFAULT));
   libc_errno = 0;
 }
 
+TEST(LlvmLibcGetRandomTest, ReturnsSize) {
+  static constexpr size_t SIZE = 8192;
+  uint8_t buf[SIZE];
+  for (size_t i = 0; i < SIZE; ++i) {
+    // Without GRND_RANDOM set this should never fail.
+    ASSERT_EQ(__llvm_libc::getrandom(buf, i, 0), static_cast<ssize_t>(i));
+  }
+}
+
 TEST(LlvmLibcGetRandomTest, PiEstimation) {
   static constexpr size_t LIMIT = 10000000;
   static constexpr double PI = 3.14159265358979;
 
   auto generator = []() {
     uint16_t data;
     __llvm_libc::getrandom(&data, sizeof(data), 0);
     return data;