Make getentropy() faster

jart · Oct 11, 2024 · 000d6db · 000d6db
1 parent 17a85e4
commit 000d6db
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Showing 2 changed files with 19 additions and 19 deletions.
diff --git a/libc/stdio/getentropy.c b/libc/stdio/getentropy.c
@@ -17,17 +17,16 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/blockcancel.internal.h"
-#include "libc/calls/struct/sigset.internal.h"
 #include "libc/calls/syscall_support-sysv.internal.h"
 #include "libc/dce.h"
+#include "libc/errno.h"
 #include "libc/intrin/strace.h"
-#include "libc/stdio/rand.h"
 #include "libc/sysv/errfuns.h"
 
 int sys_getentropy(void *, size_t) asm("sys_getrandom");
 
 /**
- * Returns random seeding bytes, the XNU/OpenBSD way.
+ * Returns random seeding bytes, the POSIX way.
  *
  * @return 0 on success, or -1 w/ errno
  * @raise EFAULT if the `n` bytes at `p` aren't valid memory
@@ -41,17 +40,23 @@ int getentropy(void *p, size_t n) {
   } else if ((!p && n)) {
     rc = efault();
   } else if (IsXnu() || IsOpenbsd()) {
-    if (sys_getentropy(p, n))
-      notpossible;
-    rc = 0;
+    rc = sys_getentropy(p, n);
   } else {
-    BLOCK_SIGNALS;
+    ssize_t got;
     BLOCK_CANCELATION;
-    if (__getrandom(p, n, 0) != n)
-      notpossible;
-    ALLOW_CANCELATION;
-    ALLOW_SIGNALS;
     rc = 0;
+    for (size_t i = 0; i < n; i += got) {
+      got = __getrandom(p + i, n - i, 0);
+      if (got == -1) {
+        if (errno == EAGAIN || errno == EINTR) {
+          got = 0;
+        } else {
+          rc = -1;
+          break;
+        }
+      }
+    }
+    ALLOW_CANCELATION;
   }
   STRACE("getentropy(%p, %'zu) → %'ld% m", p, n, rc);
   return rc;

diff --git a/test/libc/stdio/getentropy_test.c b/test/libc/stdio/getentropy_test.c
@@ -33,8 +33,6 @@
 #include "libc/testlib/testlib.h"
 #include "libc/thread/thread.h"
 #ifndef __aarch64__
-// TODO(jart): Make this test less resource intensive.
-// TODO(jart): Why can EINTR happen on Windows?
 
 atomic_int done;
 atomic_int ready;
@@ -51,11 +49,9 @@ void *TortureWorker(void *arg) {
   ASSERT_SYS(0, 0, sigprocmask(SIG_SETMASK, &ss, 0));
   ready = true;
   while (!done) {
-    if (!IsWindows())
-      pthread_kill(parent, SIGUSR1);
+    pthread_kill(parent, SIGUSR1);
     usleep(1);
-    if (!IsWindows())
-      pthread_kill(parent, SIGUSR2);
+    pthread_kill(parent, SIGUSR2);
     usleep(1);
   }
   return 0;
@@ -100,8 +96,7 @@ TEST(getentropy, test) {
   }
   done = true;
   ASSERT_EQ(0, pthread_join(child, 0));
-  if (!IsWindows())
-    ASSERT_GT(gotsome, 0);
+  ASSERT_GT(gotsome, 0);
 }
 
 #endif /* __aarch64__ */