os: drop unnecessary memcpy in wl_os_mremap_maymove

FreeBSD doesn't support mremap [1], so we have a fallback
implementation based on munmap+mmap. We memcpy from the old memory
region to the new one, however this is unnecessary because the new
mapping references the same file as the old one.

Use msync to make sure any pending write is flushed to the underlying
file before we map the new region.

[1]: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=59912

Signed-off-by: Simon Ser <contact@emersion.fr>

1 files changed, 13 insertions, 12 deletions

diff --git a/src/wayland-os.c b/src/wayland-os.c
index 27c6035..a9066ca 100644
--- a/src/wayland-os.c
+++ b/src/wayland-os.c
@@ -231,21 +231,22 @@ wl_os_mremap_maymove(int fd, void *old_data, ssize_t *old_size,
 		     ssize_t new_size, int prot, int flags)
 {
 	void *result;
-	/*
-	 * We could try mapping a new block immediately after the current one
+
+	/* Make sure any pending write is flushed. */
+	if (msync(old_data, *old_size, MS_SYNC) != 0)
+		return MAP_FAILED;
+
+	/* We could try mapping a new block immediately after the current one
 	 * with MAP_FIXED, however that is not guaranteed to work and breaks
 	 * on CHERI-enabled architectures since the data pointer will still
-	 * have the bounds of the previous allocation. As this is not a
-	 * performance-critical path, we always map a new region and copy the
-	 * old data to the new region.
+	 * have the bounds of the previous allocation.
 	 */
 	result = mmap(NULL, new_size, prot, flags, fd, 0);
-	if (result != MAP_FAILED) {
-		/* Copy the data over and unmap the old mapping. */
-		memcpy(result, old_data, *old_size);
-		if (munmap(old_data, *old_size) == 0) {
-			*old_size = 0; /* successfully unmapped old data. */
-		}
-	}
+	if (result == MAP_FAILED)
+		return MAP_FAILED;
+
+	if (munmap(old_data, *old_size) == 0)
+		*old_size = 0;
+
 	return result;
 }