Fix possible segfault with 0x0 shared opcache base

bwoebi · bwoebi · commit 6fb8b9d721d0 · 2024-03-18T17:18:33.000+01:00
Moving the minimum base of the shared opcache memory to the second huge page to avoid a possible 0x0 base, which may cause all sorts of segfaults.
This is not a problem on most systems which have a mmap_min_addr which is non-zero, but e.g. WSL1 doesn't have a minimum mapping address.
diff --git a/ext/opcache/shared_alloc_mmap.c b/ext/opcache/shared_alloc_mmap.c
@@ -49,7 +49,7 @@
 static void *find_prefered_mmap_base(size_t requested_size)
 {
 	size_t huge_page_size = 2 * 1024 * 1024;
-	uintptr_t last_free_addr = 0;
+	uintptr_t last_free_addr = huge_page_size;
 	uintptr_t last_candidate = (uintptr_t)MAP_FAILED;
 	uintptr_t start, end, text_start = 0;
 #if defined(__linux__)

Original file line number	Diff line number	Diff line change
`@@ -49,7 +49,7 @@`
`49`	`49`	`static void *find_prefered_mmap_base(size_t requested_size)`
`50`	`50`	`{`
`51`	`51`	`size_t huge_page_size = 2 * 1024 * 1024;`
`52`		`- uintptr_t last_free_addr = 0;`
	`52`	`+ uintptr_t last_free_addr = huge_page_size;`
`53`	`53`	`uintptr_t last_candidate = (uintptr_t)MAP_FAILED;`
`54`	`54`	`uintptr_t start, end, text_start = 0;`
`55`	`55`	`#if defined(__linux__)`