debug: msync only current page when validation frame pointer

This fixes lack of stack traces on arm64 macOS which were regressed
and not getting generated at all after this addition to write
current stack traces. Prior to this, function `isValidMemory` would
sync two subsequent pages if the aligned (base) address was different
than the frame pointer. I fail to see what the logic for such assumption
here is as the manual of `msync` clearly states it will fail with error
if the passed in memory region length contains unmapped regions.

This was the very reason why there were no stack traces print on
arm64 macOS as the second page was unmapped thus incorrectly flagging
the frame pointer as invalid.

1 files changed, 2 insertions, 7 deletions

diff --git a/lib/std/debug.zig b/lib/std/debug.zig
index 9b02d418c5..c50cdc2df8 100644
--- a/lib/std/debug.zig
+++ b/lib/std/debug.zig
@@ -429,11 +429,7 @@ pub const StackIterator = struct {
         if (native_os == .freestanding) return true;
 
         const aligned_address = address & ~@intCast(usize, (mem.page_size - 1));
-
-        // If the address does not span 2 pages, query only the first one
-        const length: usize = if (aligned_address == address) mem.page_size else 2 * mem.page_size;
-
-        const aligned_memory = @intToPtr([*]align(mem.page_size) u8, aligned_address)[0..length];
+        const aligned_memory = @intToPtr([*]align(mem.page_size) u8, aligned_address)[0..mem.page_size];
 
         if (native_os != .windows) {
             if (native_os != .wasi) {
@@ -451,11 +447,10 @@ pub const StackIterator = struct {
         } else {
             const w = os.windows;
             var memory_info: w.MEMORY_BASIC_INFORMATION = undefined;
-            //const memory_info_ptr = @ptrCast(w.PMEMORY_BASIC_INFORMATION, buffer);
 
             // The only error this function can throw is ERROR_INVALID_PARAMETER.
             // supply an address that invalid i'll be thrown.
-            const rc = w.VirtualQuery(aligned_memory.ptr, &memory_info, aligned_memory.len) catch {
+            const rc = w.VirtualQuery(aligned_memory, &memory_info, aligned_memory.len) catch {
                 return false;
             };