std.debug: flush SPARC register windows from a new window

flushw and ta 3 flush all windows *except* the current one. So we need to do
this in a new register window to get all of the ones we care about.

1 files changed, 10 insertions, 8 deletions

diff --git a/lib/std/debug.zig b/lib/std/debug.zig
index 7ac6c45903..3f694bec1c 100644
--- a/lib/std/debug.zig
+++ b/lib/std/debug.zig
@@ -807,14 +807,7 @@ const StackIterator = union(enum) {
     /// `@frameAddress` and `cpu_context.Native.current` as the caller's stack frame and
     /// our own are one and the same.
     inline fn init(opt_context_ptr: ?CpuContextPtr) error{CannotUnwindFromContext}!StackIterator {
-        if (builtin.cpu.arch.isSPARC()) {
-            // Flush all the register windows on stack.
-            if (builtin.cpu.has(.sparc, .v9)) {
-                asm volatile ("flushw" ::: .{ .memory = true });
-            } else {
-                asm volatile ("ta 3" ::: .{ .memory = true }); // ST_FLUSH_WINDOWS
-            }
-        }
+        flushSparcWindows();
         if (opt_context_ptr) |context_ptr| {
             if (SelfInfo == void or !SelfInfo.can_unwind) return error.CannotUnwindFromContext;
             // Use `di_first` here so we report the PC in the context before unwinding any further.
@@ -842,6 +835,15 @@ const StackIterator = union(enum) {
         }
     }
 
+    noinline fn flushSparcWindows() void {
+        // Flush all register windows except the current one (hence `noinline`). This ensures that
+        // we actually see meaningful data on the stack when we walk the frame chain.
+        if (comptime builtin.target.cpu.has(.sparc, .v9))
+            asm volatile ("flushw" ::: .{ .memory = true })
+        else
+            asm volatile ("ta 3" ::: .{ .memory = true }); // ST_FLUSH_WINDOWS
+    }
+
     const FpUsability = enum {
         /// FP unwinding is impractical on this target. For example, due to its very silly ABI
         /// design decisions, it's not possible to do generic FP unwinding on MIPS without a