std.debug.cpu_context.Sparc: flush register windows in current()

It's better to do this here than in StackIterator.init() so that
std.debug.cpu_context.Native.current() isn't a footgun on SPARC.

1 files changed, 11 insertions, 0 deletions

diff --git a/lib/std/debug/cpu_context.zig b/lib/std/debug/cpu_context.zig
index 3450debba0..5dd2e283ed 100644
--- a/lib/std/debug/cpu_context.zig
+++ b/lib/std/debug/cpu_context.zig
@@ -870,6 +870,8 @@ const Sparc = extern struct {
     pub const Gpr = if (native_arch == .sparc64) u64 else u32;
 
     pub inline fn current() Sparc {
+        flushWindows();
+
         var ctx: Sparc = undefined;
         asm volatile (if (Gpr == u64)
                 \\ stx %g0, [%l0 + 0]
@@ -933,6 +935,15 @@ const Sparc = extern struct {
         return ctx;
     }
 
+    noinline fn flushWindows() 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
+    }
+
     pub fn dwarfRegisterBytes(ctx: *Sparc, register_num: u16) DwarfRegisterError![]u8 {
         switch (register_num) {
             0...7 => return @ptrCast(&ctx.g[register_num]),