077925e2b0
Prior to regabi, the compiler passed defer arguments to the runtime as untyped values on the stack. This meant a lot of defer-related runtime functions had to be very careful not to grow the stack or allow preemption since the stack could not be safely scanned or moved. However, with regabi, every defer is now simply a func() from the runtime's perspective, which means we no longer have untyped values on the stack when we enter defer-related runtime code. Hence, this CL removes a lot of the now-unnecessary carefulness in the defer implementation. Specifically, deferreturn no longer needs to be nosplit because it doesn't copy untyped defer arguments to its caller's frame (we also update some stale comments in deferreturn). freedefer no longer needs to be nosplit because it's none of its callers are deeply nosplit. And newdefer and freedefer no longer need to switch to the systemstack on their slow paths to avoid stack growth. deferprocStack is the only function that still needs to be nosplit, but that's because the compiler calls it with uninitialized live pointer slots on the stack (maybe we should change that, but that's a very different fix). This is a retry of CL 337651, which was rolled back. This version disables preemption in newdefer and freedefer while they hold the current P. Change-Id: Ibf469addc0b69dc3ba9a3d1a5e0c2804b7b4b244 Reviewed-on: https://go-review.googlesource.com/c/go/+/339396 Trust: Austin Clements <austin@google.com> Run-TryBot: Austin Clements <austin@google.com> TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Cherry Mui <cherryyz@google.com> |
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