Re: [PATCH] plugin: fix clearing of plugin_mem_cbs before TB exit

[Richard Henderson <richard.henderson@linaro.org>]

On 2/21/23 18:32, Emilio Cota wrote:
> Currently we are wrongly accessing plugin_tb->mem_helper at
> translation time from plugin_gen_disable_mem_helpers, which is
> called before generating a TB exit, e.g. with exit_tb.
> 
> Recall that it is only during TB finalisation, i.e. when we go over
> the TB post-translation to inject or remove plugin instrumentation,
> when plugin_tb->mem_helper is set. This means that we never clear
> plugin_mem_cbs when calling plugin_gen_disable_mem_helpers since
> mem_helper is always false. Therefore a guest instruction that uses
> helpers and emits an explicit TB exit results in plugin_mem_cbs being
> set upon exiting, which is caught by an assertion as reported in
> the reopening of issue #1381 and replicated below.
> 
> Fix this by (1) adding an insertion point before exiting a TB
> ("before_exit"), and (2) deciding whether or not to emit the
> clearing of plugin_mem_cbs at this newly-added insertion point
> during TB finalisation.

This is an improvement, but incomplete, because it does not handle the exception exit 
case, via cpu_loop_exit.


r~