Re: [PATCH 2/4] coroutine: Add check for SafeStack in sigalstack

[Stefan Hajnoczi]

On Wed, Apr 29, 2020 at 03:44:18PM -0400, Daniele Buono wrote:

s/sigalstack/sigaltstack/ in the commit message.

> LLVM's SafeStack instrumentation cannot be used inside signal handlers
> that make use of sigaltstack().
> Since coroutine-sigaltstack relies on sigaltstack(), it is not
> compatible with SafeStack. The resulting binary is incorrect, with
> different coroutines sharing the same unsafe stack and producing
> undefined behavior at runtime.
> To avoid this, we add a check in coroutine-sigaltstack that throws a
> preprocessor #error and interrupt the compilation if SafeStack is
> enabled.
> 
> Signed-off-by: Daniele Buono <address@hidden>
> ---
>  util/coroutine-sigaltstack.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/util/coroutine-sigaltstack.c b/util/coroutine-sigaltstack.c
> index f6fc49a0e5..b7cdc959f8 100644
> --- a/util/coroutine-sigaltstack.c
> +++ b/util/coroutine-sigaltstack.c
> @@ -30,6 +30,10 @@
>  #include "qemu-common.h"
>  #include "qemu/coroutine_int.h"
>  
> +#ifdef CONFIG_SAFESTACK
> +#error "SafeStack does not work with sigaltstack's implementation"
> +#endif

Neither the commit description nor the #error message explain why it
doesn't work. Could it work in the future or is there a fundamental
reason why it will never work?

Stefan

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