RE: [PATCH] Hexagon: Swap SIGRGMAX-1 and SIGRTMIN+1

[Taylor Simpson]

Peter,

Yeah, I was surprised not to see other targets encountering this problem.  
However, I don't understand how something under #ifdef TARGET_HEXAGON can break 
anything else.

Could you point me to the patch set you mention?

One generic solution I can think of is to reference a target-defined macro in 
linux-user/signal.c and let targets optionally define it in their 
target_signal.h.  So, it would look something like this
> @@ -72,6 +72,14 @@ static uint8_t host_to_target_signal_table[_NSIG] = {
>         over a single host signal.  */
>      [__SIGRTMIN] = __SIGRTMAX,
>      [__SIGRTMAX] = __SIGRTMIN,
> +#ifdef TARGET_SIGNAL_TABLE_MODIFY
> +    TARGET_SIGNAL_TABLE_MODIFY

Thanks,
Taylor


-----Original Message-----
From: Peter Maydell <address@hidden>
Sent: Tuesday, November 19, 2019 1:31 PM
To: Taylor Simpson <address@hidden>
Cc: Riku Voipio <address@hidden>; Laurent Vivier <address@hidden>; QEMU 
Developers <address@hidden>
Subject: Re: [PATCH] Hexagon: Swap SIGRGMAX-1 and SIGRTMIN+1


On Tue, 19 Nov 2019 at 19:07, Taylor Simpson <address@hidden> wrote:
>
> Signed-off-by: Taylor Simpson <address@hidden>
> ---
>  linux-user/signal.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/linux-user/signal.c b/linux-user/signal.c index
> 5ca6d62..ce3d27f 100644
> --- a/linux-user/signal.c
> +++ b/linux-user/signal.c
> @@ -72,6 +72,14 @@ static uint8_t host_to_target_signal_table[_NSIG] = {
>         over a single host signal.  */
>      [__SIGRTMIN] = __SIGRTMAX,
>      [__SIGRTMAX] = __SIGRTMIN,
> +#ifdef TARGET_HEXAGON
> +    /*
> +     * Hexagon uses the same signal for pthread cancel as the host pthreads,
> +     * so cannot be overridden.
> +     * Therefore, we map Hexagon signal to a different host signal.
> +     */
> +    [__SIGRTMAX - 1] = __SIGRTMIN + 1, #endif
>  };

This breaks other stuff, unfortunately, like Go binaries.
(Also, you now have two host signals mapped to the same target signal; notice 
that the existing RTMAX/RTMIN is a swap of the two slots.)

We need a generic solution for this, Hexagon is not the only one with the 
problem. There's a patchset on list from ages back that had a suggested 
approach, but it needed review and work.

thanks
-- PMM