Re: [musl] sigsetjmp

[Rich Felker <dalias@libc.org>]

On Sun, Jun 07, 2020 at 08:45:11PM -0500, sidneym@codeaurora.org wrote:
> Wanting to make sure I'm reading the requirements correctly.
> 
> Looks like this routine only needs to save the link register and env, call
> setjmp then restore the link register and env followed by the tail call.

Yes, that's correct. This is an unconventional design but necessary so
that the stack frame has already been restored when signals are
unmasked by siglongjmp. See the message for commit
583e55122e767b1586286a0d9c35e2a4027998ab for a description of how this
works.

> Hexagon was out of date so I did this:
> 
>  
> 
> ..balign 4
> 
> ..type sigsetjmp,@function
> 
> sigsetjmp:
> 
>         // if savemask is 0 sigsetjmp behaves like setjmp
> 
>         {
> 
>                 p0 = cmp.eq(r1, #0)
> 
>                 if (p0.new) jump:t ##setjmp
> 
>         }
> 
>         {   
> 
>                 memw(r0+#64+4) = r16  // save r16 in __ss[0]
> 
>                 memw(r0+#64)   = r31  // save linkregister in __fl
> 
>                 r16 = r0
> 
>         }   

This is not correct. __ss[0] is occupied by the saved signal mask, and
will be clobbered when it's saved in the tail call. Instead you need
to use unused space in struct __jmp_buf_tag. The canonical place is
(char*)__ss+8 (the "HURD ABI area" :) assuming _NSIG==65.

Rich