Re: [OpenBIOS] [PATCH 2/4] ppc: add new context handler

[Segher Boessenkool]

On Sun, May 01, 2016 at 11:23:00AM +0100, Mark Cave-Ayland wrote:
> +struct context *switch_to(struct context *ctx)
> +{
> volatile struct context *save;
> struct context *ret;
> unsigned int lr;
> debug("switching to new context:\n");
> save = __context;
> __context = ctx;
> asm __volatile__ ("mflr %0\n\t" : "=r" (lr) : : );
> asm __volatile__ ("bl __switch_context\n");
> asm __volatile__ ("mtlr %0\n\t" : : "r" (lr) : );
> ret = __context;
> __context = (struct context *)save;
> return ret;
>
> +}

This isn't correct; GCC is free to put LR-modifying code between
the asm statements.  You should do it in one asm statement.
> #ifdef __powerpc64__
> #define ULONG_SIZE 8
> #define STACKFRAME_MINSIZE 48

The miminum frame size for elfv1 is 112 and for elfv2 is 32.  I think.
But not 48, in any case.

Segher