Re: [LinuxBIOS] patch for making system run past disable_car

[Carl-Daniel Hailfinger]

On 11.12.2007 05:43, ron minnich wrote:
> note that the stage1_main code calls disable_car, then stage1_next.
> But disable_car calls stage1_next too! how
> can this works?
>
> The redundant call ensures this code works no
> matter whether the chip-dependent disable_car calls stage1_next or not.

I don't like this. disable_car() should just be able to return without
problems. If it can't do that, fix it.
Otherwise we have to document the call to stage1_end() as a requirement
of any diable_car() function and *justify* it.
> This change makes it possible for an lx to get through CAR to stage2.
>
> It's kind of ugly, but what it does is require the CAR code to call 
> a function, stage1_end. Why might this be needed? Because, at the end 
> of CAR, we invalidate the stack, which in turn *on some systems* will lose 
> the return address. We are thus losing our stack in disable_car, and 
> to compensate, we are jumping.

Why exactly do we invalidate the stack? If the stack is clobbered, the
contents of variables should be in a clobbered state as well. In that
case, I suspect parts of our v3 code would misbehave as well.

Can we make sure the stack contents are preserved?
> Signed-off-by: Ronald G. Minnich
> Index: arch/x86/stage1.c
>
> --- arch/x86/stage1.c	(revision 542)
> +++ arch/x86/stage1.c	(working copy)
> @@ -73,23 +73,12 @@
>   */
>  void __attribute__((stdcall)) stage1_main(u32 bist)
>  {
> void stage1_end(void);
> int ret;
> struct mem_file archive, result;
> struct mem_file archive;
> int elfboot_mem(struct lb_memory *mem, void *where, int size);
>
> void *entry;
>
> /* we can't statically init this hack. */
>
> unsigned char faker[64];
>
> struct lb_memory *mem = (struct lb_memory*) faker;
>
> mem->tag = LB_TAG_MEMORY;
>
> mem->size = 28;
>
> mem->map[0].start.lo = mem->map[0].start.hi = 0;
>
> mem->map[0].size.lo = (32*1024*1024);
>
> mem->map[0].size.hi = 0;
>
> mem->map[0].type = LB_MEM_RAM;
>
> post_code(0x02);
>
> // before we do anything, we want to stop if we dont run
>
> @@ -159,7 +148,27 @@
>
> /* Turn off Cache-As-Ram */
>    disable_car();
> stage1_end();
>
> +}
>
> +void stage1_end(void)
> +{
> int ret;
> struct mem_file archive, result;
> int elfboot_mem(struct lb_memory *mem, void *where, int size);
> void *entry;
> /* we can't statically init this hack. */
> unsigned char faker[64];
> struct lb_memory *mem = (struct lb_memory*) faker;
> mem->tag = LB_TAG_MEMORY;
> mem->size = 28;
> mem->map[0].start.lo = mem->map[0].start.hi = 0;
> mem->map[0].size.lo = (32*1024*1024);
> mem->map[0].size.hi = 0;
> mem->map[0].type = LB_MEM_RAM;
> entry = load_file_segments(&archive, "normal/stage2");
>  if (entry == (void *)-1)
>   die("FATAL: Failed loading stage2.");
> Index: arch/x86/geodelx/stage1.c
>
> --- arch/x86/geodelx/stage1.c	(revision 542)
> +++ arch/x86/geodelx/stage1.c	(working copy)
> @@ -55,9 +55,11 @@
>  void disable_car(void)
>  {
>    int i;
> void stage1_end(void);

If we really want to call stage1_end from disable_car(), we have to move
that to a header file.
> for (i = 0; i < ARRAY_SIZE(msr_table); i++)
>    	wrmsr(msr_table[i].msrnum, msr_table[i].msr);
>
> __asm__("wbinvd\n");
> stage1_end();

Disagreed, se above.
> }

Carl-Daniel