On 12.03.2013, at 12:51, Anton Blanchard wrote:
>
> Commit 5ac47f7a6efb (powerpc: Relocate prom_init.c on 64bit) made
> prom_init.c position independent by manually relocating its entries
> in the TOC.
>
> We get the address of the TOC entries with the __prom_init_toc_start
> linker symbol. If __prom_init_toc_start ends up as an entry in the
> TOC then we need to add an offset to get the current address. This is
> the case for older toolchains.
>
> On the other hand, if we have a newer toolchain that supports
> -mcmodel=medium then __prom_init_toc_start will be created by a
> relative offset from r2 (the TOC pointer). Since r2 has already been
> relocated, nothing more needs to be done. Adding an offset in this
> case is wrong and Aaro Koskinen and Alexander Graf have noticed noticed
> G5 and OpenBIOS breakage.
>
> Alan Modra suggested we just use r2 to get at the TOC which is simpler
> and works with both old and new toolchains.
>
> Reported-by: Alexander Graf <ag...@suse.de>
> Signed-off-by: Anton Blanchard <an...@samba.org>
This fixes my G5 again as well.
Acked-by: Alexander Graf <ag...@suse.de>
Please make sure this patch goes into 3.9.
Alex
> ---
>
> Thanks Aaro for reporting this, and Alexander for an initial
> fix. This tested ok for me with both a new and an old toolchain,
> but would appreciate if you could double check it fixes your issues
> too.
>
> diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
> index 7f7fb7f..13f8d16 100644
> --- a/arch/powerpc/kernel/prom_init.c
> +++ b/arch/powerpc/kernel/prom_init.c
> @@ -2832,11 +2832,13 @@ static void unreloc_toc(void)
> {
> }
> #else
> -static void __reloc_toc(void *tocstart, unsigned long offset,
> - unsigned long nr_entries)
> +static void __reloc_toc(unsigned long offset, unsigned long nr_entries)
> {
> unsigned long i;
> - unsigned long *toc_entry = (unsigned long *)tocstart;
> + unsigned long *toc_entry;
> +
> + /* Get the start of the TOC by using r2 directly. */
> + asm volatile("addi %0,2,-0x8000" : "=b" (toc_entry));
>
> for (i = 0; i < nr_entries; i++) {
> *toc_entry = *toc_entry + offset;
> @@ -2850,8 +2852,7 @@ static void reloc_toc(void)
> unsigned long nr_entries =
> (__prom_init_toc_end - __prom_init_toc_start) / sizeof(long);
>
> - /* Need to add offset to get at __prom_init_toc_start */
> - __reloc_toc(__prom_init_toc_start + offset, offset, nr_entries);
> + __reloc_toc(offset, nr_entries);
>
> mb();
> }
> @@ -2864,8 +2865,7 @@ static void unreloc_toc(void)
>
> mb();
>
> - /* __prom_init_toc_start has been relocated, no need to add offset */
> - __reloc_toc(__prom_init_toc_start, -offset, nr_entries);
> + __reloc_toc(-offset, nr_entries);
> }
> #endif
> #endif
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