Re: [PATCH 2/2] MIPS: mm: Use scratch for PGD when !CONFIG_MIPS_PGD_C0_CONTEXT

[Ralf Baechle <ralf@linux-mips.org>]

On Sun, Aug 11, 2013 at 05:10:17PM +0530, Jayachandran C wrote:

> Allow usage of scratch register for current pgd even when
> MIPS_PGD_C0_CONTEXT is not configured. MIPS_PGD_C0_CONTEXT is set
> for 64r2 platforms to indicate availability of Xcontext for saving
> cpuid, thus freeing Context to be used for saving PGD. This option
> was also tied to using a scratch register for storing PGD.
> 
> This commit will allow usage of scratch register to store the current
> pgd if one can be allocated for the platform, even when
> MIPS_PGD_C0_CONTEXT is not set. The cpuid will be kept in the CP0
> Context register in this case.
> 
> The code to store the current pgd for the TLB miss handler is now
> generated in all cases. When scratch register is available, the PGD
> is also stored in the scratch register.

This patch breaks the build for almost all platforms.  Amusingly it
doesn't break Cavium however which is why I didn't notice it right away.

The build error is the same for all platforms:

[...]
  LD      init/built-in.o
arch/mips/built-in.o: In function `per_cpu_trap_init':
(.text+0x80e4): undefined reference to `tlbmiss_handler_setup_pgd'
arch/mips/built-in.o: In function `build_setup_pgd':
tlbex.c:(.text+0xe31c): undefined reference to `tlbmiss_handler_setup_pgd'
tlbex.c:(.text+0xe328): undefined reference to `tlbmiss_handler_setup_pgd'
tlbex.c:(.text+0xe324): undefined reference to `tlbmiss_handler_setup_pgd_end'
tlbex.c:(.text+0xe32c): undefined reference to `tlbmiss_handler_setup_pgd_end'
kernel/built-in.o: In function `__schedule':
core.c:(.sched.text+0x1b74): undefined reference to `tlbmiss_handler_setup_pgd'
mm/built-in.o: In function `use_mm':
(.text+0x1a530): undefined reference to `tlbmiss_handler_setup_pgd'
fs/built-in.o: In function `flush_old_exec':
(.text+0x8da8): undefined reference to `tlbmiss_handler_setup_pgd'
make[2]: *** [vmlinux] Error 1
make[1]: *** [sub-make] Error 2
make: *** [all] Error 2
make: Leaving directory `/home/ralf/src/linux/obj/cobalt-build'

I'm reverting the patch now.

  Ralf