Messages in this thread | | | Date | Sat, 22 Sep 2012 11:10:57 -0400 (EDT) | From | Nicolas Pitre <> | Subject | Re: [PATCH v3 RESEND 01/17] ARM: add mechanism for late code patching |
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On Fri, 21 Sep 2012, Cyril Chemparathy wrote:
> The original phys_to_virt/virt_to_phys patching implementation relied on early > patching prior to MMU initialization. On PAE systems running out of >4G > address space, this would have entailed an additional round of patching after > switching over to the high address space. > > The approach implemented here conceptually extends the original PHYS_OFFSET > patching implementation with the introduction of "early" patch stubs. Early > patch code is required to be functional out of the box, even before the patch > is applied. This is implemented by inserting functional (but inefficient) > load code into the .runtime.patch.code init section. Having functional code > out of the box then allows us to defer the init time patch application until > later in the init sequence. > > In addition to fitting better with our need for physical address-space > switch-over, this implementation should be somewhat more extensible by virtue > of its more readable (and hackable) C implementation. This should prove > useful for other similar init time specialization needs, especially in light > of our multi-platform kernel initiative. > > This code has been boot tested in both ARM and Thumb-2 modes on an ARMv7 > (Cortex-A8) device. > > Note: the obtuse use of stringified symbols in patch_stub() and > early_patch_stub() is intentional. Theoretically this should have been > accomplished with formal operands passed into the asm block, but this requires > the use of the 'c' modifier for instantiating the long (e.g. .long %c0). > However, the 'c' modifier has been found to ICE certain versions of GCC, and > therefore we resort to stringified symbols here. > > Signed-off-by: Cyril Chemparathy <cyril@ti.com> > Reviewed-by: Nicolas Pitre <nico@linaro.org>
There is another problem with this.
[...] > diff --git a/arch/arm/include/asm/runtime-patch.h b/arch/arm/include/asm/runtime-patch.h > new file mode 100644 > index 0000000..366444d > --- /dev/null > +++ b/arch/arm/include/asm/runtime-patch.h > @@ -0,0 +1,208 @@ > +/* > + * arch/arm/include/asm/runtime-patch.h > + * Note: this file should not be included by non-asm/.h files > + * > + * Copyright 2012 Texas Instruments, Inc. > + * > + * This program is free software; you can redistribute it and/or modify it > + * under the terms and conditions of the GNU General Public License, > + * version 2, as published by the Free Software Foundation. > + * > + * This program is distributed in the hope it will be useful, but WITHOUT > + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or > + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for > + * more details. > + * > + * You should have received a copy of the GNU General Public License along with > + * this program. If not, see <http://www.gnu.org/licenses/>. > + */ > +#ifndef __ASM_ARM_RUNTIME_PATCH_H > +#define __ASM_ARM_RUNTIME_PATCH_H > + > +#include <linux/stringify.h> > + > +#ifndef __ASSEMBLY__ > + > +#ifdef CONFIG_ARM_RUNTIME_PATCH > + > +struct patch_info { > + void *insn; > + u16 type; > + u8 insn_size; > + u8 data_size; > + u32 data[0]; > +};
This causes the following compilation error:
CC sound/core/pcm.o In file included from sound/core/pcm.c:293:0: include/linux/soundcard.h:223:8: error: redefinition of 'struct patch_info' arch/arm/include/asm/runtime-patch.h:28:8: note: originally defined here make[2]: *** [sound/core/pcm.o] Error 1
The problem is that asm/runtime-patch.h gets included by asm/memory.h and asm/memory.h is included by almost the entire kernel. Something like "struct patch_info" is a bit too generic a name to be exported to the world as the likelihood of a name collision with some private definition in a driver or the like is rather high.
In that context it might be worth moving everything that is not required for the patch stub definitions out of asm/runtime-patch.h. For example, the definition of struct patch_info, struct patch_info_imm8, patch_next() and patch_data() could be moved to runtime-patch.c directly instead. And then patch_stub() should be renamed to runtime_patch_stub(), early_patch_stub() to early_runtime_patch_stub(), patch_imm8() to runtime_patch_imm8(), etc. Even the __IMM8 symbol name is rather weak for kernel wide scope.
Nicolas
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