Messages in this thread Patches in this message | | | Date | Sat, 16 Feb 2013 00:14:49 -0500 (EST) | From | Nicolas Pitre <> | Subject | Re: [PATCH 8/9] [HACK] ARM: imx: work around v7_cpu_resume link error |
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On Fri, 15 Feb 2013, Russell King - ARM Linux wrote:
> On Thu, Feb 14, 2013 at 11:47:50PM +0100, Arnd Bergmann wrote: > > Patch c08e20d24 "arm: Add v7_invalidate_l1 to cache-v7.S" > > moves the v7_invalidate_l1 symbol out of imx/headsmp.S, > > which seems to cause a link error because it is now > > too far away from v7_cpu_resume when building an > > allyesconfig kernel. > > > > If we move the v7_cpu_resume function from the .data > > section to .text, that creates another link error > > for the reference to phys_l2x0_saved_regs, but we > > can move all of the above to .text. > > > > I believe that this is not a correct bug fix but just > > a bad workaround, so I'm open to ideas from people > > who understand the bigger picture. > > Unfortunately, this ends up with writable data in the .text section, which > is supposed to be read-only. We should try to preserve that status, even > though we don't enforce it. > > I guess the problem is that we end up with the .data segment soo far away > from the .text segment that these branches no longer work (and remember > that this code executes with the MMU off.) > > The only solution I can think is that we need to do quite a bit of magic > here to jump to an absolute address, but taking account of the V:P offset. > That's not going to be particularly nice, and it's going to then also have > to jump back the other way - to the cpu_resume code which is also in the > .data section.
Something like this should work:
diff --git a/arch/arm/mach-imx/headsmp.S b/arch/arm/mach-imx/headsmp.S index 7e49deb128..9de26f3edb 100644 --- a/arch/arm/mach-imx/headsmp.S +++ b/arch/arm/mach-imx/headsmp.S @@ -99,8 +99,11 @@ phys_l2x0_saved_regs: #endif ENTRY(v7_cpu_resume) - bl v7_invalidate_l1 + ldr ip, 2f + mov lr, pc +1: add pc, pc, ip pl310_resume b cpu_resume +2: .word v7_invalidate_l1 - 1b - 8 ENDPROC(v7_cpu_resume) #endif
However it is probably best to move all the code to the .text section where it belongs and fixup the data access instead. I must plead guilty for introducing this idea of putting code in the .data section with the SA1100resume code over 10 years ago that everyone copied since.
So here's how I think it should look instead, and how I should have done the SA1100 code back then:
diff --git a/arch/arm/mach-imx/headsmp.S b/arch/arm/mach-imx/headsmp.S index 7e49deb128..38a544a037 100644 --- a/arch/arm/mach-imx/headsmp.S +++ b/arch/arm/mach-imx/headsmp.S @@ -73,16 +73,16 @@ ENDPROC(v7_secondary_startup) #ifdef CONFIG_PM /* - * The following code is located into the .data section. This is to - * allow phys_l2x0_saved_regs to be accessed with a relative load - * as we are running on physical address here. + * The following code must assume it is running from physical address + * where absolute virtual addresses to the data section have to be + * turned into relative ones. */ - .data - .align #ifdef CONFIG_CACHE_L2X0 .macro pl310_resume - ldr r2, phys_l2x0_saved_regs + adr r0, phys_l2x0_saved_ptr_offset + ldr r2, [r0] + add r2, r2, r0 ldr r0, [r2, #L2X0_R_PHY_BASE] @ get physical base of l2x0 ldr r1, [r2, #L2X0_R_AUX_CTRL] @ get aux_ctrl value str r1, [r0, #L2X0_AUX_CTRL] @ restore aux_ctrl @@ -90,9 +90,13 @@ ENDPROC(v7_secondary_startup) str r1, [r0, #L2X0_CTRL] @ re-enable L2 .endm + .bss .globl phys_l2x0_saved_regs phys_l2x0_saved_regs: - .long 0 + .space 4 + .previous +phys_l2x0_saved_ptr_offset: + .word phys_l2x0_saved_regs - . #else .macro pl310_resume .endm And yet we could dispense with phys_l2x0_saved_regs altogether and use l2x0_saved_regs directly here instead.
That doesn't solve the issue of the kernel becoming too large for branch displacement fixup though.
Nicolas
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