[PATCH v3] ARM: xip: Use correct symbol for end of ROM marker

[Nicolas Pitre]

On Mon, 16 Nov 2015, Chris Brandt wrote:

> For an XIP build, _edata_loc, not _etext, represents the end of the
> binary image that will be programmed into ROM and mapped into the
> MODULES_VADDR area.

This statement is wrong.  The kernel data is copied to RAM before the 
MMU is turned on and that's the copy that the kernel must use.  There is 
no reason having anything past _etext accessible from ROM.

> With an XIP kernel, nothing is loaded into RAM before boot, meaning
> you have to take into account the size of the entire binary image
> that was programmed, including the init data values that will be copied
> to RAM during kernel boot.

But this is done way before the code you're modifying is executed.

> This fixes the bug where you might lose the end of your kernel area
> after page table setup is complete.

Could you elaborate about a possible bug please?

> Signed-off-by: Chris Brandt <chris.brandt at renesas.com>
> ---
> v3:
> * Removed sections.h from Kbuild
> v2:
> * Added change for MODULES_VADDR
> * Moved extern to new file asm/sections.h
> ---
>  arch/arm/include/asm/Kbuild     |    1 -
>  arch/arm/include/asm/sections.h |    8 ++++++++
>  arch/arm/kernel/module.c        |    2 +-
>  arch/arm/mm/mmu.c               |    4 ++--
>  4 files changed, 11 insertions(+), 4 deletions(-)
>  create mode 100644 arch/arm/include/asm/sections.h
> 
> diff --git a/arch/arm/include/asm/Kbuild b/arch/arm/include/asm/Kbuild
> index be648eb..6d3da22 100644
> --- a/arch/arm/include/asm/Kbuild
> +++ b/arch/arm/include/asm/Kbuild
> @@ -21,7 +21,6 @@ generic-y += preempt.h
>  generic-y += resource.h
>  generic-y += rwsem.h
>  generic-y += seccomp.h
> -generic-y += sections.h
>  generic-y += segment.h
>  generic-y += sembuf.h
>  generic-y += serial.h
> diff --git a/arch/arm/include/asm/sections.h b/arch/arm/include/asm/sections.h
> new file mode 100644
> index 0000000..401eb3c2
> --- /dev/null
> +++ b/arch/arm/include/asm/sections.h
> @@ -0,0 +1,8 @@
> +#ifndef _ASM_ARM_SECTIONS_H
> +#define _ASM_ARM_SECTIONS_H
> +
> +#include <asm-generic/sections.h>
> +
> +extern char _edata_loc[];
> +
> +#endif	/* _ASM_ARM_SECTIONS_H */
> diff --git a/arch/arm/kernel/module.c b/arch/arm/kernel/module.c
> index efdddcb..41ae2cc 100644
> --- a/arch/arm/kernel/module.c
> +++ b/arch/arm/kernel/module.c
> @@ -34,7 +34,7 @@
>   * recompiling the whole kernel when CONFIG_XIP_KERNEL is turned on/off.
>   */
>  #undef MODULES_VADDR
> -#define MODULES_VADDR	(((unsigned long)_etext + ~PMD_MASK) & PMD_MASK)
> +#define MODULES_VADDR	(((unsigned long)_edata_loc + ~PMD_MASK) & PMD_MASK)
>  #endif
>  
>  #ifdef CONFIG_MMU
> diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
> index 4867f5d..dd5a56b 100644
> --- a/arch/arm/mm/mmu.c
> +++ b/arch/arm/mm/mmu.c
> @@ -1210,7 +1210,7 @@ static inline void prepare_page_table(void)
>  
>  #ifdef CONFIG_XIP_KERNEL
>  	/* The XIP kernel is mapped in the module area -- skip over it */
> -	addr = ((unsigned long)_etext + PMD_SIZE - 1) & PMD_MASK;
> +	addr = ((unsigned long)_edata_loc + PMD_SIZE - 1) & PMD_MASK;
>  #endif
>  	for ( ; addr < PAGE_OFFSET; addr += PMD_SIZE)
>  		pmd_clear(pmd_off_k(addr));
> @@ -1292,7 +1292,7 @@ static void __init devicemaps_init(const struct machine_desc *mdesc)
>  #ifdef CONFIG_XIP_KERNEL
>  	map.pfn = __phys_to_pfn(CONFIG_XIP_PHYS_ADDR & SECTION_MASK);
>  	map.virtual = MODULES_VADDR;
> -	map.length = ((unsigned long)_etext - map.virtual + ~SECTION_MASK) & SECTION_MASK;
> +	map.length = ((unsigned long)_edata_loc - map.virtual + ~SECTION_MASK) & SECTION_MASK;
>  	map.type = MT_ROM;
>  	create_mapping(&map);
>  #endif
> -- 
> 1.7.9.5
> 
> 
> 
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