On 18 November 2012 21:52, Robert P. J. Day <rpjday@xxxxxxxxxxxxxx> wrote:
>
> perusing the code to see how the final barebox executable is created
> and ran across this opening to include/asm-generic/barebox.lds.h:
>
> #if defined CONFIG_ARCH_IMX25 || \
> defined CONFIG_ARCH_IMX35 || \
> defined CONFIG_ARCH_IMX51 || \
> defined CONFIG_ARCH_IMX53 || \
> defined CONFIG_ARCH_IMX6 || \
> defined CONFIG_X86 || \
> defined CONFIG_ARCH_EP93XX
> #include <mach/barebox.lds.h>
> #endif
>
> #ifndef PRE_IMAGE
> #define PRE_IMAGE
> #endif
>
> i find that more than a little confusing and inappropriate -- it
> strikes me that the allegedly "generic" lds.h file shouldn't be
> testing for an arbitrary set of inexplicable machine/arch
> combinations, especially when there is absolutely no explanation about
> what makes that particular set of symbols magic with respect to this
> file.
>
> a minute or two of perusing shows that what it's for is inserting
> some special "pre-image" content into the executable, but that means
> that for each new selection that needs that, this file will have to be
> changed and that's just messy.
>
> the linux kernel has a simpler strategy for
> asm-generic/vmlinux.lds.h, as you see in this patch snippet that added
> bss first section functionality to that file earlier this year:
>
> +/*
> + * Allow archectures to redefine BSS_FIRST_SECTIONS to add extra
> + * sections to the front of bss.
> + */
> +#ifndef BSS_FIRST_SECTIONS
> +#define BSS_FIRST_SECTIONS
> +#endif
> +
> #define BSS(bss_align) \
> . = ALIGN(bss_align); \
> .bss : AT(ADDR(.bss) - LOAD_OFFSET) { \
> + BSS_FIRST_SECTIONS \
> *(.bss..page_aligned) \
> *(.dynbss) \
> *(.bss) \
>
> that would seem to be a much nicer solution as it pushes the
> selection of pre-image content back to the architectures where it
> belongs.
>
> the fact that the current approach is prone to "error" can be seen
> in the file arch/mips/lib/barebox.lds.S:
>
> #include <asm-generic/barebox.lds.h>
>
> OUTPUT_ARCH(mips)
> ENTRY(_start)
> SECTIONS
> {
> . = TEXT_BASE;
>
> . = ALIGN(4);
> .text :
> {
> _start = .;
> *(.text_entry*)
> _stext = .;
> _text = .;
> __bare_init_start = .;
> *(.text_bare_init*)
> __bare_init_end = .;
> *(.text*)
> }
> BAREBOX_BARE_INIT_SIZE
>
> PRE_IMAGE <--- ?????
>
> apparently, the MIPS architecture is including the "PRE_IMAGE"
> content, despite the fact that it can't possibly be defined. it's not
> wrong, it's just pointless and potentially confusing.
Unfortunately nowadays MIPS lacks lowlevel initialization support.
Yesterday I mailed RFC about pbl (prebootloader) support. It needs
much work, but IMHO after incorporating MIPS pbl support the status of
"PRE_IMAGE" will be more clear.
--
Best regards,
Antony Pavlov
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