On Tue, Apr 09, 2013 at 02:15:20AM +0200, Vladimir '??-coder/phcoder'
Serbinenko wrote:
> > === added directory 'grub-core/kern/arm/uboot'
> > === added file 'grub-core/kern/arm/uboot/startup.S'
> > --- grub-core/kern/arm/uboot/startup.S 1970-01-01 00:00:00 +0000
> > +++ grub-core/kern/arm/uboot/startup.S 2013-03-24 13:03:31 +0000
[...]
> > + @ Set up a new stack, beyond the end of copied modules.
> > + ldr r3, =GRUB_KERNEL_MACHINE_STACK_SIZE
> > + add r3, r1, r3 @ Place stack beyond end of modules
> > + and sp, r3, #~0x7 @ Ensure 8-byte alignment
> > +
> > + @ Since we _are_ the C run-time, we need to manually zero the BSS
> > + @ region before continuing
> > + bl uboot_get_real_bss_start @ zero from here
>
> This start is wrong. Even if modules start later due to alignment, BSS
> starts at __bss_start. Additional problem is that both __bss_start and
> _end may be unaligned unless special care is taken (like putting a dummy
> uint32_t at the beginning of BSS by putting it at the end of startup.S
> or using ld options)
My main concern here is getting the module start address right.
But see below.
> > + ldr r1, =EXT_C(_end) @ to here
> > + mov r2, #0
> > +1: str r2, [r0], #4
> > + cmp r0, r1
> > + bne 1b
> > +
> > + @ Global variables now accessible - store kernel parameters in memory
> > + ldr r12, =EXT_C(uboot_machine_type)
> > + str r4, [r12]
> > + ldr r12, =EXT_C(uboot_boot_data)
> > + str r5, [r12]
> > +
>
> Instead of temporary stashing the values to registers you can just init
> those values in C code to e.g. 0x55aa55aa so they'll be in .data and so
> accessible from the very beginning.
Neat :)
I'll do that.
> > + b EXT_C(grub_main)
> > +
> > + /*
> > + * __bss_start does not actually point to the start of the runtime
> > + * BSS, but rather to the next byte following the preceding data.
> > + */
>
> Only modules are aligned. BSS itself is still at _bss.
My issue with this statement is that this definition of BSS can
include padding before the first symbol inside the BSS.
I accept that it can also contain less-aligned symbols, which is a
problem that I need to handle in the code above.
> > +FUNCTION (uboot_get_real_bss_start)
> > + ldr r0, =EXT_C(__bss_start) @ src
> > + tst r0, #(GRUB_KERNEL_MACHINE_MOD_ALIGN - 1)
> > + beq 1f
> > + mvn r1, #(GRUB_KERNEL_MACHINE_MOD_ALIGN - 1)
> > + and r0, r0, r1
> > + add r0, r0, #(GRUB_KERNEL_MACHINE_MOD_ALIGN)
>
> Can be trivially simplified to:
> mvn r1, #(GRUB_KERNEL_MACHINE_MOD_ALIGN - 1)
> add r0, r0, r1
> and r0, r0, r1
Yes, I may have been a bit silly when writing the above (and now), but
I don't follow (0xfffffff8 + __bss_start) & 0xfffffff8 ?
Do you mean:
mvn r1, #(GRUB_KERNEL_MACHINE_MOD_ALIGN)
add r0, r0, #(GRUB_KERNEL_MACHINE_MOD_ALIGN - 1)
and r0, r0, r1
> which can be then inlined. Also it's more reliable to save grub_modbase
> as soon as we computed it in asm part (and use 0x55aa55aa trick to make
> it accessible early)
OK, that makes sense. And having done that, it can be inlined, since I no
longer need it from within uboot/init.c.
/
Leif
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