Hi Nicolas,
On Wed, Aug 30, 2017 at 4:55 AM, Nicolas Pitre <nicolas.pitre@xxxxxxxxxx> wrote:
> Let's use optimized routines such as memcpy to copy .data and memzero
> to clear .bss in the startup code instead of doing it one word at a
> time. Those routines don't use any global data so they're safe to use
> even if .data and .bss segments are not initialized.
>
> In the .data copy case a temporary stack is installed in the .bss area
> as the actual kernel stack is located within the copied data area. The
> XIP kernel linker script ensures a 8 byte alignment for that purpose.
>
> Finally, make the .data copy and related pointers surrounded by
> CONFIG_XIP_KERNEL to make it obvious what it is all about. This will
> allow for further cleanups in the non-XIP linker script.
>
> Signed-off-by: Nicolas Pitre <nico@xxxxxxxxxx>
> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
This is now commit 9520b1a1b5f7a348 ("ARM: head-common.S: speed up startup
code") in arm/for-next.
If CONFIG_DEBUG_LOCK_ALLOC=y, the kernel log is spammed with a few hundred
identical messages on various Renesas systems:
unwind: Unknown symbol address c0800300
unwind: Index not found c0800300
I've bisected this to the aforementioned commit.
c0800300 points to the instruction just after the __memzero call, cfr. below.
Do you have a clue? Thanks!
> --- a/arch/arm/kernel/head-common.S
> +++ b/arch/arm/kernel/head-common.S
> @@ -79,47 +79,59 @@ ENDPROC(__vet_atags)
> */
> __INIT
> __mmap_switched:
> - adr r3, __mmap_switched_data
> -
> - ldmia r3!, {r4, r5, r6, r7}
> - cmp r4, r5 @ Copy data segment if needed
> -1: cmpne r5, r6
> - ldrne fp, [r4], #4
> - strne fp, [r5], #4
> - bne 1b
> -
> - mov fp, #0 @ Clear BSS (and zero fp)
> -1: cmp r6, r7
> - strcc fp, [r6],#4
> - bcc 1b
> -
> - ARM( ldmia r3, {r4, r5, r6, r7, sp})
> - THUMB( ldmia r3, {r4, r5, r6, r7} )
> - THUMB( ldr sp, [r3, #16] )
> - str r9, [r4] @ Save processor ID
> - str r1, [r5] @ Save machine type
> - str r2, [r6] @ Save atags pointer
> - cmp r7, #0
> - strne r0, [r7] @ Save control register values
> +
> + mov r7, r1
> + mov r8, r2
> + mov r10, r0
> +
> + adr r4, __mmap_switched_data
> + mov fp, #0
> +
> +#ifdef CONFIG_XIP_KERNEL
> + ARM( ldmia r4!, {r0, r1, r2, sp} )
> + THUMB( ldmia r4!, {r0, r1, r2, r3} )
> + THUMB( mov sp, r3 )
> + sub r2, r2, r1
> + bl memcpy @ copy .data to RAM
> +#endif
> +
> + ARM( ldmia r4!, {r0, r1, sp} )
> + THUMB( ldmia r4!, {r0, r1, r3} )
> + THUMB( mov sp, r3 )
> + sub r1, r1, r0
> + bl __memzero @ clear .bss
> +
c0800300 is the address of the next instruction:
> + ldmia r4, {r0, r1, r2, r3}
> + str r9, [r0] @ Save processor ID
> + str r7, [r1] @ Save machine type
> + str r8, [r2] @ Save atags pointer
> + cmp r3, #0
> + strne r10, [r3] @ Save control register values
> b start_kernel
> ENDPROC(__mmap_switched)
>
> .align 2
> .type __mmap_switched_data, %object
> __mmap_switched_data:
> - .long __data_loc @ r4
> - .long _sdata @ r5
> - .long __bss_start @ r6
> - .long _end @ r7
> - .long processor_id @ r4
> - .long __machine_arch_type @ r5
> - .long __atags_pointer @ r6
> +#ifdef CONFIG_XIP_KERNEL
> + .long _sdata @ r0
> + .long __data_loc @ r1
> + .long _edata_loc @ r2
> + .long __bss_stop @ sp (temporary stack in .bss)
> +#endif
> +
> + .long __bss_start @ r0
> + .long __bss_stop @ r1
> + .long init_thread_union + THREAD_START_SP @ sp
> +
> + .long processor_id @ r0
> + .long __machine_arch_type @ r1
> + .long __atags_pointer @ r2
> #ifdef CONFIG_CPU_CP15
> - .long cr_alignment @ r7
> + .long cr_alignment @ r3
> #else
> - .long 0 @ r7
> + .long 0 @ r3
> #endif
> - .long init_thread_union + THREAD_START_SP @ sp
> .size __mmap_switched_data, . - __mmap_switched_data
>
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
