Re: [PATCH] MIPS: Allow compressed images to be loaded at the usual address

From: Jonas Gorski
Date: Thu Feb 09 2017 - 07:23:47 EST


Hi,

On 5 February 2017 at 21:21, Alban <albeu@xxxxxxx> wrote:
> From: Alban Bedel <albeu@xxxxxxx>
>
> Normally compressed images have to be loaded at a different address to
> allow the decompressor to run. This add an option to let vmlinuz copy
> itself to the correct address from the normal vmlinux address.
>
> Signed-off-by: Alban Bedel <albeu@xxxxxxx>
> ---
> arch/mips/Kconfig | 8 ++++++++
> arch/mips/boot/compressed/head.S | 13 +++++++++++++
> 2 files changed, 21 insertions(+)
>
> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> index b3c5bde..8074fc5 100644
> --- a/arch/mips/Kconfig
> +++ b/arch/mips/Kconfig
> @@ -2961,6 +2961,14 @@ choice
> bool "Extend builtin kernel arguments with bootloader arguments"
> endchoice
>
> +config ZBOOT_VMLINUZ_AT_VMLINUX_LOAD_ADDRESS
> + bool "Load compressed images at the same address as uncompressed"
> + depends on SYS_SUPPORTS_ZBOOT
> + help
> + vmlinux and vmlinuz normally have different load addresses, with
> + this option vmlinuz expect to be loaded at the same address as
> + vmlinux.
> +
> endmenu

Okay, it took me a while to understand the intention of this change. I
thought it was for supporting the case that VMLINUZ_LOAD_ADDRESS ==
VMLINUX_LOAD_ADDRESS, but it is indented for VMLINUZ_LOAD_ADDRESS !=
VMLINUX_LOAD_ADDRESS, but still being loaded at VMLINUX_LOAD_ADDRESS.

So I guess that this can only happen with vmlinuz.bin, as vmlinux's
ELF header will cause it to be loaded at the expected address (for
sane bootloaders at least).

> config LOCKDEP_SUPPORT
> diff --git a/arch/mips/boot/compressed/head.S b/arch/mips/boot/compressed/head.S
> index 409cb48..a215171 100644
> --- a/arch/mips/boot/compressed/head.S
> +++ b/arch/mips/boot/compressed/head.S
> @@ -25,6 +25,19 @@ start:
> move s2, a2
> move s3, a3
>
> +#ifdef CONFIG_ZBOOT_VMLINUZ_AT_VMLINUX_LOAD_ADDRESS

With a bit of BAL trickery you could easily detect this at runtime and
then conditionally copy without requiring any additional config
symbols. Then you aren't limited to being executed from
VMLINUX_LOAD_ADDRESS.

> + /* Move the text, data section and DTB to the correct address */
> + PTR_LA a0, .text
> + PTR_LI a1, VMLINUX_LOAD_ADDRESS
> + PTR_LA a2, _edata
> +0:
> + lw a3, 0(a1)
> + sw a3, 0(a0)
> + addiu a1, a1, 4
> + bne a2, a0, 0b
> + addiu a0, a0, 4
> +#endif
> +
> /* Clear BSS */
> PTR_LA a0, _edata
> PTR_LA a2, _end

Regards
Jonas