[PATCH v4] efi: arm64: Add vmlinux debug link to the Image binary

[Will Deacon]

Hi Ard,

On Thu, Feb 02, 2017 at 05:33:19PM +0000, Ard Biesheuvel wrote:
> When building with debugging symbols, take the absolute path to the
> vmlinux binary and add it to the special PE/COFF debug table entry.
> This allows a debug EFI build to find the vmlinux binary, which is
> very helpful in debugging, given that the offset where the Image is
> first loaded by EFI is highly unpredictable.
> 
> On implementations of UEFI that choose to implement it, this
> information is exposed via the EFI debug support table, which is a UEFI
> configuration table that is accessible both by the firmware at boot time
> and by the OS at runtime, and lists all PE/COFF images loaded by the
> system.
> 
> The format of the NB10 Codeview entry is based on the definition used
> by EDK2, which is our primary reference when it comes to the use of
> PE/COFF in the context of UEFI firmware.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> ---
> v4: add a separate DEBUG_EFI debug option so that this feature is disabled
>     by default
>     dropped 1/2 which has been queued already in the EFI tree
>     use ASCII rather than an opaque constant for "NB10" signature
> 
>  arch/arm64/Kconfig.debug   |  8 ++++
>  arch/arm64/kernel/Makefile |  4 ++
>  arch/arm64/kernel/head.S   | 47 +++++++++++++++++++-
>  3 files changed, 58 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug
> index d1ebd46872fd..f7f38b1aab14 100644
> --- a/arch/arm64/Kconfig.debug
> +++ b/arch/arm64/Kconfig.debug
> @@ -95,6 +95,14 @@ config DEBUG_ALIGN_RODATA
>  
>  	  If in doubt, say N.
>  
> +config DEBUG_EFI
> +	depends on EFI && DEBUG_INFO
> +	bool "UEFI debugging"
> +	help
> +	  Enable this option to include EFI specific debugging features into
> +	  the kernel that are only useful when using a debug build of the
> +	  UEFI firmware
> +

I don't much like embedding the absolute host build path in the kernel
image, but if that's what the tools expect then so be it.

>  source "drivers/hwtracing/coresight/Kconfig"
>  
>  endmenu
> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
> index 7d66bbaafc0c..2600c60337ac 100644
> --- a/arch/arm64/kernel/Makefile
> +++ b/arch/arm64/kernel/Makefile
> @@ -55,3 +55,7 @@ obj-y					+= $(arm64-obj-y) vdso/ probes/
>  obj-m					+= $(arm64-obj-m)
>  head-y					:= head.o
>  extra-y					+= $(head-y) vmlinux.lds
> +
> +ifeq ($(CONFIG_DEBUG_EFI),y)
> +AFLAGS_head.o += -DVMLINUX_PATH="\"$(shell readlink -f $(objtree)/vmlinux)\""
> +endif

Can we use the Make realpath directive instead of calling out to the shell?

Do you want me to merge this via arm64?

Will