linux-kernel - Re: [PATCH] arm64: extable: sort the exception table at build time

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Date:	Fri, 17 May 2013 11:33:53 -0700
From:	David Daney <ddaney.cavm@...il.com>
To:	Will Deacon <will.deacon@....com>
CC:	catalin.marinas@....com, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, david.daney@...ium.com
Subject: Re: [PATCH] arm64: extable: sort the exception table at build time

On 05/17/2013 09:43 AM, Will Deacon wrote:
> As is done for other architectures, sort the exception table at
> build-time rather than during boot.
>
> Since sortextable appears to be a standalone C program relying on the
> host elf.h to provide EM_AARCH64, I've had to add a conditional check in
> order to allow cross-compilation on machines that aren't running a
> bleeding-edge libc-dev.
>
> Signed-off-by: Will Deacon <will.deacon@....com>
> ---
>   arch/arm64/Kconfig              |  1 +
>   arch/arm64/kernel/vmlinux.lds.S | 15 +++++++--------
>   scripts/sortextable.c           |  5 +++++
>   3 files changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 48347dc..fb8fd90 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -7,6 +7,7 @@ config ARM64
>   	select ARM_AMBA
>   	select ARM_ARCH_TIMER
>   	select ARM_GIC
> +	select BUILDTIME_EXTABLE_SORT
>   	select CLONE_BACKWARDS
>   	select COMMON_CLK
>   	select GENERIC_CLOCKEVENTS
> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
> index 3fae2be..3d527726 100644
> --- a/arch/arm64/kernel/vmlinux.lds.S
> +++ b/arch/arm64/kernel/vmlinux.lds.S
> @@ -57,6 +57,13 @@ SECTIONS
>
>   	RO_DATA(PAGE_SIZE)
>
> +	. = ALIGN(8);
> +	__ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) {
> +		__start___ex_table = .;
> +		*(__ex_table)
> +		__stop___ex_table = .;
> +	}
> +
>   	_etext = .;			/* End of text and rodata section */


You have moved this to rodata.

o Will the runtime sort still work like this?

o Do we care?  Maybe not.

David Daney


>
>   	. = ALIGN(PAGE_SIZE);
> @@ -99,14 +106,6 @@ SECTIONS
>   		READ_MOSTLY_DATA(64)
>
>   		/*
> -		 * The exception fixup table (might need resorting at runtime)
> -		 */
> -		. = ALIGN(32);
> -		__start___ex_table = .;
> -		*(__ex_table)
> -		__stop___ex_table = .;
> -
> -		/*
>   		 * and the usual data section
>   		 */
>   		DATA_DATA
> diff --git a/scripts/sortextable.c b/scripts/sortextable.c
> index 1f10e89..f9ce116 100644
> --- a/scripts/sortextable.c
> +++ b/scripts/sortextable.c
> @@ -31,6 +31,10 @@
>   #include <tools/be_byteshift.h>
>   #include <tools/le_byteshift.h>
>
> +#ifndef EM_AARCH64
> +#define EM_AARCH64	183
> +#endif
> +
>   static int fd_map;	/* File descriptor for file being modified. */
>   static int mmap_failed; /* Boolean flag. */
>   static void *ehdr_curr; /* current ElfXX_Ehdr *  for resource cleanup */
> @@ -249,6 +253,7 @@ do_file(char const *const fname)
>   		custom_sort = sort_relative_table;
>   		break;
>   	case EM_ARM:
> +	case EM_AARCH64:
>   	case EM_MIPS:
>   		break;
>   	}  /* end switch */
>

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