Re: [PATCH 1/2 v2] FLAT: split the stack & data alignments

[David McCullough <david_mccullough@mcafee.com>]

Jivin Mike Frysinger lays it down ...
> The stack and data have different alignment requirements, so don't force
> them to wear the same shoe.  Increase the data alignment to match that
> which the elf2flt linker script has always been using: 0x20 bytes.  Not
> only does this bring the kernel loader in line with the toolchain, but
> it also fixes a swath of gcc tests which try to force larger alignment
> values but randomly fail when the FLAT loader fails to deliver.
> 
> Signed-off-by: Mike Frysinger <vapier@gentoo.org>

Acked-by: David McCullough <david_mccullough@mcafee.com>

Cheers,
Davidm

> ---
> v2
> 	- split changes & document better
> 
>  fs/binfmt_flat.c |   23 +++++++++++++++--------
>  1 files changed, 15 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c
> index 49566c1..b865622 100644
> --- a/fs/binfmt_flat.c
> +++ b/fs/binfmt_flat.c
> @@ -56,15 +56,22 @@
>  #endif
>  
>  /*
> - * User data (stack, data section and bss) needs to be aligned
> - * for the same reasons as SLAB memory is, and to the same amount.
> - * Avoid duplicating architecture specific code by using the same
> - * macro as with SLAB allocation:
> + * User data (data section and bss) needs to be aligned.
> + * We pick 0x20 here because it is the max value elf2flt has always
> + * used in producing FLAT files, and because it seems to be large
> + * enough to make all the gcc alignment related tests happy.
> + */
> +#define FLAT_DATA_ALIGN	(0x20)
> +
> +/*
> + * User data (stack) also needs to be aligned.
> + * Here we can be a bit looser than the data sections since this
> + * needs to only meet arch ABI requirements.
>   */
>  #ifdef ARCH_SLAB_MINALIGN
> -#define FLAT_DATA_ALIGN	(ARCH_SLAB_MINALIGN)
> +#define FLAT_STACK_ALIGN	(ARCH_SLAB_MINALIGN)
>  #else
> -#define FLAT_DATA_ALIGN	(sizeof(void *))
> +#define FLAT_STACK_ALIGN	(sizeof(void *))
>  #endif
>  
>  #define RELOC_FAILED 0xff00ff01		/* Relocation incorrect somewhere */
> @@ -129,7 +136,7 @@ static unsigned long create_flat_tables(
>  
>  	sp = (unsigned long *)p;
>  	sp -= (envc + argc + 2) + 1 + (flat_argvp_envp_on_stack() ? 2 : 0);
> -	sp = (unsigned long *) ((unsigned long)sp & -FLAT_DATA_ALIGN);
> +	sp = (unsigned long *) ((unsigned long)sp & -FLAT_STACK_ALIGN);
>  	argv = sp + 1 + (flat_argvp_envp_on_stack() ? 2 : 0);
>  	envp = argv + (argc + 1);
>  
> @@ -876,7 +883,7 @@ static int load_flat_binary(struct linux_binprm * bprm, struct pt_regs * regs)
>  	stack_len = TOP_OF_ARGS - bprm->p;             /* the strings */
>  	stack_len += (bprm->argc + 1) * sizeof(char *); /* the argv array */
>  	stack_len += (bprm->envc + 1) * sizeof(char *); /* the envp array */
> -	stack_len += FLAT_DATA_ALIGN - 1;  /* reserve for upcoming alignment */
> +	stack_len += FLAT_STACK_ALIGN - 1;  /* reserve for upcoming alignment */
>  	
>  	res = load_flat_file(bprm, &libinfo, 0, &stack_len);
>  	if (IS_ERR_VALUE(res))
> -- 
> 1.7.1
> 
> 
> 

-- 
David McCullough,      david_mccullough@mcafee.com,  Ph:+61 734352815
McAfee - SnapGear      http://www.mcafee.com         http://www.uCdot.org