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    SubjectRe: [PATCH 1/2 v2] FLAT: split the stack & data alignments
    Mike Frysinger wrote:
    > 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: Greg Ungerer <gerg@uclinux.org>


    > ---
    > 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))


    --
    ------------------------------------------------------------------------
    Greg Ungerer -- Principal Engineer EMAIL: gerg@snapgear.com
    SnapGear Group, McAfee PHONE: +61 7 3435 2888
    8 Gardner Close FAX: +61 7 3217 5323
    Milton, QLD, 4064, Australia WEB: http://www.SnapGear.com


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