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    SubjectRe: [PATCH] Avoid truncating to 'long' in ALIGN() macro
    On Sun, 26 Nov 2006 11:10:23 -0800
    Roland Dreier <rdreier@cisco.com> wrote:

    > Commit 4c8bd7ee ("Do not truncate to 'int' in ALIGN() macro.") was
    > merged to fix the case of code like the following:
    >
    > unsigned long addr;
    > unsigned int alignment;
    > addr = ALIGN(addr, alignment);
    >
    > The original ALIGN macro calculated a mask as ~(alignment - 1), and
    > when alignment is just an int, this creates an int mask. If alignment
    > is also unsigned, then this mask will not be sign extended when
    > promoted to a long, which leads to the code above chopping off the top
    > half of addr when long is 64 bits.
    >
    > However, the changed ALIGN macro, which computes the mask as
    > ~(alignment - 1UL) actually breaks code like the following when long
    > is 32 bits:
    >
    > u64 addr;
    > int alignment;
    > addr = ALIGN(addr, alignment);
    >
    > The reason this breaks is pretty much the same as the original bug
    > that the change was supposed to fix: ~(alignment - 1UL) creates a mask
    > that is an unsigned long, which is not sign extended when promoted to
    > u64 (if long is 32 bits).
    >
    > As suggested by Dave Miller and Al Viro, I fixed this by having the
    > ALIGN macro make sure the alignment is promoted to the same type as
    > the value being aligned before doing the negation.
    >
    > This second construct is actually used in the amso1100 driver, so that
    > driver does not work on 32-bit architectures right now. Unfortunately
    > almost everyone using it runs 64-bit kernels, so this regression was
    > not noticed until now.
    >
    > Signed-off-by: Roland Dreier <rolandd@cisco.com>
    >
    > ---
    > Patch updated as suggested by Dave Miller and Al Viro...
    >
    > can we merge this for 2.6.20?
    >
    > diff --git a/include/linux/kernel.h b/include/linux/kernel.h
    > index 24b6111..80955b3 100644
    > --- a/include/linux/kernel.h
    > +++ b/include/linux/kernel.h
    > @@ -31,7 +31,7 @@ #define ULLONG_MAX (~0ULL)
    > #define STACK_MAGIC 0xdeadbeef
    >
    > #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
    > -#define ALIGN(x,a) (((x)+(a)-1UL)&~((a)-1UL))
    > +#define ALIGN(x,a) ((typeof(x)) (((x) + (a) - 1) & ~((typeof(x)) (a) - 1)))
    > #define FIELD_SIZEOF(t, f) (sizeof(((t*)0)->f))
    > #define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d))
    > #define roundup(x, y) ((((x) + ((y) - 1)) / (y)) * (y))

    I'd be inclined to merge it for 2.6.19. Is everyone OK with it?
    -
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