Greg, On 25.10.2013 08:42, Greg Price wrote: > It's not true that the return value is suitably aligned for "any > variable"; for example, it's unsuitable for a variable like > float *x __attribute__ ((__vector_size__ (32))); > which requires 32-byte alignment. Types like this are defined in > <avxintrin.h>, and with 16-byte alignment in <emmintrin.h> and > <xmmintrin.h>, so the application programmer need not even know > that a vector_size attribute has been applied. > > On an x86 architecture, a program that loads from or stores to a > pointer with this type derived from malloc can crash because GCC > generates an aligned load/store, like MOVDQA. > > The C99 standard (TC3, as of N1256) does say the return value is > suitably aligned for "any type of object". The C11 standard (as > of N1570) revises this to any type with "fundamental alignment", > which means an alignment "supported by the implementation in all > contexts", which I suppose tautologically includes aligning > malloc/realloc return values. > > The actual behavior of current glibc malloc is to align to the > greater of 2 * sizeof(size_t) and __alignof__ (long double), > which may be one bit greater than this commit promises. Thanks for the patch and the excellent commit message. I've applied. Cheers, Michael > Signed-off-by: Greg Price <price@xxxxxxx> > --- > man3/malloc.3 | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/man3/malloc.3 b/man3/malloc.3 > index 372b503..84d9852 100644 > --- a/man3/malloc.3 > +++ b/man3/malloc.3 > @@ -131,8 +131,8 @@ The > .BR malloc () > and > .BR calloc () > -functions return a pointer to the allocated memory > -that is suitably aligned for any kind of variable. > +functions return a pointer to the allocated memory, > +which is suitably aligned for any built-in type. > On error, these functions return NULL. > NULL may also be returned by a successful call to > .BR malloc () > @@ -154,7 +154,7 @@ function returns no value. > The > .BR realloc () > function returns a pointer to the newly allocated memory, which is suitably > -aligned for any kind of variable and may be different from > +aligned for any built-in type and may be different from > .IR ptr , > or NULL if the request fails. > If > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ My next Linux/UNIX system programming course: -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
