Dear Mike, In message <200901021742.05363.vap...@gentoo.org> you wrote: > > > > +__u8 get_vfatname_block[MAX_CLUSTSIZE] __attribute__ > > > ((aligned(sizeof(__u16)))); > > ... > > > +__u8 get_dentfromdir_block[MAX_CLUSTSIZE] __attribute__ > > > ((aligned(sizeof(__u32)))); > > ... > > > +__u8 do_fat_read_block[MAX_CLUSTSIZE] __attribute__ > > > ((aligned(sizeof(__u32)))); > > > > What makes you sure that a 16 resp. 32 bit alignment is sufficient, > > and that gcc does not decide to align such structures even stricter? > > read the structures in question. the largest member is 16bit/32bit. i > really > dont know what other alignment gcc could randomly generate.
It is not (only) the size of the "largest" member in a struct which determins global alignment, but also the size of the struct itself. See for example http://gcc.gnu.org/onlinedocs/gcc-4.3.2/gcc/Type-Attributes.html Read especially this part: In the example above, if the size of each short is 2 bytes, then the size of the entire struct S type is 6 bytes. The smallest power of two which is greater than or equal to that is 8, so the compiler sets the alignment for the entire struct S type to 8 bytes. > > Wouldn't it make more sense to use "__alignof__ ()" here to be on the > > safe side? > > i found no such alignment attribute in the gcc docs which is why i suggested > Bryan use aligned(sizeof(...)). > http://gcc.gnu.org/onlinedocs/gcc-4.3.2/gcc/Function-Attributes.html > http://gcc.gnu.org/onlinedocs/gcc-4.3.2/gcc/Variable-Attributes.html > http://gcc.gnu.org/onlinedocs/gcc-4.3.2/gcc/Type-Attributes.html Maybe you should have searched for the (IMHO pretty obvious) term "Alignment" as well, i.e. look at http://gcc.gnu.org/onlinedocs/gcc-4.3.2/gcc/Alignment.html#Alignment Quote: The keyword __alignof__ allows you to inquire about how an object is aligned, or the minimum alignment usually required by a type. Its syntax is just like sizeof. Best regards, Wolfgang Denk -- DENX Software Engineering GmbH, MD: Wolfgang Denk & Detlev Zundel HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: w...@denx.de The more sins you confess, the more books you will sell. _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
