Dear Reinhard Meyer, In message <[email protected]> you wrote: > > In a non-packed struct an int will never be unaligned > (unless you use an unaligned pointer to the whole struct)
Which may happen for example when overlaying such a struct on top of some I/O buffer. > In a packed struct an int might be unaligned, so it > _might_ make sense for the compiler to handle that > differently on ARM. Assume you overlay (bad idea anyway) In a packed struct, where the struct itself is located with sufficient alignment, and where all previous elements in the struct are sufficiently aligned (like in the example I gave), it is NOT possible that such unaligment happens. > a packed structure over some communication data stream > thats is byte oriented. On most architectures that would > work (besides obvious endianess issues) but on ARM it would > (without raising an exception) malfunction. Keep in mind that the compiler knows the start address of the struct, and the alignment of the elements. It could easily determine that no unaligned accesses can result. With the same logic you would have to enforce byte accesses for the not-packed structs as well, as theese might be accessed through a not sufficiently aligned pointer. > So the "status_reg" pointer is in a completely unrelated (to the packed > struct) > "u32 *" and still the access is done like it was packed. If the > compiler silently drags that attribute along into the "u32 *" > THAT is really sick! We do agree on this statement. GCC on ARM is a strange beast. 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: [email protected] "The whole problem with the world is that fools and fanatics are always so certain of themselves, but wiser people so full of doubts." - Bertrand Russell _______________________________________________ U-Boot mailing list [email protected] http://lists.denx.de/mailman/listinfo/u-boot
