[cfe-dev] [llvm-dev] [3.8 Release] Please write release notes!

Joerg Sonnenberger via cfe-dev cfe-dev at lists.llvm.org
Thu Mar 3 06:05:22 PST 2016


On Wed, Mar 02, 2016 at 11:34:27PM -0800, John McCall via llvm-dev wrote:
> When that’s not practical, you can instead reduce the alignment requirements
> of the pointer.  If the pointer is to a struct that represents that layout of a
> serialized structure, consider making that struct packed; this will remove any
> implicit internal padding that the compiler might add to the struct and
> reduce its alignment requirement to 1.
> 
>   struct file_header {
>     uint16_t magic_number;
>     uint16_t format_version;
>     uint16_t num_entries;
>   } __attribute__((packed));

If we want to include this example, it is likely a good idea to point
out that packed and aligned can be combined, i.e. if you know that the
file_header copies are going to be at an aligned location, adding the
attribute results in significantly better code on platforms like ARM
with strict alignment.

Joerg


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