Messages in this thread | | | Date | Fri, 30 Nov 2007 08:58:28 +0100 | From | DM <> | Subject | Re: [RFC v2] Documentation about unaligned memory access |
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On Nov 29, 2007 5:15 PM, Daniel Drake <dsd@gentoo.org> wrote: [...] > To avoid the unaligned memory access, you would rewrite it as follows: > > void myfunc(u8 *data, u32 value) > { > [...] > value = cpu_to_le32(value); > put_unaligned(value, data); > [...] > } > > The get_unaligned() macro works similarly. Assuming 'data' is a pointer to > memory and you wish to avoid unaligned access, its usage is as follows: > > u32 value = get_unaligned(data); > > These macros work work for memory accesses of any length (not just 32 bits as > in the examples above). Be aware that when compared to standard access of > aligned memory, using these macros to access unaligned memory can be costy in > terms of performance. >
The get_unaligned call above will not do what you intended given the, at least as I read it, implied context of myfunc. Since data is a u8* it will only get one byte of data. To avoid misunderstandings the code should probably read:
u32 value = get_unaligned((u32 *)data);
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