Re: [lwip-devel] [bug #39683] Assertion "seg->tcphdr not aligned" failed with MEM_ALIGNMENT = 8

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Sylvain Rochet wrote:
> Follow-up Comment #5, bug #39683 (project lwip):
>
> It also breaks things for MEM_ALIGNMENT==1, MEM_ALIGNMENT is historically set
> to 1 in unix port minimal example by default.
>
> Most x86_64 CPUs are able to do unaligned access without any cost penalty so
> that's actually a fine default for unix ports.

Without any cost penalty? How's that possible when the data to load 
spreads accros 2 system bus addresses?

It's true that these CPUs support loading unaligned data, but AFAIK 
there can still be a performance penalty due to executing 2 loads that 
are then merged and shifted to get the requested data, or has this changed?


Simon