[lwip-devel] [bug #26273] etharp.c : fix alignment issue in etharp_raw

[Guillaume du PONTAVICE]

Follow-up Comment #4, bug #26273 (project lwip):

ok here is the assembly dump


ldl n = (Load local) Load the value from n words above WPTR.
ldnlp n  = (Load non-local pointer) Load the value AREG + 4n.
dup = duplicate top of stack
stnl n = Store non-local Store a value to n words above AREG.
rev = reverse AREG & BREG value
adc n = add constant to AREG


        -- Line 1081 (lwip/src/netif/etharp.c) 
..2719: -- Line 1081 (lwip/src/netif/etharp.c) 
        ldl     5       -- hdr
        ldnlp   7
        dup
        ldl     12      -- ipsrc_addr
        ldnl    0
        rev
        stnl    0
        -- Line 1082 (lwip/src/netif/etharp.c) 
..2720: -- Line 1082 (lwip/src/netif/etharp.c) 
        ldl     5       -- hdr
        adc     38
        dup
        ldl     14      -- ipdst_addr
        ldnl    0
        rev
        stnl    0


as we can see, ipsrc_addr field is word aligned (instruction ldnlp 7 : offset
= 7  words = 28 bytes) a load word / store word operation is used.

ipdst_addr field is not word aligned (instruction adc 38 : offset = 38
bytes), but the compiler still uses a load word / store word operation.

so it is a compiler bug.
I will report a bug to ST but unfortunately I doubt I can get a compiler fix
in a short term ....

would it be possible to use the SMEMCPY alternative ?


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