[lwip-devel] [bug #50883] struct eth_addr alignment error

[Daniel Elstner]

URL:
  <http://savannah.nongnu.org/bugs/?50883>

                 Summary: struct eth_addr alignment error
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: danielk
            Submitted on: Wed 26 Apr 2017 04:13:16 PM CEST
                Category: ARP
                Severity: 3 - Normal
              Item Group: Crash Error
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None
            lwIP version: git head

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Details:

I tracked down a crash in my project to an alignment fault in etharp_raw(). In
the crashing case one of the arguments points to the global constant ethzero,
which is a struct eth_addr. This struct has only 8-bit members so the compiler
is free to place it at any byte address. Since I define ETHADDR16_COPY() to
use 16-bit reads/writes, an alignment exception is triggered.

The minimum alignment could be changed by making the type a union including
some u16_t members, or a compiler attribute could be used. However, that would
still not help if struct packing is enabled (it would work for me only because
I happen to disable it).

I think it's wrong for the ARP code to use the same packed type from the proto
header for its own local/global variables.




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