nic@nicwatson.org wrote:

That's news to me. Then I googled it. You're right.

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From https://wiki.sei.cmu.edu/confluence/display/c/EXP36-C.+Do+not+cast+pointers+...

The C Standard, 6.3.2.3, paragraph 7 [ISO/IEC 9899:2011], states

A pointer to an object or incomplete type may be converted to a pointer to a different object or incomplete type. If the resulting pointer is not correctly aligned for the referenced type, the behavior is undefined.

Nic

On Tue, Mar 20, 2018 at 9:41 AM, Hallvard Breien Furuseth h.b.furuseth@usit.uio.no wrote:

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Looks like another type aliasing problem to me. The data is accessed through an MDB_page* variable. This tells the compiler that the data is word-aligned, like struct MDB_page. Fix: Use a void/char pointer, don't lie to the compiler.

Good catch.

We once discussed padding odd-length keys to make sure the data was still word-aligned. Maybe should do that in LMDB 1.0. This particular crash is now fixed in mdb.master. I've left other derefs of *fp alone for the moment but may need to revisit that later; older ARM and SPARC would probably choke on them.