cvs commit: src/sys/geom geom_gpt.c
marcel at FreeBSD.org
Sun Jun 4 20:28:06 UTC 2006
marcel 2006-06-04 20:26:13 UTC
FreeBSD src repository
Fix unaligned memory accesses on Alpha and possible other platforms.
By using a pointer to struct dos_partition, we implicitly tell the
compiler that the pointer is 4-bytes aligned, even though we know
that's not the case. The fact that we only dereference the pointer
to access a byte-wide field (field dp_ptyp) is not a guarantee that
the compiler will in fact use a byte-wide load. On some platforms
it's more efficient to use long word or quad word loads and use
bit-shifting and bit-masking to get the intended byte. On those
platforms an misaligned load will be the result.
The fix is to use byte-wide pointer arithmetic based on sizeof() and
offsetof() to avoid invalid casts which avoids that the compiler
makes invalid assumptions.
Backtrace provided by: wilko@
MFC after: 1 week
Revision Changes Path
1.38 +4 -3 src/sys/geom/geom_gpt.c
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