Date: Sun, 4 Jun 2006 20:26:13 +0000 (UTC) From: Marcel Moolenaar <marcel@FreeBSD.org> To: src-committers@FreeBSD.org, cvs-src@FreeBSD.org, cvs-all@FreeBSD.org Subject: cvs commit: src/sys/geom geom_gpt.c Message-ID: <200606042026.k54KQDRp051694@repoman.freebsd.org>
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marcel 2006-06-04 20:26:13 UTC
FreeBSD src repository
Modified files:
sys/geom geom_gpt.c
Log:
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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