swh:1:snp:13806c77fd4b7f42b1e985e730bd615fd52cfac1
Revision 1a499150e4ec1299232e24389f648d059ce5617a authored by Luck, Tony on 14 January 2008, 17:59:24 UTC, committed by Tony Luck on 15 January 2008, 22:26:55 UTC
The compiler team did the hard work for this distilling a problem in
large fortran application which showed up when applied to a 290MB input
data set down to this instruction:

	ldfd f34=[r17],-8

Which they noticed incremented r17 by 0x10 rather than decrementing it
by 8 when the value in r17 caused an unaligned data fault.  I tracked
it down to some bad instruction decoding in unaligned.c. The code
assumes that the 'x' bit can determine whether the instruction is
an "ldf" or "ldfp" ... which it is for opcode=6 (see table 4-29 on
page 3:302 of the SDM).  But for opcode=7 the 'x' bit is irrelevent,
all variants are "ldf" instructions (see table 4-36 on page 3:306).

Note also that interpreting the instruction as "ldfp" means that the
"paired" floating point register (f35 in the example here) will also
be corrupted.

Signed-off-by: Tony Luck <tony.luck@intel.com>
1 parent 0938e75
History
Tip revision: 52e44129fba5cfc4e351fdb5e45849afc74d9a53 authored by Linus Torvalds on 10 April 2021, 19:51:12 UTC
Merge branch 'for-5.12-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/dennis/percpu
Tip revision: 52e4412
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