Hi Michael,
Michael Buesch wrote:
On Tuesday 02 June 2009 00:00:12 matthieu castet wrote:
matthieu castet wrote:
Hi,
b43_generate_plcp_hdr generate unaligned access on mips with gcc [1]
from openwrt.
A small testcase [2] show that &plcp->data is access as a 32 bit aligned
variable (see the "lw $2,0($4)" and "sw $2,0($4)").
I don't know enough mips to know if it is a gcc bug (ignoring the packed
attribute) or something missing in b43 code.
For example using "plcp->data" instead "*data" produce the correct code.
Uhm, I'm not sure. This code has been in the driver as-is forever and I don't
see any unaligned access issues on mips (I checked a month or so ago).
Where does this pointer come from ? May be other code change change this
pointer alignement?
Which toolchain did you use ?
Could you try to build the testcase I posted and see which code it
generate ?
The plcp data structure is also __attribute__((packed)), so there can't be any
unaligned accesses, as gcc is required to _expect_ unaligned accesses on structures
with packed attribute. So it is required to do byte accesses on architectures where
alignment matters.
So I don't think there's an issue in the code.
But the code doesn't use the structure to access the data.
It use by an extra pointer "data", and I believe gcc loose the packed
info (use byte accesses) when we do the "u32 *data = &plcp->data".
Matthieu
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