Messages in this thread | ![/](/images/icornerl.gif) | | From | David Laight <> | Subject | RE: [PATCH v2] x86/asm: fix assembly constraints in bitops | Date | Tue, 2 Apr 2019 11:45:20 +0000 |
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From: Alexander Potapenko > Sent: 02 April 2019 12:28 > > 1. Use memory clobber in bitops that touch arbitrary memory > > Certain bit operations that read/write bits take a base pointer and an > arbitrarily large offset to address the bit relative to that base.
Although x86_64 can use a signed 64bit bit number, looking at arm and arm64 they use 'int nr' throughout as do the generic functions. Maybe x86 ought to be consistent here. I doubt negative bit numbers are expected to work?
Did you try telling gcc that a big buffer (250MB is the limit for 32bit) from the pointer might be changed? That ought to be softer than a full 'memory' clobber as it should only affect memory that could be accessed through the pointer.
.... > -#define BITOP_ADDR(x) "+m" (*(volatile long *) (x)) > +#define RLONG_ADDR(x) "m" (*(volatile long *) (x)) > +#define WBYTE_ADDR(x) "+m" (*(volatile char *) (x)) > > -#define ADDR BITOP_ADDR(addr) > +#define ADDR RLONG_ADDR(addr)
Is it worth just killing ADDR ? (as a different patch)
David
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