Re: [PATCH] alpha: spinlock: don't perform memory access in locked critical section
From: Al Viro <viro@ZenIV.linux.org.uk>
Date: 2013-05-06 20:53:34
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From: Al Viro <viro@ZenIV.linux.org.uk>
Date: 2013-05-06 20:53:34
Also in:
lkml
On Mon, May 06, 2013 at 01:19:51PM -0700, Matt Turner wrote:
I'm not sure of the interpretation that LDA counts as a memory access. The manual says it's Ra <- Rbv + SEXT(disp). It's not touching memory that I can see.
More to the point, the same manual gives explicit list of instructions that shouldn't occur between LDx_L and STx_C, and LDA does not belong to any of those. I suspect that Will has misparsed the notations in there - LDx is present in the list, but it's _not_ "all instructions with mnemonics starting with LD", just the 4 "load integer from memory" ones. FWIW, instructions with that encoding (x01xxx<a:5><b:5><offs:16>) are grouped so: LDAx - LDA, LDAH; load address LDx - LDL, LDQ, LDBU, LDWU; load memory data into integer register LDQ_U; load unaligned LDx_L - LDL_L, LDQ_L; load locked STx_C - STL_C, STQ_C; store conditional STx - STL, STQ, STB, STW; store STQ_U; store unaligned They all have the same encoding, naturally enough (operation/register/address representation), but that's it... See section 4.2 in reference manual for details; relevant note follows discussion of LDx_L and it spells the list out. LDx is present, LDAx isn't (and neither is LDA by itself).