Messages in this thread Patch in this message | | | From | Paul Heidekrüger <> | Subject | [PATCH] tools/memory-model: Weaken ctrl dependency definition in explanation.txt | Date | Tue, 30 Aug 2022 20:44:46 +0000 |
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The current informal control dependency definition in explanation.txt is too broad and, as dicsussed, needs to be updated.
Consider the following example:
> if(READ_ONCE(x)) > return 42; > > WRITE_ONCE(y, 42); > > return 21;
The read event determines whether the write event will be executed "at all" - as per the current definition - but the formal LKMM does not recognize this as a control dependency.
Introduce a new defintion which includes the requirement for the second memory access event to syntactically lie within the arm of a non-loop conditional.
Link: https://lore.kernel.org/all/20220615114330.2573952-1-paul.heidekrueger@in.tum.de/ Cc: Marco Elver <elver@google.com> Cc: Charalampos Mainas <charalampos.mainas@gmail.com> Cc: Pramod Bhatotia <pramod.bhatotia@in.tum.de> Cc: Soham Chakraborty <s.s.chakraborty@tudelft.nl> Cc: Martin Fink <martin.fink@in.tum.de> Signed-off-by: Paul Heidekrüger <paul.heidekrueger@in.tum.de> Co-developed-by: Alan Stern <stern@rowland.harvard.edu> ---
@Alan:
Since I got it wrong the last time, I'm adding you as a co-developer after my SOB. I'm sorry if this creates extra work on your side due to you having to resubmit the patch now with your SOB if I understand correctly, but since it's based on your wording from the other thread, I definitely wanted to give you credit.
tools/memory-model/Documentation/explanation.txt | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/tools/memory-model/Documentation/explanation.txt b/tools/memory-model/Documentation/explanation.txt index ee819a402b69..0bca50cac5f4 100644 --- a/tools/memory-model/Documentation/explanation.txt +++ b/tools/memory-model/Documentation/explanation.txt @@ -464,9 +464,10 @@ to address dependencies, since the address of a location accessed through a pointer will depend on the value read earlier from that pointer.
-Finally, a read event and another memory access event are linked by a -control dependency if the value obtained by the read affects whether -the second event is executed at all. Simple example: +Finally, a read event X and another memory access event Y are linked by +a control dependency if Y syntactically lies within an arm of an if, +else or switch statement and the condition guarding Y is either data or +address-dependent on X. Simple example:
int x, y;
-- 2.35.1
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