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runtime: audit mapfast routines for indirectvalue support #21547

josharian opened this issue Aug 21, 2017 · 3 comments


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commented Aug 21, 2017

On reflection, the most recent CLs I mailed suggest that mapdelete_fast* might not be handing indirect value maps correctly. I'm out of computer time for today and maybe tomorrow as well. Filing this as a reminder, and because these were newly introduced in 1.9, and if they're not well-handled, it could cause memory corruption. Should double check all routines, really.


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commented Aug 21, 2017


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commented Aug 21, 2017

@josharian indirect values always use the slow map:

See cmd/compile/internal/gc/walk.go

2838 func mapfast(t *types.Type) int {
2839     // Check ../../runtime/hashmap.go:maxValueSize before changing.
2840     if t.Val().Width > 128 {
2841         return mapslow
2842     }
2843     switch algtype(t.Key()) {
2844     case AMEM32:
2845         return mapfast32
2846     case AMEM64:
2847         return mapfast64
2848     case ASTRING:
2849         return mapfaststr
2850     }
2851     return mapslow
2852 }

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commented Aug 22, 2017

Yes, this should be fine. Fast versions do not need to handle indirect values.
It would be nice to have a test, though.

@josharian josharian added the Testing label Aug 28, 2017

@ianlancetaylor ianlancetaylor added this to the Unplanned milestone Mar 30, 2018

@martisch martisch self-assigned this Jan 18, 2019

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