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[lldb] Show memory tags in memory read output
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Authored by DavidSpickett on Jul 30 2021, 2:25 AM.



This extends DumpDataExtractor to also print memory
tags if called with an execution context on a target
that has memory tagging.

(lldb) memory read mte_buf mte_buf+32 -f "x" -s8
0x900fffff7ff8000: 0x0000000000000000 0x0000000000000000 (tag: 0x0)
0x900fffff7ff8010: 0x0000000000000000 0x0000000000000000 (tag: 0x1)

Tags are printed on the end of each line, if that
line has any tags associated with it. Meaning that
untagged memory output is unchanged.

Tags are printed based on the granule(s) of memory that
a line covers. So you may have lines with 1 tag, with many
tags, no tags or partially tagged lines.

There are no special alignment requirements, simply
use "memory read" as usual. All alignment is handled
in DumpDataExtractor.

In the case of partially tagged lines, untagged granules
will show "<no tag>" so that the ordering is obvious.
For example, a line that covers 2 granules where the first
is not tagged:

(lldb) memory read mte_buf-16 mte_buf+16 -l32 -f"x"
0x900fffff7ff7ff0: 0x00000000 <...> (tags: <no tag> 0x0)

The tags are read from a new class MemoryTagMap which
is a sparse map of tag read results.

Using the new tag manager method MakeTaggedRanges you
can get all the sub-ranges of a larger range, that
have memory tagging.

Then loop over these calling ReadMemoryTags, insert them
into the map and request as needed when printing memory dumps.

The tag map is populated once in DumpDataExtractor and re-used
for each subsequently printed line (or recursive call of
DumpDataExtractor, which some formats do).

Diff Detail

Event Timeline

DavidSpickett created this revision.Jul 30 2021, 2:25 AM
DavidSpickett requested review of this revision.Jul 30 2021, 2:25 AM
Herald added a project: Restricted Project. · View Herald TranscriptJul 30 2021, 2:25 AM
DavidSpickett added a subscriber: pcc.

DumpDataExtractor has formatting unittests. Due to memory tags being read from the execution context there are no new unittests. (the existing ones pass)

Also since this code isn't exactly simple and could have issues, and tags will be right most of the time I think an opt in to this feature makes sense. I haven't added that here yet but will do if you agree. Not yet sure if it would be an option to "memory read", or a debugger setting.

@pcc We talked about tag formatting in an earlier patch. Your feedback on the format I've gone with would be great.

Also Omair we talked about 13 backports to get MTE support to a good place. This is one that I think would be ok to not do so, given that tag reading can be done manually as needed and it has some complexity to be considered.