[Lldb-commits] [lldb] [lldb][test] Strip the MTE tag in TestExpeditedRecentReads (PR #226272)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lldb

Author: Yao Qi (qiyao)

<details>
<summary>Changes</summary>

When the inferior runs with MTE enabled, both heap cases in
`TestExpeditedRecentReads.py` fail at their first stop:

```
AssertionError: [] == [] : the first stop should read the heap buffer from the stub; reads: [0x104da8a00,0x104da8c00)
AssertionError: [] == [] : the first stop should read the heap buffer from the stub; reads: [0x1047acb30,0x1047acb38), [0x1047acb30,0x1047acb38), ...
```

lldb did read the heap buffer. `calloc` returns a pointer with an MTE
tag in its top byte, and lldb strips the tag before it reads memory:

```
(lldb) breakpoint set -p "break here" -f main.c
(lldb) process launch --memory-tagging
...
(lldb) frame variable heap
(Payload *) heap = 0x0b000001005b0b30
(lldb) script v = lldb.frame.FindVariable("heap"); print("GetValueAsUnsigned: 0x%x" % v.GetValueAsUnsigned(0)); print("GetValueAsAddress:  0x%x" % v.GetValueAsAddress())
GetValueAsUnsigned: 0xb000001005b0b30
GetValueAsAddress:  0x1005b0b30
```

Reading `heap->values[0]` then sends `x1005b0a00,200`, which reads the
untagged address. `heap_range` takes the address from
`GetValueAsUnsigned`, which keeps the tag, so `covering` never matches
a read. Use `GetValueAsAddress`, which returns the address with the
non-addressable bits cleared.

Assisted-by: claude


---
Full diff: https://github.com/llvm/llvm-project/pull/226272.diff


1 Files Affected:

- (modified) lldb/test/API/macosx/expedited-recent-reads/TestExpeditedRecentReads.py (+1-1) 


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</details>


https://github.com/llvm/llvm-project/pull/226272