Hi, Sergey,

Hi, folks!
Some more thoughts below.

On 15.05.24, Sergey Kaplun wrote:

<snipped>

+  string(JOIN "," UBSAN_IGNORE_OPTIONS
+    # Misaligned pseudo-pointers are used to determine internal
+    # variable names inside the `for` cycle.
+    alignment
+    # Not interested in float cast overflow errors.
+    float-cast-overflow
+    # NULL checking is disabled because this is not a UB and
+    # raises lots of false-positive fails.
+    null

Maybe it is worth to add also "nonnull-attribute" to the ignore options:

```
LSAN_OPTIONS="abort_on_error=1" src/luajit -e 'error("bad usage", 3)'
/home/burii/builds_workspace/luajit/gh-8473-ubsan/src/lj_buf.h:75:25: runtime error: null pointer passed as argument 1, which is declared to never be null
/usr/include/string.h:44:28: note: nonnull attribute specified here
```

Here, `memcpy()` gets the NULL pointer as the first argument and the
`len` == 0. So there are no problems here. Also, the nullability
violation is not a UB, as mentioned in the documentation.

Thoughts?

I agree with arguments provided by Maxim - it's UB, the standard states it clearly,

and it should be fixed. I propose to do the following:

- suppress the check (add it to UBSAN_IGNORE_OPTIONS) with appropriate comment

(something like "we know it is bad, but it is unfixed in upstream, we will wait a fix").

Probably we should suppress it per file like you did with other checks.

- send a fix to upstream or submit an issue to the upstream (I'll not insist, but it would be desirable)

+    # Not interested in checking arithmetic with NULL.
+    pointer-overflow
+    # Shifts of negative numbers are widely used in parsing ULEB,
+    # cdata arithmetic, vmevent hash calculation, etc.
+    shift-base
+  )