Maybe Valgrind has an API now to attach a backtrace to a custom allocation out of an arena. I haven't touched that in years. I did the initial Valgrind integration in 2009 and just maintained it with changes to the gc.

I see this in the current manual:

VALGRIND_MALLOCLIKE_BLOCK:

If your program manages its own memory instead of using the standard malloc / new / new[], tools that track information about heap blocks will not do nearly as good a job. For example, Memcheck won't detect nearly as many errors, and the error messages won't be as informative. To improve this situation, use this macro just after your custom allocator allocates some new memory. See the comments in valgrind.h for information on how to use it.

I can't remember whether I saw this before; i.e. is this something existing that had not been useful, or is it something new. I will look into it.

It does look like it should be attacking the same problem: that the errors aren't detected well or nearly as informative in blocks carved out of larger block by custom allocators.

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