[scudo] document allocation_ring_buffer_size (#71812)

Author: fmayer

llvm/docs/ScudoHardenedAllocator.rst

@@ -250,6 +250,22 @@ The following "string" options are available:
 |                                 |                |                | can be attempted (a negative value disables     |
 |                                 |                |                | reclaiming).                                    |
 +---------------------------------+----------------+----------------+-------------------------------------------------+
+| allocation_ring_buffer_size     | 32768          | n/a            | If stack trace collection is requested, how     |
+|                                 |                |                | many previous allocations to keep in the        |
+|                                 |                |                | allocation ring buffer.                         |
+|                                 |                |                |                                                 |
+|                                 |                |                | This buffer is used to provide allocation and   |
+|                                 |                |                | deallocation stack traces for MTE fault         |
+|                                 |                |                | reports. The larger the buffer, the more        |
+|                                 |                |                | unrelated allocations can happen between        |
+|                                 |                |                | (de)allocation and the fault.                   |
+|                                 |                |                | If your sync-mode MTE faults do not have        |
+|                                 |                |                | (de)allocation stack traces, try increasing the |
+|                                 |                |                | buffer size.                                    |
+|                                 |                |                |                                                 |
+|                                 |                |                | Stack trace collection can be requested using   |
+|                                 |                |                | scudo_malloc_set_track_allocation_stacks        |
++---------------------------------+----------------+----------------+-------------------------------------------------+
 
 Additional flags can be specified, for example if Scudo if compiled with
 `GWP-ASan <https://llvm.org/docs/GwpAsan.html>`_ support.