MPS issue job003882

Titlesncss test failure
Assigned userGareth Rees
Descriptionsncss fails on xci6ll with seed 1817331918 with this assertion:

    poolsnc.c:317: MPS ASSERTION FAILED: free != NULL
AnalysisThe assertion is triggered when an allocation frame is popped from an buffer, but SNC cannot find the segment to pop to in the chain of segments attached to the buffer.

That's because SNC records the address to pop to using this logic in SNCFramePush [1]:

    /* Use the scan limit as the lightweight frame pointer */
    *frameReturn = (AllocFrame)BufferScanLimit(buf);

(and similarly in mps_alloc_frame_push [2]) and then when the frame is popped SNC finds the segment to pop to by calling SegOfAddr on this address. But this fails when BufferScanLimit(buf) is the limit of the segment: then SegOfAddr will, if it succeeds, get the next segment in memory.
How foundautomated_test
Test proceduresncss
Created byGareth Rees
Created on2014-10-12 11:18:37
Last modified byGareth Rees
Last modified on2014-10-20 17:06:34
History2014-10-12 GDR Created.


Change Effect Date User Description
187220 closed 2014-10-12 11:58:13 Gareth Rees Don't set a frame pointer at the limit of a segment, as this is ambiguous: is it at the limit of the segment, or at the base of the segment that's adjacent in memory?