Bug 203254 - Avoid MAP_FIXED in aspacemgr
Summary: Avoid MAP_FIXED in aspacemgr
Status: ASSIGNED
Alias: None
Product: valgrind
Classification: Developer tools
Component: general (show other bugs)
Version: 3.5 SVN
Platform: Unlisted Binaries macOS
: NOR normal
Target Milestone: blocking3.6.0
Assignee: Julian Seward
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2009-08-10 03:56 UTC by Nicholas Nethercote
Modified: 2009-08-10 03:57 UTC (History)
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Description Nicholas Nethercote 2009-08-10 03:56:45 UTC 
This is a follow-on from bug 192634.  Valgrind's address space manager current uses MAP_FIXED a lot.  This relies on having a perfect view of the address space layout.  This is feasible on Linux, but a problem on Darwin, as the Darwin kernel tends to add mappings in ways that a user program cannot easily observe.  Valgrind currently checks for such kernel mappings at various points, but this is slow, and we may be missing some cases, in which case Valgrind will trash kernel mappings occasionally on Darwin.  So it's both a correctness and performance issue.

To fix this requires reworking aspacemgr to greatly reduce or preferably avoid MAP_FIXED completely.