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Diffstat (limited to 'share')
| -rw-r--r-- | share/man/man9/malloc.9 | 40 |
1 files changed, 39 insertions, 1 deletions
diff --git a/share/man/man9/malloc.9 b/share/man/man9/malloc.9 index 146ba247ff0..966f08f7ddd 100644 --- a/share/man/man9/malloc.9 +++ b/share/man/man9/malloc.9 @@ -1,4 +1,4 @@ -.\" $OpenBSD: malloc.9,v 1.8 1999/10/05 20:53:11 aaron Exp $ +.\" $OpenBSD: malloc.9,v 1.9 2000/06/06 20:18:54 art Exp $ .\" $NetBSD: malloc.9,v 1.2 1996/10/30 05:29:54 lukem Exp $ .\" .\" Copyright (c) 1996 The NetBSD Foundation, Inc. @@ -386,3 +386,41 @@ panic: .It .Dq Data modified on freelist: Aq data object description .El +.Sh DEBUGGING +A kernel compiled with the +.Dv MALLOC_DEBUG +option allows for more extensive +debugging of memory allocations. You can choose which allocation to debug +with the +.Va malloc_deb_type +and +.Va malloc_deb_size +variables. +.Va malloc_deb_type +should be set to the memory type and +.Va malloc_deb_size +should be set to the memory size you want to debug. 0 can be used as a +wildcard. +.Pp +Every call to +.Fn malloc +with a memory type and size that matches the debugged type and size will +allocate two virtual pages. The pointer returned will be aligned so that +the requested area will end at the page boundary and the second virtual page +will be left unmapped. This way we can catch reads and writes outside the +allocated area. +.Pp +Every call to +.Fn free +with memory that was returned by the debugging malloc will cause the memory +area to become unmapped so that we can catch dangling reads and writes to +freed memory. +.Pp +There are no special diagnotics if any errors are caught by the debugging +malloc. The errors will look like normal access to unmapped memory. +.Pp +You have to be very careful when using the +.Dv MALLOC_DEBUG +option, the memory consumption can run away pretty quickly and there is +a severe performance degradation when allocating and freeing debugged memory +types. |