Add note on free list pointers overwriting M_PERTURB bytes

Fixes BZ #12140.
git-mirror · Oct 18, 2012 · b741de2 · b741de2
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diff --git a/ChangeLog b/ChangeLog
@@ -1,3 +1,10 @@
+2012-10-18  Siddhesh Poyarekar  <siddhesh@redhat.com>
+
+	[BZ #12140]
+	* manual/memory.texi (Malloc Tunable Parameters): Add note
+	about free list pointers overwriting some perturb bytes.
+	Wording suggested by Roland McGrath.
+
 2012-10-17  Joseph Myers  <joseph@codesourcery.com>
 
 	* math/libm-test.inc (gamma_test): Do not call feclearexcept.

diff --git a/NEWS b/NEWS
@@ -10,13 +10,13 @@ Version 2.17
 * The following bugs are resolved with this release:
 
   1349, 3479, 5044, 5298, 5400, 6530, 6778, 6808, 9685, 9914, 10014, 10038,
-  10631, 11438, 11607, 13412, 13542, 13629, 13679, 13696, 13717, 13741,
-  13939, 13966, 14042, 14090, 14150, 14151, 14154, 14157, 14166, 14173,
-  14195, 14237, 14251, 14252, 14283, 14298, 14303, 14307, 14328, 14331,
-  14336, 14337, 14347, 14349, 14376, 14417, 14459, 14476, 14477, 14505,
-  14510, 14516, 14518, 14519, 14530, 14532, 14538, 14543, 14544, 14545,
-  14557, 14562, 14568, 14576, 14579, 14583, 14587, 14602, 14621, 14638,
-  14645, 14648, 14652, 14660, 14661, 14716.
+  10631, 11438, 11607, 12140, 13412, 13542, 13629, 13679, 13696, 13717,
+  13741, 13939, 13966, 14042, 14090, 14150, 14151, 14154, 14157, 14166,
+  14173, 14195, 14237, 14251, 14252, 14283, 14298, 14303, 14307, 14328,
+  14331, 14336, 14337, 14347, 14349, 14376, 14417, 14459, 14476, 14477,
+  14505, 14510, 14516, 14518, 14519, 14530, 14532, 14538, 14543, 14544,
+  14545, 14557, 14562, 14568, 14576, 14579, 14583, 14587, 14602, 14621,
+  14638, 14645, 14648, 14652, 14660, 14661, 14716.
 
 * Support for STT_GNU_IFUNC symbols added for s390 and s390x.
   Optimized versions of memcpy, memset, and memcmp added for System z10 and

diff --git a/manual/memory.texi b/manual/memory.texi
@@ -706,7 +706,10 @@ to zero disables all use of @code{mmap}.
 If non-zero, memory blocks are filled with values depending on some
 low order bits of this parameter when they are allocated (except when
 allocated by @code{calloc}) and freed.  This can be used to debug the
-use of uninitialized or freed heap memory.
+use of uninitialized or freed heap memory.  Note that this option does not
+guarantee that the freed block will have any specific values.  It only
+guarantees that the content the block had before it was freed will be
+overwritten.
 @end table
 
 @end deftypefun