GNU C Library master sources branch master updated. glibc-2.25-240-g44e4b88

[fw at sourceware dot org]

This is an automated email from the git hooks/post-receive script. It was
generated because a ref change was pushed to the repository containing
the project "GNU C Library master sources".

The branch, master has been updated
       via  44e4b889ab0e0497567c8983ad25a78798a3ab51 (commit)
      from  832d8bc00b66adcb98a1c2064a2d555853ea49ed (commit)

Those revisions listed above that are new to this repository have
not appeared on any other notification email; so we list those
revisions in full, below.

- Log -----------------------------------------------------------------
http://sourceware.org/git/gitweb.cgi?p=glibc.git;a=commitdiff;h=44e4b889ab0e0497567c8983ad25a78798a3ab51

commit 44e4b889ab0e0497567c8983ad25a78798a3ab51
Author: Florian Weimer <fweimer@redhat.com>
Date:   Fri Apr 21 10:28:37 2017 +0200

    manual: Document replacing malloc [BZ #20424]

diff --git a/ChangeLog b/ChangeLog
index e60f6c3..dedd753 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2017-04-21  Florian Weimer  <fweimer@redhat.com>
+
+	[BZ #20424]
+	* manual/memory.texi (Replacing malloc): New section.
+	(Allocating Storage For Program Data): Reference it.
+	(The GNU Allocator): Likewise.
+
 2017-04-20  Joseph Myers  <joseph@codesourcery.com>
 
 	* stdlib/Versions (__strtod_internal): List explicitly, not as
diff --git a/manual/memory.texi b/manual/memory.texi
index a39cac8..a256ca0 100644
--- a/manual/memory.texi
+++ b/manual/memory.texi
@@ -167,6 +167,7 @@ special to @theglibc{} and GNU Compiler.
 * Unconstrained Allocation::    The @code{malloc} facility allows fully general
 		 		 dynamic allocation.
 * Allocation Debugging::        Finding memory leaks and not freed memory.
+* Replacing malloc::            Using your own @code{malloc}-style allocator.
 * Obstacks::                    Obstacks are less general than malloc
 				 but more efficient and convenient.
 * Variable Size Automatic::     Allocation of variable-sized blocks
@@ -299,6 +300,9 @@ A more detailed technical description of the GNU Allocator is maintained in
 the @glibcadj{} wiki. See
 @uref{https://sourceware.org/glibc/wiki/MallocInternals}.
 
+It is possible to use your own custom @code{malloc} instead of the
+built-in allocator provided by @theglibc{}.  @xref{Replacing malloc}.
+
 @node Unconstrained Allocation
 @subsection Unconstrained Allocation
 @cindex unconstrained memory allocation
@@ -1898,6 +1902,67 @@ from line 33 in the source file @file{/home/drepper/tst-mtrace.c} four
 times without freeing this memory before the program terminates.
 Whether this is a real problem remains to be investigated.
 
+@node Replacing malloc
+@subsection Replacing @code{malloc}
+
+@cindex @code{malloc} replacement
+@cindex @code{LD_PRELOAD} and @code{malloc}
+@cindex alternative @code{malloc} implementations
+@cindex customizing @code{malloc}
+@cindex interposing @code{malloc}
+@cindex preempting @code{malloc}
+@cindex replacing @code{malloc}
+@Theglibc{} supports replacing the built-in @code{malloc} implementation
+with a different allocator with the same interface.  For dynamically
+linked programs, this happens through ELF symbol interposition, either
+using shared object dependencies or @code{LD_PRELOAD}.  For static
+linking, the @code{malloc} replacement library must be linked in before
+linking against @code{libc.a} (explicitly or implicitly).
+
+@strong{Note:} Failure to provide a complete set of replacement
+functions (that is, all the functions used by the application,
+@theglibc{}, and other linked-in libraries) can lead to static linking
+failures, and, at run time, to heap corruption and application crashes.
+
+The minimum set of functions which has to be provided by a custom
+@code{malloc} is given in the table below.
+
+@table @code
+@item malloc
+@item free
+@item calloc
+@item realloc
+@end table
+
+These @code{malloc}-related functions are required for @theglibc{} to
+work.@footnote{Versions of @theglibc{} before 2.25 required that a
+custom @code{malloc} defines @code{__libc_memalign} (with the same
+interface as the @code{memalign} function).}
+
+The @code{malloc} implementation in @theglibc{} provides additional
+functionality not used by the library itself, but which is often used by
+other system libraries and applications.  A general-purpose replacement
+@code{malloc} implementation should provide definitions of these
+functions, too.  Their names are listed in the following table.
+
+@table @code
+@item aligned_alloc
+@item malloc_usable_size
+@item memalign
+@item posix_memalign
+@item pvalloc
+@item valloc
+@end table
+
+In addition, very old applications may use the obsolete @code{cfree}
+function.
+
+Further @code{malloc}-related functions such as @code{mallopt} or
+@code{mallinfo} will not have any effect or return incorrect statistics
+when a replacement @code{malloc} is in use.  However, failure to replace
+these functions typically does not result in crashes or other incorrect
+application behavior, but may result in static linking failures.
+
 @node Obstacks
 @subsection Obstacks
 @cindex obstacks

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog          |    7 +++++
 manual/memory.texi |   65 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+), 0 deletions(-)


hooks/post-receive
-- 
GNU C Library master sources