Bug 20102

Summary:	malloc(3) should document MALLOC_PERTURB_ env option
Product:	Documentation	Reporter:	Mike Frysinger (vapier)
Component:	man-pages	Assignee:	Michael Kerrisk (mtk.manpages)
Status:	RESOLVED CODE_FIX
Severity:	normal	CC:	mtk.manpages
Priority:	P1
Hardware:	All
OS:	Linux
Kernel Version:		Subsystem:
Regression:	No	Bisected commit-id:

Description Mike Frysinger 2010-10-11 19:00:13 UTC

setting MALLOC_PERTURB_ in the env will take that number and initialize all malloc's with that value (and the inverse when freeing).  this should be documented in malloc(3) (and noted in free(3)).

e.g. if you set MALLOC_PERTURB_=123, glibc will do memset((123 ^ 0xff) & 0xff) when doing malloc(), and then glibc will do memset(123 & 0xff) when doing free()

Comment 1 Michael Kerrisk 2010-10-23 12:31:55 UTC

Mike,

Thanks for the heads-up on this. Looking closer, there are a bunch of these environment variables that are undocumented, and they're also closely related to the mallopt() library function, which is also undocumented. I think it would be best to document all of this stuff together, and best done on a mallopt(3) page, rather that in the existing malloc(3). (And yes, the MALLOC_TRACE_ info that is currently in mallopt(3) should probably also move to the to-be-created mallopt(3) page.) I'll get onto this.

Thanks,

Michael

Comment 2 Michael Kerrisk 2012-04-14 20:54:29 UTC

man-pages-3.38 added mallopt(3) page which covers MALLOC_PERTURB_ and other malloc-related environment variables. With respect to mentions in malloc(3) and free(3), I've elected simply to use SEE ALSO.

For 3.39, I've just fixed a small error in the discussion of M_PERTURB and free().