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fold the contents of malloc.conf.5 into malloc.3 and sysctl.2,

now that there is essentially no malloc.conf;
text tweaked by deraadt; ok otto deraadt
OPENBSD_6_5
jmc 6 years ago
parent
commit
a53bba0f97
1 changed files with 118 additions and 6 deletions
  1. +118
    -6
      src/lib/libc/stdlib/malloc.3

+ 118
- 6
src/lib/libc/stdlib/malloc.3 View File

@ -30,7 +30,7 @@
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" $OpenBSD: malloc.3,v 1.120 2018/11/21 06:57:04 otto Exp $
.\" $OpenBSD: malloc.3,v 1.121 2018/11/21 09:22:58 jmc Exp $
.\"
.Dd $Mdocdate: November 21 2018 $
.Dt MALLOC 3
@ -234,6 +234,115 @@ If
is not a multiple of
.Fa alignment ,
behavior is undefined.
.Sh MALLOC OPTIONS
Upon the first call to the
.Fn malloc
family of functions, an initialization sequence inspects the
value of the
.Va vm.malloc_conf
.Xr sysctl 2 ,
next checks the environment for a variable called
.Ev MALLOC_OPTIONS ,
and finally looks at the global variable
.Va malloc_options
in the program.
Each is scanned for the flags documented below.
Unless otherwise noted uppercase means on, lowercase means off.
.Bl -tag -width indent
.It Cm C
.Dq Canaries .
Add canaries at the end of allocations in order to detect
heap overflows.
The canary's content is checked when
.Nm free
is called.
If it has been corrupted, the process is aborted.
.It Cm D
.Dq Dump .
.Fn malloc
will dump statistics to the file
.Pa ./malloc.out ,
if it already exists,
at exit.
This option requires the library to have been compiled with -DMALLOC_STATS in
order to have any effect.
.It Cm F
.Dq Freecheck .
Enable more extensive double free and use after free detection.
All chunks in the delayed free list will be checked for double frees.
Unused pages on the freelist are read and write protected to
cause a segmentation fault upon access.
.It Cm G
.Dq Guard .
Enable guard pages.
Each page size or larger allocation is followed by a guard page that will
cause a segmentation fault upon any access.
.It Cm J
.Dq More junking .
Increase the junk level by one if it is smaller than 2.
.It Cm j
.Dq Less junking .
Decrease the junk level by one if it is larger than 0.
Junking writes some junk bytes into the area allocated.
Junk is bytes of 0xdb when allocating;
freed chunks are filled with 0xdf.
By default the junk level is 1: after free,
small chunks are completely junked;
for pages the first part is junked.
After a delay,
the filling pattern is validated and the process is aborted if the pattern
was modified.
For junk level 2, junking is done on allocation as well and without size
restrictions.
If the junk level is zero, no junking is performed.
.It Cm R
.Dq realloc .
Always reallocate when
.Fn realloc
is called, even if the initial allocation was big enough.
.\".Pp
.\".It Cm U
.\".Dq utrace .
.\"Generate entries for
.\".Xr ktrace 1
.\"for all operations.
.\"Consult the source for this one.
.It Cm S
Enable all options suitable for security auditing.
.It Cm U
.Dq Free unmap .
Enable use after free protection for larger allocations.
Unused pages on the freelist are read and write protected to
cause a segmentation fault upon access.
.It Cm X
.Dq xmalloc .
Rather than return failure,
.Xr abort 3
the program with a diagnostic message on stderr.
It is the intention that this option be set at compile time by
including in the source:
.Bd -literal -offset indent
extern char *malloc_options;
malloc_options = "X";
.Ed
.Pp
Note that this will cause code that is supposed to handle
out-of-memory conditions gracefully to abort instead.
.It Cm <
.Dq Halve the cache size .
Decrease the size of the free page cache by a factor of two.
.It Cm >
.Dq Double the cache size .
Increase the size of the free page cache by a factor of two.
.El
.Pp
If a program changes behavior if any of these options (except
.Cm X )
are used,
it is buggy.
.Pp
The default number of free pages cached is 64 per malloc pool.
Multi-threaded programs use multiple pools.
.Sh RETURN VALUES
Upon successful completion, the allocation functions
return a pointer to the allocated space; otherwise,
@ -404,8 +513,7 @@ Deallocation of such an object should be done by calling
.Sh ENVIRONMENT
.Bl -tag -width "MALLOC_OPTIONS"
.It Ev MALLOC_OPTIONS
String of flags documented in
.Xr malloc.conf 5 .
String of option flags.
.El
.Sh EXAMPLES
If
@ -460,6 +568,11 @@ or at the cost of initialization:
if ((p = calloc(num, size)) == NULL)
err(1, NULL);
.Ed
.Pp
Set a systemwide reduction of the cache to a quarter of the
default size and use guard pages:
.Pp
.Dl # sysctl vm.malloc_conf='G<<'
.Sh DIAGNOSTICS
If any of the functions detect an error condition,
a message will be printed to file descriptor
@ -525,11 +638,10 @@ consult sources and/or wizards.
.Xr brk 2 ,
.Xr mmap 2 ,
.Xr munmap 2 ,
.Xr sysctl 2 ,
.Xr alloca 3 ,
.Xr getpagesize 3 ,
.Xr posix_memalign 3 ,
.Xr sysconf 3 ,
.Xr malloc.conf 5
.Xr posix_memalign 3
.Sh STANDARDS
The
.Fn malloc ,


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