z_os_notes

减少内存碎片的malloc分配函数

[ From Tony Reyelts. ]

Building dmalloc on z/OS 1.3

   After a few tries, I've boiled down the steps to building dmalloc
   on z/OS to run under USS. Here's how:

   1. Set the environment so Makefile generates a valid compile:

         export DEFINES='-D_XOPEN_SOURCE_EXTENDED -Wc,"LANGLVL(ANSI)"

   2. Run configure:

         configure --prefix==/some/path --disable-cxx

      Note: The default is to use C++, but the make failed with it
      because the compiler expects the extension .C, not .cc. Since I
      don't use C++, I disabled that part.

      You'll get the following message from configure:

         WARNING: The library has limited support for heaps
         that grow down.  Please see the NOTES file and
         send the author mail.

   3. Edit conf.h:

      - Change HEAP_GROWS_UP to 1 from 0. For some reason, configure
        thinks it grows down when it really doesn't.

   4. Edit the Makefile:

      - Unset $LIBS because cc won't link with it on the end of the
        link command.

      - Set LDFLAGS to "-L ./" so libdmalloc.a can be found.

   5. Create a dummy ranlib (return 0) because z/OS doesn't have one.

   6. Run make to build the code.

      I got a compile warning for malloc.c assigning between "long *"
      and "unsigned long *" at line 246. It looks like this is because
      _dmalloc_address_seen_n (unsigned long *) is being passed as the
      third argument to _dmalloc_environ_get (long *). The code seems to
      work ok, so I didn't bother fixing this.

Using dmalloc on z/OS 1.3

   1. dmalloc uses sbrk() to allocate storage. The sbrk() function on
      z/OS only uses the primary allocation (vs. secondary), so the
      primary has to be set to be big enough to hold eveything.

      This is a Language Environment run-time option called HEAP. In
      USS, you can set it with the _CEE_RUNOPTS environment variable.
      For example, I used the following:

          export_CEE_RUNOPTS="heap(64M,1M,ANY,FREE)"

   2. The z/OS C compiler provides functions for doing MVS-specific
      things such as allocating data sets. The easiest way to gain access
      is to compile with -Wc,"LANGLVL(EXTENDED)" vs. -Wc,"LANGLVL(ANSI)".
      This makes dmalloc.h think it is a non-ANSI compile (__STDC__ is not
      set), so the definitions of malloc(), etc fall afoul of those from
      stdlib.h. So, if you're using LANGLVL(EXTENDED), you'll need to
      edit dmalloc.h so the ANSI version of DMALLOC_PNT is used.

   3. The following functions are known to not be tracked by dmalloc on
      z/OS 1.3. They apparently use their own storage scheme:

         - glob()/globfree()
         - wordexp()/wordfree()