[Crash-utility] [PATCH] Crash-Utility: s390x: Auto-detect the correct MAX_PHYSMEM_BITS used in vmcore being analyzed.

[Dave Anderson]

----- Original Message -----
> 
> And complicating matters even further, your patch presumes that the
> kernel has configured CONFIG_SPARSEMEM_EXTREME in conjunction with
> CONFIG_SPARSEMEM.  Would it be possible for an s390x to be configured
> with just CONFIG_SPARSEMEM alone?  If so, your patch breaks down.
> 
> Or is there another way you can determine which MAX_PHYSMEM_BITS value
> is in use?
> 
> Dave
> 

Using your scheme, this is the best I can come up with (untested):

--- s390x.c     10 Nov 2011 14:37:15 -0000      1.57
+++ s390x.c     21 Dec 2011 17:07:20 -0000
@@ -282,6 +282,43 @@
        }
 }
 
+static int
+set_s390x_max_physmem_bits(void)
+{
+       int array_len, dimension;
+
+       if (!kernel_symbol_exists("mem_section"))
+               return TRUE;
+
+       if (!(array_len = get_array_length("mem_section", &dimension, 0))
+               return FALSE;
+
+       /*
+        * If not CONFIG_SPARSEMEM_EXTREME, presume the older 42.
+        */
+       if (dimension) { 
+               machdep->max_physmem_bits = _MAX_PHYSMEM_BITS_OLD;
+               return TRUE;
+       }
+
+       /*
+        * The older s390x kernels uses _MAX_PHYSMEM_BITS as 42 and the
+        * newer kernels uses 46 bits.
+        */
+       STRUCT_SIZE_INIT(mem_section, "mem_section");
+       machdep->max_physmem_bits = _MAX_PHYSMEM_BITS_OLD;
+       if ((array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT_EXTREME()))
+               || (array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT())))
+               return TRUE;
+
+       machdep->max_physmem_bits = _MAX_PHYSMEM_BITS_NEW;
+       if ((array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT_EXTREME()))
+               || (array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT())))
+               return TRUE;
+
+       return FALSE;
+}
+
 /*
  *  Do all necessary machine-specific setup here.  This is called several
  *  times during initialization.
@@ -350,7 +387,8 @@
                if (!machdep->hz)
                        machdep->hz = HZ;
                machdep->section_size_bits = _SECTION_SIZE_BITS;
-               machdep->max_physmem_bits = _MAX_PHYSMEM_BITS;
+               if (!set_s390x_max_physmem_bits())
+                       error(FATAL, "cannot determine MAX_PHYSMEM_BITS");
                s390x_offsets_init();
                break;