Re: [PATCH] zero-size E820 memory (kernel start-up failure)

From: Alexander Achenbach (achen@t-online.de)
Date: Sat Dec 21 2002 - 05:48:41 EST


Hi again.

Dave Jones wrote:
>
> > The patch adds code to remove empty entries before sorting regions. It
> > was generated for a 2.4.20 kernel.
>
> Looks good to me. Care to do a similar patch for 2.5 ?

This is it, to be applied against 2.5.52.
I've tested the kernel on an EPOX 4BEA-R and it boots as it should.

Cheers,
Alex

diff -ru linux-2.5.52/arch/i386/kernel/setup.c linux-2.5.52-nullmem/arch/i386/kernel/setup.c
--- linux-2.5.52/arch/i386/kernel/setup.c Mon Dec 16 03:07:56 2002
+++ linux-2.5.52-nullmem/arch/i386/kernel/setup.c Fri Dec 20 15:48:35 2002
@@ -14,6 +14,9 @@
  * Moved CPU detection code to cpu/${cpu}.c
  * Patrick Mochel <mochel@osdl.org>, March 2002
  *
+ * Provisions for empty E820 memory regions (reported by certain BIOSes).
+ * Alex Achenbach <xela@slit.de>, December 2002.
+ *
  */
 
 /*
@@ -275,7 +278,7 @@
         int chgidx, still_changing;
         int overlap_entries;
         int new_bios_entry;
- int old_nr, new_nr;
+ int old_nr, new_nr, chg_nr;
         int i;
 
         /*
@@ -329,20 +332,24 @@
         for (i=0; i < 2*old_nr; i++)
                 change_point[i] = &change_point_list[i];
 
- /* record all known change-points (starting and ending addresses) */
+ /* record all known change-points (starting and ending addresses),
+ omitting those that are for empty memory regions */
         chgidx = 0;
         for (i=0; i < old_nr; i++) {
- change_point[chgidx]->addr = biosmap[i].addr;
- change_point[chgidx++]->pbios = &biosmap[i];
- change_point[chgidx]->addr = biosmap[i].addr + biosmap[i].size;
- change_point[chgidx++]->pbios = &biosmap[i];
+ if (biosmap[i].size != 0) {
+ change_point[chgidx]->addr = biosmap[i].addr;
+ change_point[chgidx++]->pbios = &biosmap[i];
+ change_point[chgidx]->addr = biosmap[i].addr + biosmap[i].size;
+ change_point[chgidx++]->pbios = &biosmap[i];
+ }
         }
+ chg_nr = chgidx; /* true number of change-points */
 
         /* sort change-point list by memory addresses (low -> high) */
         still_changing = 1;
         while (still_changing) {
                 still_changing = 0;
- for (i=1; i < 2*old_nr; i++) {
+ for (i=1; i < chg_nr; i++) {
                         /* if <current_addr> > <last_addr>, swap */
                         /* or, if current=<start_addr> & last=<end_addr>, swap */
                         if ((change_point[i]->addr < change_point[i-1]->addr) ||
@@ -365,7 +372,7 @@
         last_type = 0; /* start with undefined memory type */
         last_addr = 0; /* start with 0 as last starting address */
         /* loop through change-points, determining affect on the new bios map */
- for (chgidx=0; chgidx < 2*old_nr; chgidx++)
+ for (chgidx=0; chgidx < chg_nr; chgidx++)
         {
                 /* keep track of all overlapping bios entries */
                 if (change_point[chgidx]->addr == change_point[chgidx]->pbios->addr)

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