From 841f1110dd6180f69bfb19a1a22d12d52660dc04 Mon Sep 17 00:00:00 2001
From: David du Colombier <0intro@gmail.com>
Date: Sun, 14 Aug 1994 00:00:00 +0000
Subject: [PATCH] Plan 9 from Bell Labs 1994-08-14

---
 pc/dat.h       |   1 -
 pc/main.c      | 105 ++++++++++++++++++++++++++++++++-----------------
 pc/trap.c      |   4 ++
 port/devproc.c |  10 +++++
 port/portdat.h |   3 ++
 5 files changed, 86 insertions(+), 37 deletions(-)

diff --git a/pc/dat.h b/pc/dat.h
index 7c18da9cd489f8f750343770fa3c1e57b229bd02..0ccf03e826f138c9a438fd3f7165e14386f03ef3 100644
--- a/pc/dat.h
+++ b/pc/dat.h
@@ -195,4 +195,3 @@ extern int	cpuflag;		/* true if this is a CPU */
 extern Mach	*m;
 extern Proc	*up;
 extern char	filaddr[];
-extern ulong	crasharea;
diff --git a/pc/main.c b/pc/main.c
index adf43b795de4321f879d011bb605e9e2177c6579..e99b2f1e9c2a62c2a7c11c5611d3200e2928718d 100644
--- a/pc/main.c
+++ b/pc/main.c
@@ -31,7 +31,6 @@ char filaddr[NAMELEN];
 char *confname[MAXCONF];
 char *confval[MAXCONF];
 int nconf;
-ulong crasharea;
 
 /* memory map */
 #define MAXMEG 64
@@ -64,7 +63,6 @@ main(void)
 	chandevreset();
 	swapinit();
 	userinit();
-conf.npage0 += CRASHSIZE;
 	schedinit();
 }
 
@@ -282,13 +280,48 @@ getconf(char *name)
 	return 0;
 }
 
+/*
+ *  zero memory to set ECC.
+ *  do a quick memory test also.
+ *
+ *  if any part of a meg is missing/broken, drop the whole meg.
+ */
+int
+memclrtest(int meg, int len, long seed)
+{
+	int j, n;
+	long y;
+	long *lp;
+	
+	for(j = 0; j < len; j += BY2PG){
+		lp = mapaddr(KZERO|(meg*MB+j));
+		for(n = 0; n < BY2PG/BY2WD; n++)
+			lp[n] = seed + n;
+	}
+	for(j = 0; j < len; j += BY2PG){
+		lp = mapaddr(KZERO|(meg*MB+j));
+		for(n = 0; n < BY2PG/(2*BY2WD); n++){
+			y = lp[n];
+			lp[n] = ~lp[n^((BY2PG/BY2WD)-1)];
+			lp[n^((BY2PG/BY2WD)-1)] = ~y;
+		}
+	}
+	for(j = 0; j < len; j += BY2PG){
+		lp = mapaddr(KZERO|(meg*MB+j));
+		for(n = 0; n < BY2PG/BY2WD; n++)
+			if(lp[n] != ~(seed + (n^((BY2PG/BY2WD)-1))))
+				return -1;
+		memset(lp, 0, BY2PG);
+	}
+	return 0;
+}
+
 void
 confinit(void)
 {
-	long x, y, i, j, n;
+	long x, i, j, n;
 	int pcnt;
 	ulong ktop;
-	long *lp;
 	char *cp;
 	char *line[MAXCONF];
 	extern int defmaxmsg;
@@ -320,11 +353,11 @@ confinit(void)
 			if(i < defmaxmsg && i >=128)
 				defmaxmsg = i;
 		}
-		/* HACK: where should this come from? */
 		if(strcmp(confname[nconf], "filaddr") == 0)
 			strcpy(filaddr, confval[nconf]);
 		nconf++;
 	}
+
 	/*
 	 *  size memory above 1 meg. Kernel sits at 1 meg.  We
 	 *  only recognize MB size chunks.
@@ -350,37 +383,30 @@ confinit(void)
 		/*
 		 *  check for correct value
 		 */
-		if(*mapaddr(KZERO|(i*MB)) == x && *mapaddr(KZERO|((i+1)*MB-BY2WD)) == x){
+		if(*mapaddr(KZERO|(i*MB)) == x && *mapaddr(KZERO|((i+1)*MB-BY2WD)) == x)
 			mmap[i] = 'x';
-			/*
-			 *  zero memory to set ECC but skip over the kernel
-			 *  do a quick memory test also
-			if(i != 1){
-				for(j = 0; j < MB/BY2PG; j += BY2PG){
-					lp = mapaddr(KZERO|(i*MB+j));
-					for(n = 0; n < BY2PG/BY2WD; n++)
-						lp[n] = x + n;
-				}
-				for(j = 0; j < MB/BY2PG; j += BY2PG){
-					lp = mapaddr(KZERO|(i*MB+j));
-					for(n = 0; n < BY2PG/(2*BY2WD); n++){
-						y = lp[n];
-						lp[n] = ~lp[n^((BY2PG/BY2WD)-1)];
-						lp[n^((BY2PG/BY2WD)-1)] = ~y;
-					}
-				}
-				for(j = 0; j < MB/BY2PG; j += BY2PG){
-					lp = mapaddr(KZERO|(i*MB+j));
-					for(n = 0; n < BY2PG/BY2WD; n++)
-						if(lp[n] != ~(x + (n^((BY2PG/BY2WD)-1))))
-							mmap[i] = ' ';
-					memset(lp, 0, BY2PG);
-				}
-			}
-			 */
+		x += 0x3141526;
+	}
+
+	/*
+	 *  zero and clear all except first 2 meg and crash area.
+	 *  put crash area at high end of memory.
+	 */
+	x = 0x12345678;
+	for(i = MAXMEG; i > 1; i--){
+		if(mmap[i] != 'x')
+			continue;
+		j = MB;
+		if(crasharea == 0){
+			crasharea = i*MB - CRASHSIZE;
+			crashend = crasharea + CRASHSIZE;
+			j = MB - CRASHSIZE;
 		}
+		if(memclrtest(i, j, x) < 0)
+			mmap[i] = ' ';
 		x += 0x3141526;
 	}
+
 	/*
 	 *  bank0 usually goes from the end of kernel bss to the end of memory
 	 */
@@ -389,12 +415,13 @@ confinit(void)
 	conf.base0 = ktop;
 	for(i = 1; mmap[i] == 'x'; i++)
 		;
-	conf.npage0 = (i*MB - ktop - CRASHSIZE)/BY2PG;
-	crasharea = KZERO|(conf.base0 + conf.npage0*BY2PG);
+	conf.npage0 = (i*MB - ktop)/BY2PG;
 	conf.topofmem = i*MB;
+	if(crasharea < conf.base0 + BY2PG*conf.npage0)
+		conf.npage0 -= PGROUND(CRASHSIZE)/BY2PG;
 
 	/*
-	 *  bank1 usually goes from the end of BOOTARGS to 640k - crash space
+	 *  bank1 usually goes from the end of BOOTARGS to 640k
 	 */
 	conf.base1 = (ulong)(BOOTARGS + BOOTARGSLEN);
 	conf.base1 = PGROUND(conf.base1);
@@ -402,7 +429,7 @@ confinit(void)
 	conf.npage1 = (640*1024 - conf.base1)/BY2PG;
 
 	/*
-	 *  if there is a hole in memory (due to a shadow BIOS) make the
+	 *  if there is a hole in memory (e.g. due to a shadow BIOS) make the
 	 *  memory after the hole be bank 1. The memory from 0 to 640k
 	 *  is lost.
 	 */
@@ -413,9 +440,15 @@ confinit(void)
 				;
 			conf.npage1 = (j - i)*MB/BY2PG;
 			conf.topofmem = j*MB;
+			if(crasharea < conf.base1 + BY2PG*conf.npage1)
+				conf.npage1 -= PGROUND(CRASHSIZE)/BY2PG;
 			break;
 		}
 
+	/* make crasharea a virtual address */
+	crasharea |= KZERO;
+	crashend |= KZERO;
+
 	conf.npage = conf.npage0 + conf.npage1;
 	conf.ldepth = 0;
 	if(pcnt < 10)
diff --git a/pc/trap.c b/pc/trap.c
index 14bd520c4df44e25d0e28fb6c45350e6df685a95..4c1d05ecc89365eae53bd78d6e9caeec4e1f2cef 100644
--- a/pc/trap.c
+++ b/pc/trap.c
@@ -364,6 +364,8 @@ dumpregs(Ureg *ur)
 	print("  ur %lux up %lux\n", ur, up);
 
 	/* save crash info */
+	if(crasharea == 0)
+		return;
 	print("crasharea 0x%lux\n", crasharea);
 	cs = (Crashstate*)crasharea;
 	memmove(&cs->ureg, ur, sizeof(Ureg));
@@ -396,6 +398,8 @@ dumpstack(void)
 	}
 
 	/* save crash info */
+	if(crasharea == 0)
+		return;
 	print("crasharea 0x%lux\n", crasharea);
 	cs = (Crashstate*)crasharea;
 	memmove(cs->kstack, up->kstack, KSTACK);
diff --git a/port/devproc.c b/port/devproc.c
index ab5855016514f4d493b856bbcf5023ae59ad8839..d17d8a94b7f2a40f2df3136d11dbc5f0b5e1d9ff 100644
--- a/port/devproc.c
+++ b/port/devproc.c
@@ -49,6 +49,10 @@ Dirtab procdir[] =
 /* Segment type from portdat.h */
 char *sname[]={ "Text", "Data", "Bss", "Stack", "Shared", "Phys", "Shdata" };
 
+/* where to put crash information when memory isn't wiped */
+ulong crasharea;
+ulong crashend;
+
 /*
  * Qids are, in path:
  *	 4 bits of file type (qids above)
@@ -314,6 +318,12 @@ procread(Chan *c, void *va, long n, ulong offset)
 			memmove(a, (char*)offset, n);
 			return n;
 		}
+		if(offset >= crasharea && offset < crashend){
+			if(offset+n > crashend)
+				n = crashend - offset;
+			memmove(a, (char*)offset, n);
+			return n;
+		}
 		error(Ebadarg);
 
 	case Qnote:
diff --git a/port/portdat.h b/port/portdat.h
index 91fa531a43ac1185bfea149c6ef9041edef282e5..99697c75369f806534ee98b4667c8b26572dcc85 100644
--- a/port/portdat.h
+++ b/port/portdat.h
@@ -697,5 +697,8 @@ enum
 extern int mouseshifted;
 extern int mousetype;
 extern int mouseswap;
+
 extern int nsyscall;
 extern Physseg physseg[];
+extern ulong crasharea;
+extern ulong crashend;