savecore doesn't really work with alternate system image

[Jeff Mogul]

Description:
	Savecore takes an optional argument to specify a file besides
	/vmunix as the system that was running when a crash dump
	was made.  This does not work properly, because savecore
	uses the namelist from /vmunix even if an alternate system
	is specified, and so unless the systems are almost identical
	it decides that the crash dump has a bad magic number and
	fails to save it.
Repeat-By:
	Configure a system differently from the one you normally run;
	make sure that the address of the variable _dumpmag is different.
	Call the new kernel /newvmunix; do NOT replace /vmunix
	
	boot /newvmunix and make it crash (with a dump.)
	
	boot /vmunix single-user, mount the appropriate filesystems,
	and type

	# /etc/savecore /usr/crash /newvmunix

	No core dump will be saved.
Fix:
	One cannot fix this simply by having savecore read the namelist
	from the alternate system instead of /vmunix; this is because
	the program wants to compare values from the dump and from /dev/kmem.
	So, we need to use two copies of the namelist and change the
	appropriate references in the code to use one or the other.

	Note that the alternate system must still use the same dump
	partition and size as /vmunix uses (you'd be a fool if you
	tried to do otherwise.)
	
	The "diff" listing given below also includes code for an additional
	"-v" command-line flag, to make savecore a little more verbose
	about why it rejects a crash dump.

diff savecore.c.old savecore.c
7a8,16
> 
> /*
>  * HISTORY:
>  * 20 June 1984	Jeff Mogul	Stanford
>  *	- Works properly with optional "system" argument (original
>  *	version assumed identical offsets into /dev/kmem and dump.)
>  *	- -v flag for more verbose output
>  */
> 
28c37
< struct nlist nl[] = {
---
> struct nlist current_nl[] = {	/* namelist for currently running system */
45a55,65
> struct nlist dump_nl[] = {	/* name list for dumped system */
> 	{ "_dumpdev" },		/* entries MUST be the same as */
> 	{ "_dumplo" },		/*	those in current_nl[]  */
> 	{ "_time" },
> 	{ "_dumpsize" },
> 	{ "_version" },
> 	{ "_panicstr" },
> 	{ "_dumpmag" },
> 	{ "" },
> };
> 
64a85
> int	Verbose;
70a92,107
> 	while ((argc > 1) && (argv[1][0] == '-')) {
> 		switch (argv[1][1]) {
> 		case 'v':
> 			Verbose = 1;
> 			break;
> 		default:
> 			fprintf(stderr, "savecore: illegal flag -%c\n",
> 				argv[1][1]);
> 			fprintf(stderr,
> 				"usage: savecore [-v] dirname [ system ]\n");
> 			exit(1);
> 		}
> 		argc--;
> 		argv++;
> 	}
> 
72c109
< 		fprintf(stderr, "usage: savecore dirname [ system ]\n");
---
> 		fprintf(stderr, "usage: savecore [-v] dirname [ system ]\n");
90c127,129
< 		} else
---
> 		} else {
> 			if (Verbose)
> 				fprintf(stderr, "No space or time\n");
91a131
> 		}
92a133,135
> 	else if (Verbose) {
> 		fprintf(stderr, "No dump exists\n");
> 	}
103c146
< 	Lseek(dumpfd, (off_t)(dumplo + ok(nl[X_DUMPMAG].n_value)), 0);
---
> 	Lseek(dumpfd, (off_t)(dumplo + ok(dump_nl[X_DUMPMAG].n_value)), 0);
105a149,152
> 	if (Verbose && (word != dumpmag)) {
> 		printf("dumplo = %d (%d bytes)\n", dumplo/512, dumplo);
> 		printf("magic number mismatch: %x != %x\n", word, dumpmag);
> 	}
115c162
< 	Lseek(dumpfd, (off_t)(dumplo + ok(nl[X_DUMPMAG].n_value)), 0);
---
> 	Lseek(dumpfd, (off_t)(dumplo + ok(dump_nl[X_DUMPMAG].n_value)), 0);
158a206,208
> 	char *dump_sys;
> 	
> 	dump_sys = system ? system : "/vmunix";
160,161c210,221
< 	nlist("/vmunix", nl);
< 	if (nl[X_DUMPDEV].n_value == 0) {
---
> 	nlist("/vmunix", current_nl);
> 	nlist(dump_sys, dump_nl);
> 
> 	/*
> 	 * Some names we need for the currently running system,
> 	 * others for the system that was running when the dump was made.
> 	 * The values obtained from the current system are used
> 	 * to look for things in /dev/kmem that cannot be found
> 	 * in the dump_sys namelist, but are presumed to be the same
> 	 * (since the disk partitions are probably the same!)
> 	 */
> 	if (current_nl[X_DUMPDEV].n_value == 0) {
165c225
< 	if (nl[X_DUMPLO].n_value == 0) {
---
> 	if (current_nl[X_DUMPLO].n_value == 0) {
169,170c229,231
< 	if (nl[X_TIME].n_value == 0) {
< 		fprintf(stderr, "savecore: /vmunix: time not in namelist\n");
---
> 	if (dump_nl[X_TIME].n_value == 0) {
> 		fprintf(stderr, "savecore: %s: time not in namelist\n",
> 				dump_sys);
173,174c234,236
< 	if (nl[X_DUMPSIZE].n_value == 0) {
< 		fprintf(stderr, "savecore: /vmunix: dumpsize not in namelist\n");
---
> 	if (dump_nl[X_DUMPSIZE].n_value == 0) {
> 		fprintf(stderr, "savecore: %s: dumpsize not in namelist\n",
> 				dump_sys);
177,178c239,242
< 	if (nl[X_VERSION].n_value == 0) {
< 		fprintf(stderr, "savecore: /vmunix: version not in namelist\n");
---
> 	/* we need VERSION in both images */
> 	if (current_nl[X_VERSION].n_value == 0) {
> 		fprintf(stderr, "savecore: /vmunix: version not in namelist\n",
> 				dump_sys);
181,182c245,247
< 	if (nl[X_PANICSTR].n_value == 0) {
< 		fprintf(stderr, "savecore: /vmunix: panicstr not in namelist\n");
---
> 	if (dump_nl[X_VERSION].n_value == 0) {
> 		fprintf(stderr, "savecore: %s: version not in namelist\n",
> 				dump_sys);
185c250,256
< 	if (nl[X_DUMPMAG].n_value == 0) {
---
> 	if (dump_nl[X_PANICSTR].n_value == 0) {
> 		fprintf(stderr, "savecore: %s: panicstr not in namelist\n",
> 				dump_sys);
> 		exit(1);
> 	}
> 	/* we need DUMPMAG in both images */
> 	if (current_nl[X_DUMPMAG].n_value == 0) {
188a260,264
> 	if (dump_nl[X_DUMPMAG].n_value == 0) {
> 		fprintf(stderr, "savecore: %s: dumpmag not in namelist\n",
> 				dump_sys);
> 		exit(1);
> 	}
190c266
< 	Lseek(kmem, (long)nl[X_DUMPDEV].n_value, 0);
---
> 	Lseek(kmem, (long)current_nl[X_DUMPDEV].n_value, 0);
192c268
< 	Lseek(kmem, (long)nl[X_DUMPLO].n_value, 0);
---
> 	Lseek(kmem, (long)current_nl[X_DUMPLO].n_value, 0);
194c270
< 	Lseek(kmem, (long)nl[X_DUMPMAG].n_value, 0);
---
> 	Lseek(kmem, (long)current_nl[X_DUMPMAG].n_value, 0);
204c280
< 	fseek(fp, (long)nl[X_VERSION].n_value, 0);
---
> 	fseek(fp, (long)current_nl[X_VERSION].n_value, 0);
218c294
< 	fseek(fp, (off_t)(dumplo+ok(nl[X_VERSION].n_value)), 0);
---
> 	fseek(fp, (off_t)(dumplo+ok(dump_nl[X_VERSION].n_value)), 0);
221c297
< 	if (!eq(vers, core_vers))
---
> 	if (!eq(vers, core_vers) && (system == 0))
226c302
< 	fseek(fp, (off_t)(dumplo + ok(nl[X_PANICSTR].n_value)), 0);
---
> 	fseek(fp, (off_t)(dumplo + ok(dump_nl[X_PANICSTR].n_value)), 0);
246c322
< 	Lseek(dumpfd, (off_t)(dumplo + ok(nl[X_TIME].n_value)), 0);
---
> 	Lseek(dumpfd, (off_t)(dumplo + ok(dump_nl[X_TIME].n_value)), 0);
249c325,327
< 	if (dumptime == 0)
---
> 	if (dumptime == 0) {
> 		if (Verbose)
> 			printf("dump time not found\n");
250a329
> 	}
333c412
< 	Lseek(ifd, (off_t)(dumplo + ok(nl[X_DUMPSIZE].n_value)), 0);
---
> 	Lseek(ifd, (off_t)(dumplo + ok(dump_nl[X_DUMPSIZE].n_value)), 0);