Fix for the "snap.so" extension module to pass the value of the ARM64

"kimage_voffset" value in the ELF header.  Without the patch, it is
necessary to use the "--machdep kvimage_offset=<value>" command line
option, or the session fails with the message "crash: vmlinux and
vmcore do not match!".
([email protected])

Author: Dave Anderson

extensions/snap.c

@@ -425,7 +425,7 @@ generate_elf_header(int type, int fd, char *filename)
 	struct node_table *nt;
 	struct SNAP_info {
 		ulonglong task_struct;
-		ulonglong relocate;
+		ulonglong arch_data;
 	} SNAP_info;
 
 	num_segments = vt->numnodes;
@@ -610,7 +610,13 @@ generate_elf_header(int type, int fd, char *filename)
 
   	/* NT_TASKSTRUCT note */
 	SNAP_info.task_struct = CURRENT_TASK();
-	SNAP_info.relocate = kt->relocate;
+#ifdef X86_64
+	SNAP_info.arch_data = kt->relocate;
+#elif ARM64
+	SNAP_info.arch_data = machdep->machspec->kimage_voffset;
+#else
+	SNAP_info.arch_data = 0;
+#endif
 	len = dump_elf_note (ptr, NT_TASKSTRUCT, "SNAP",
 		(char *)&SNAP_info, sizeof(struct SNAP_info));
 	offset += len;

netdump.c

@@ -1172,7 +1172,14 @@ netdump_memory_dump(FILE *fp)
 	netdump_print("            nt_prpsinfo: %lx\n", nd->nt_prpsinfo);
 	netdump_print("          nt_taskstruct: %lx\n", nd->nt_taskstruct);
 	netdump_print("            task_struct: %lx\n", nd->task_struct);
-	netdump_print("               relocate: %lx\n", nd->relocate);
+	netdump_print("              arch_data: ");
+	if (nd->arch_data) {
+		if (machine_type("X86_64"))
+			netdump_print("%lx (relocate)\n", nd->arch_data);
+		else if (machine_type("ARM64"))
+			netdump_print("%lx (kimage_voffset)\n", nd->arch_data);
+	} else
+		netdump_print("(unused)\n");
 	netdump_print("           switch_stack: %lx\n", nd->switch_stack);
 	netdump_print("              page_size: %d\n", nd->page_size);
 	dump_xen_kdump_data(fp);
@@ -1770,6 +1777,24 @@ vmcoreinfo_read_string(const char *key)
 	char *vmcoreinfo = (char *)nd->vmcoreinfo;
 	char *value = NULL;
 
+	/*
+	 *  Borrow this function for ELF vmcores created by the snap.so
+	 *  extension module, where arch-specific data may be passed in 
+	 *  the NT_TASKSTRUCT note.
+	 */
+	if ((pc->flags2 & SNAP)) {
+		if (STREQ(key, "NUMBER(kimage_voffset)") && nd->arch_data) {
+			value = calloc(VADDR_PRLEN+1, sizeof(char));
+			sprintf(value, "%lx", nd->arch_data);
+			return value;
+		}
+		if (STREQ(key, "relocate") && nd->arch_data) {
+			value = calloc(VADDR_PRLEN+1, sizeof(char));
+			sprintf(value, "%lx", nd->arch_data);
+			return value;
+		}
+	}
+
 	if (!nd->vmcoreinfo)
 		return NULL;
 
@@ -2160,15 +2185,9 @@ dump_Elf64_Nhdr(Elf64_Off offset, int store)
 			nd->nt_taskstruct = (void *)note;
 			nd->task_struct = *((ulong *)(ptr + note->n_namesz));
 			if (pc->flags2 & SNAP) {
-				if (note->n_descsz == 16) {
-					nd->relocate = *((ulong *)
+				if (note->n_descsz == 16)
+					nd->arch_data = *((ulong *)
 						(ptr + note->n_namesz + sizeof(ulong)));
-					if (nd->relocate) {
-						kt->relocate = nd->relocate;
-						kt->flags |= RELOC_SET;
-						kt->flags2 |= KASLR;
-					}
-				}
 			} else if (machine_type("IA64"))
 				nd->switch_stack = *((ulong *)
 					(ptr + note->n_namesz + sizeof(ulong)));

netdump.h

@@ -77,7 +77,7 @@ struct vmcore_data {
 	ulonglong backup_src_start;
 	ulong backup_src_size;
 	ulonglong backup_offset;
-	ulong relocate;
+	ulong arch_data;
 };
 
 #define DUMP_ELF_INCOMPLETE  0x1   /* dumpfile is incomplete */

x86_64.c

@@ -184,6 +184,12 @@ x86_64_init(int when)
 		machdep->get_kvaddr_ranges = x86_64_get_kvaddr_ranges;
                 if (machdep->cmdline_args[0])
                         parse_cmdline_args();
+		if ((string = pc->read_vmcoreinfo("relocate"))) {
+			kt->relocate = htol(string, QUIET, NULL);
+                        kt->flags |= RELOC_SET;
+                        kt->flags2 |= KASLR;
+			free(string);
+		}
 		if ((string = pc->read_vmcoreinfo("NUMBER(KERNEL_IMAGE_SIZE)"))) {
 			machdep->machspec->kernel_image_size = dtol(string, QUIET, NULL);
 			free(string);