[Crash-utility] [PATCH] ARM: corrupted pages tables vs unwind

[Rabin Vincent]

I have access to a system whose crashdump extraction mechanism
unfortunately trashes the first few hundred kilobytes of physical
memory,  which includes the page tables at swapper_pg_dir.

crash does chug along and remains quite useful without these page tables
since much of the interesting information is in the direct mapped
region, but it disables the use of the unwind tables because it
fails to read the module unwind tables, which are placed at a
non-direct-mapped address.

The patch below allows unwind tables to be used only for core kernel
addresses if the module tables are inaccessible.

Alternatively, we could perhaps not attempt to read the
module unwind tables when --no_modules is specified.

Rabin

diff --git a/unwind_arm.c b/unwind_arm.c
index 6554804..a21c592 100644
--- a/unwind_arm.c
+++ b/unwind_arm.c
@@ -148,8 +148,6 @@ init_unwind_tables(void)
 	if (!init_module_unwind_tables()) {
 		error(WARNING,
 		      "UNWIND: failed to initialize module unwind tables\n");
-		free_kernel_unwind_table();
-		return FALSE;
 	}
 
 	/*
@@ -347,6 +345,7 @@ fail:
 	}
 
 	free(module_unwind_tables);
+	module_unwind_tables = NULL;
 	return FALSE;
 }
 
@@ -536,7 +535,7 @@ search_table(ulong ip)
 	 */
 	if (is_core_kernel_text(ip)) {
 		return kernel_unwind_table;
-	} else {
+	} else if (module_unwind_tables) {
 		struct unwind_table *tbl;
 
 		for (tbl = &module_unwind_tables[0]; tbl->idx; tbl++) {