[Crash-utility] [PATCH] Improve error handling when architecture doesn't match

[Bernhard Walle]

Currently, crash prints always

        crash: vmcore: not a supported file format

if you try to open a dump file which is not supported. However, it can be
misleading if you have a valid ELF core dump, but just use crash for the wrong
architecture. In the case I observed the user had a ELF64 x86 dump file and
assumed it's x86-64. However, it just was a i386 core dump which was ELF64
because kexec was called with --elf64-core-headers which makes sense
if the i386 machine has PAE and possibly more than 4 GiB of physical RAM.

After that patch is applied, an example output is

        Looks like a valid ELF dump, but host architecture (X86_64) \
        doesn't match dump architecture (IA64).

or if I try to open a PPC64 dump on x86-64:

        Looks like a valid ELF dump, but host endianess (LE) \
        doesn't match target endianess (BE)

Please review and consider applying.


Signed-off-by: Bernhard Walle <bwalle at suse.de>

---
 defs.h    |    3 ++-
 netdump.c |   48 +++++++++++++++++++++++++++++++++++++++++++-----
 tools.c   |    9 ++++++++-
 3 files changed, 53 insertions(+), 7 deletions(-)

--- a/defs.h
+++ b/defs.h
@@ -3198,7 +3198,8 @@ void stall(ulong);
 char *pages_to_size(ulong, char *);
 int clean_arg(void);
 int empty_list(ulong);
-int machine_type(char *);
+int machine_type(const char *);
+int is_big_endian(void);
 void command_not_supported(void);
 void option_not_supported(int);
 void please_wait(char *);
--- a/netdump.c
+++ b/netdump.c
@@ -36,6 +36,32 @@ static void check_dumpfile_size(char *);
 #define ELFREAD  0
 
 #define MIN_PAGE_SIZE (4096)
+
+
+/*
+ * Checks if the machine type of the host matches required_type.
+ * If not, it prints a short error message for the user.
+ */
+static int machine_type_error(const char *required_type)
+{
+	if (machine_type(required_type))
+		return 1;
+	else {
+		fprintf(stderr, "Looks like a valid ELF dump, but host "
+				"architecture (%s) doesn't match dump "
+				"architecture (%s).\n",
+				MACHINE_TYPE, required_type);
+		return 0;
+	}
+}
+
+/*
+ * Returns endianess in a string
+ */
+static const char *endianess_to_string(int big_endian)
+{
+	return big_endian ? "BE" : "LE";
+}
 	
 /*
  *  Determine whether a file is a netdump/diskdump/kdump creation, 
@@ -98,6 +124,18 @@ is_netdump(char *file, ulong source_quer
 	 *  If either kdump difference is seen, presume kdump -- this
 	 *  is obviously subject to change.
 	 */
+
+	/* check endianess */
+	if ((STRNEQ(elf32->e_ident, ELFMAG) || STRNEQ(elf64->e_ident, ELFMAG)) &&
+			(elf32->e_type == ET_CORE || elf64->e_type == ET_CORE) &&
+			(elf32->e_ident[EI_DATA] == ELFDATA2LSB && is_big_endian()) ||
+			(elf32->e_ident[EI_DATA] == ELFDATA2MSB && !is_big_endian()))
+		fprintf(stderr, "Looks like a valid ELF dump, but host "
+				"endianess (%s) doesn't match target "
+				"endianess (%s)\n",
+			endianess_to_string(is_big_endian()),
+			endianess_to_string(elf32->e_ident[EI_DATA] == ELFDATA2MSB));
+
         if (STRNEQ(elf32->e_ident, ELFMAG) && 
 	    (elf32->e_ident[EI_CLASS] == ELFCLASS32) &&
   	    (elf32->e_ident[EI_DATA] == ELFDATA2LSB) &&
@@ -108,7 +146,7 @@ is_netdump(char *file, ulong source_quer
 		switch (elf32->e_machine)
 		{
 		case EM_386:
-			if (machine_type("X86"))
+			if (machine_type_error("X86"))
 				break;
 		default:
                 	goto bailout;
@@ -133,28 +171,28 @@ is_netdump(char *file, ulong source_quer
 		{
 		case EM_IA_64:
 			if ((elf64->e_ident[EI_DATA] == ELFDATA2LSB) &&
-				machine_type("IA64"))
+				machine_type_error("IA64"))
 				break;
 			else
 				goto bailout;
 
 		case EM_PPC64:
 			if ((elf64->e_ident[EI_DATA] == ELFDATA2MSB) &&
-				machine_type("PPC64"))
+				machine_type_error("PPC64"))
 				break;
 			else
 				goto bailout;
 
 		case EM_X86_64:
 			if ((elf64->e_ident[EI_DATA] == ELFDATA2LSB) &&
-				machine_type("X86_64"))
+				machine_type_error("X86_64"))
 				break;
 			else
 				goto bailout;
 
 		case EM_386:
 			if ((elf64->e_ident[EI_DATA] == ELFDATA2LSB) &&
-				machine_type("X86"))
+				machine_type_error("X86"))
 				break;
 			else
 				goto bailout;
--- a/tools.c
+++ b/tools.c
@@ -4518,11 +4518,18 @@ empty_list(ulong list_head_addr)
 }
 
 int
-machine_type(char *type)
+machine_type(const char *type)
 {
 	return STREQ(MACHINE_TYPE, type);
 }
 
+int
+is_big_endian(void)
+{
+	unsigned short value = 0xff;
+	return *((unsigned char *)&value) != 0xff;
+}
+
 void
 command_not_supported()
 {