[Crash-utility] [patch] Crash-Utility: ppc64: Fix a crash issue where it fails to read vmcore generated by post-v2.6.34 kernel version.

[Mahesh J Salgaonkar]

With some changes in the upstream ppc64 kernel starting from 2.6.34, the
crash utility fails to read vmcore generated by post-v2.6.34 kernel versions.

In v2.6.34 ppc64, the upstream commit 1426d5a3bd07589534286375998c0c8c6fdc5260
(powerpc: Dynamically allocate pacas) now dynamically allocates the paca and
have changed data type of 'paca' symbol from array to pointer. With this change
in place crash utility fails to read vmcore generated for upstream kernel.

This patch fixes the crash tool to get correct address value for paca
symbol depending on its data type.

In v2.6.36 ppc64, the upstream commit fc53b4202e61c7e9008c241933ae282aab8a6082
overwrites the paca pointer variable to point to static paca (during crash
just before kexec) that contains valid data_offset only for crashing cpu.
Hence we can not rely on paca symbol anymore to get valid per cpu data_offset
values. Instead, this version introduces __per_cpu_offset array again which
was removed post v2.6.15 ppc64. This patch checks for existence of
'__per_cpu_offset' symbol before calling ppc64_paca_init().

This fix is backward compatible and works fine with vmcore generated by older
kernel (pre-2.6.34).


Signed-off-by: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
---
 ppc64.c |   34 ++++++++++++++++++++++++++++++++--
 1 file changed, 32 insertions(+), 2 deletions(-)

Index: crash-5.1.7/ppc64.c
===================================================================
--- crash-5.1.7.orig/ppc64.c
+++ crash-5.1.7/ppc64.c
@@ -201,7 +201,22 @@ ppc64_init(int when)
 
 		machdep->section_size_bits = _SECTION_SIZE_BITS;
 		machdep->max_physmem_bits = _MAX_PHYSMEM_BITS;
-		ppc64_paca_init();
+		/*
+		 * starting from v2.6.36 we can not rely on paca structure
+		 * to get per cpu data_offset. The upstream commit
+		 * fc53b4202e61c7e9008c241933ae282aab8a6082 overwrites the
+		 * paca pointer variable to point to static paca that contains
+		 * valid data_offset only for crashing cpu.
+		 *
+		 * But the kernel v2.6.36 ppc64 introduces __per_cpu_offset
+		 * symbol which was removed post v2.6.15 ppc64 and now we
+		 * get the per cpu data_offset from __per_cpu_offset symbol
+		 * during kernel_init() call. Hence for backward (pre-2.6.36)
+		 * compatibility, call ppc64_paca_init() only if symbol
+		 * __per_cpu_offset does not exist.
+		 */
+		if (!symbol_exists("__per_cpu_offset"))
+			ppc64_paca_init();
 		machdep->vmalloc_start = ppc64_vmalloc_start;
 		MEMBER_OFFSET_INIT(thread_struct_pg_tables,
 			"thread_struct", "pg_tables");
@@ -2606,10 +2621,25 @@ ppc64_paca_init(void)
 	char *cpu_paca_buf;
 	ulong data_offset;
 	int map;
+	ulong paca;
 
 	if (!symbol_exists("paca"))
 		error(FATAL, "PPC64: Could not find 'paca' symbol\n");
+	/*
+	 * In v2.6.34 ppc64, the upstream commit
+	 * 1426d5a3bd07589534286375998c0c8c6fdc5260 (powerpc: Dynamically
+	 * allocate pacas) now dynamically allocates the paca and have
+	 * changed data type of 'paca' symbol from array to pointer. With this
+	 * change in place crash utility fails to read vmcore generated for
+	 * upstream kernel.
+	 * Add a check for paca variable data type before accessing.
+	 */
 
+	if (get_symbol_type("paca", NULL, NULL) == TYPE_CODE_PTR)
+		readmem(symbol_value("paca"), KVADDR, &paca, sizeof(ulong),
+				"paca", FAULT_ON_ERROR);
+	else
+		paca = symbol_value("paca");
 	if (cpu_map_addr("possible"))
 		map = POSSIBLE;
 	else if (cpu_map_addr("present"))
@@ -2648,7 +2678,7 @@ ppc64_paca_init(void)
 		if (!in_cpu_map(map, i))
 			continue;
 
-        	readmem(symbol_value("paca") + (i * SIZE(ppc64_paca)),
+		readmem(paca + (i * SIZE(ppc64_paca)),
              		KVADDR, cpu_paca_buf, SIZE(ppc64_paca),
 			"paca entry", FAULT_ON_ERROR);