[PATCH] kdump: save registers early (inline functions)
- If system panics then cpu register states are captured through funciton
crash_get_current_regs(). This is not a inline function hence a stack frame
is pushed on to the stack and then cpu register state is captured. Later
this frame is popped and new frames are pushed (machine_kexec).
- In theory this is not very right as we are capturing register states for a
frame and that frame is no more valid. This seems to have created back
trace problems for ppc64.
- This patch fixes it up. The very first thing it does after entering
crash_kexec() is to capture the register states. Anyway we don't want the
back trace beyond crash_kexec(). crash_get_current_regs() has been made
inline
- crash_setup_regs() is the top architecture dependent function which should
be responsible for capturing the register states as well as to do some
architecture dependent tricks. For ex. fixing up ss and esp for i386.
crash_setup_regs() has also been made inline to ensure no new call frame is
pushed onto stack.
Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/include/asm-i386/kexec.h b/include/asm-i386/kexec.h
index d80d446..8fb1def 100644
--- a/include/asm-i386/kexec.h
+++ b/include/asm-i386/kexec.h
@@ -2,6 +2,7 @@
#define _I386_KEXEC_H
#include <asm/fixmap.h>
+#include <asm/ptrace.h>
/*
* KEXEC_SOURCE_MEMORY_LIMIT maximum page get_free_page can return.
@@ -27,4 +28,48 @@
#define MAX_NOTE_BYTES 1024
+/* CPU does not save ss and esp on stack if execution is already
+ * running in kernel mode at the time of NMI occurrence. This code
+ * fixes it.
+ */
+static inline void crash_fixup_ss_esp(struct pt_regs *newregs,
+ struct pt_regs *oldregs)
+{
+ memcpy(newregs, oldregs, sizeof(*newregs));
+ newregs->esp = (unsigned long)&(oldregs->esp);
+ __asm__ __volatile__(
+ "xorl %%eax, %%eax\n\t"
+ "movw %%ss, %%ax\n\t"
+ :"=a"(newregs->xss));
+}
+
+/*
+ * This function is responsible for capturing register states if coming
+ * via panic otherwise just fix up the ss and esp if coming via kernel
+ * mode exception.
+ */
+static inline void crash_setup_regs(struct pt_regs *newregs,
+ struct pt_regs *oldregs)
+{
+ if (oldregs)
+ crash_fixup_ss_esp(newregs, oldregs);
+ else {
+ __asm__ __volatile__("movl %%ebx,%0" : "=m"(newregs->ebx));
+ __asm__ __volatile__("movl %%ecx,%0" : "=m"(newregs->ecx));
+ __asm__ __volatile__("movl %%edx,%0" : "=m"(newregs->edx));
+ __asm__ __volatile__("movl %%esi,%0" : "=m"(newregs->esi));
+ __asm__ __volatile__("movl %%edi,%0" : "=m"(newregs->edi));
+ __asm__ __volatile__("movl %%ebp,%0" : "=m"(newregs->ebp));
+ __asm__ __volatile__("movl %%eax,%0" : "=m"(newregs->eax));
+ __asm__ __volatile__("movl %%esp,%0" : "=m"(newregs->esp));
+ __asm__ __volatile__("movw %%ss, %%ax;" :"=a"(newregs->xss));
+ __asm__ __volatile__("movw %%cs, %%ax;" :"=a"(newregs->xcs));
+ __asm__ __volatile__("movw %%ds, %%ax;" :"=a"(newregs->xds));
+ __asm__ __volatile__("movw %%es, %%ax;" :"=a"(newregs->xes));
+ __asm__ __volatile__("pushfl; popl %0" :"=m"(newregs->eflags));
+
+ newregs->eip = (unsigned long)current_text_addr();
+ }
+}
+
#endif /* _I386_KEXEC_H */