[PATCH] kexec: x86: snapshot registers during crash shutdown

After the kernel panics if we wish to generate an entire machine core file it
is very nice to know the register state at the time the machine crashed.

After long discussion it was realized that if you are going to be saving the
information anyway it is reasonable to store the information in a format that
it will be used and recognized in so the register state is stored in the
standard ELF note format.
Signed-off-by: Eric Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/i386/kernel/crash.c

@@ -30,12 +30,91 @@ typedef u32 note_buf_t[MAX_NOTE_BYTES/4];
 
 note_buf_t crash_notes[NR_CPUS];
 
+static u32 *append_elf_note(u32 *buf,
+	char *name, unsigned type, void *data, size_t data_len)
+{
+	struct elf_note note;
+	note.n_namesz = strlen(name) + 1;
+	note.n_descsz = data_len;
+	note.n_type   = type;
+	memcpy(buf, &note, sizeof(note));
+	buf += (sizeof(note) +3)/4;
+	memcpy(buf, name, note.n_namesz);
+	buf += (note.n_namesz + 3)/4;
+	memcpy(buf, data, note.n_descsz);
+	buf += (note.n_descsz + 3)/4;
+	return buf;
+}
+
+static void final_note(u32 *buf)
+{
+	struct elf_note note;
+	note.n_namesz = 0;
+	note.n_descsz = 0;
+	note.n_type   = 0;
+	memcpy(buf, &note, sizeof(note));
+}
+
+
+static void crash_save_this_cpu(struct pt_regs *regs, int cpu)
+{
+	struct elf_prstatus prstatus;
+	u32 *buf;
+	if ((cpu < 0) || (cpu >= NR_CPUS)) {
+		return;
+	}
+	/* Using ELF notes here is opportunistic.
+	 * I need a well defined structure format
+	 * for the data I pass, and I need tags
+	 * on the data to indicate what information I have
+	 * squirrelled away.  ELF notes happen to provide
+	 * all of that that no need to invent something new.
+	 */
+	buf = &crash_notes[cpu][0];
+	memset(&prstatus, 0, sizeof(prstatus));
+	prstatus.pr_pid = current->pid;
+	elf_core_copy_regs(&prstatus.pr_reg, regs);
+	buf = append_elf_note(buf, "CORE", NT_PRSTATUS,
+		&prstatus, sizeof(prstatus));
+
+	final_note(buf);
+}
+
+static void crash_get_current_regs(struct pt_regs *regs)
+{
+	__asm__ __volatile__("movl %%ebx,%0" : "=m"(regs->ebx));
+	__asm__ __volatile__("movl %%ecx,%0" : "=m"(regs->ecx));
+	__asm__ __volatile__("movl %%edx,%0" : "=m"(regs->edx));
+	__asm__ __volatile__("movl %%esi,%0" : "=m"(regs->esi));
+	__asm__ __volatile__("movl %%edi,%0" : "=m"(regs->edi));
+	__asm__ __volatile__("movl %%ebp,%0" : "=m"(regs->ebp));
+	__asm__ __volatile__("movl %%eax,%0" : "=m"(regs->eax));
+	__asm__ __volatile__("movl %%esp,%0" : "=m"(regs->esp));
+	__asm__ __volatile__("movw %%ss, %%ax;" :"=a"(regs->xss));
+	__asm__ __volatile__("movw %%cs, %%ax;" :"=a"(regs->xcs));
+	__asm__ __volatile__("movw %%ds, %%ax;" :"=a"(regs->xds));
+	__asm__ __volatile__("movw %%es, %%ax;" :"=a"(regs->xes));
+	__asm__ __volatile__("pushfl; popl %0" :"=m"(regs->eflags));
+
+	regs->eip = (unsigned long)current_text_addr();
+}
+
+static void crash_save_self(void)
+{
+	struct pt_regs regs;
+	int cpu;
+	cpu = smp_processor_id();
+	crash_get_current_regs(&regs);
+	crash_save_this_cpu(&regs, cpu);
+}
+
 #ifdef CONFIG_SMP
 static atomic_t waiting_for_crash_ipi;
 
 static int crash_nmi_callback(struct pt_regs *regs, int cpu)
 {
 	local_irq_disable();
+	crash_save_this_cpu(regs, cpu);
 	atomic_dec(&waiting_for_crash_ipi);
 	/* Assume hlt works */
 	__asm__("hlt");
@@ -95,4 +174,5 @@ void machine_crash_shutdown(void)
 	/* The kernel is broken so disable interrupts */
 	local_irq_disable();
 	nmi_shootdown_cpus();
+	crash_save_self();
 }