[ARM] 5387/1: Add ptrace VFP support on ARM

This patch adds ptrace support for setting and getting the VFP registers
using PTRACE_SETVFPREGS and PTRACE_GETVFPREGS. The user_vfp structure
defined in asm/user.h contains 32 double registers (to cover VFPv3 and
Neon hardware) and the FPSCR register.

Cc: Paul Brook <[e-mail]>
Cc: Daniel Jacobowitz <[e-mail]>
Signed-off-by: Catalin Marinas <[e-mail]>
Signed-off-by: Russell King <[e-mail]>

arch/arm/include/asm/ptrace.h

···
 /* PTRACE_SYSCALL is 24 */
 #define PTRACE_GETCRUNCHREGS	25
 #define PTRACE_SETCRUNCHREGS	26
+#define PTRACE_GETVFPREGS	27
+#define PTRACE_SETVFPREGS	28
 
 /*
  * PSR bits

arch/arm/include/asm/thread_info.h

···
 extern void iwmmxt_task_release(struct thread_info *);
 extern void iwmmxt_task_switch(struct thread_info *);
 
+extern void vfp_sync_state(struct thread_info *thread);
+
 #endif
 
 /*

arch/arm/include/asm/user.h

···
 #define HOST_TEXT_START_ADDR (u.start_code)
 #define HOST_STACK_END_ADDR (u.start_stack + u.u_ssize * NBPG)
 
+/*
+ * User specific VFP registers. If only VFPv2 is present, registers 16 to 31
+ * are ignored by the ptrace system call.
+ */
+struct user_vfp {
+	unsigned long long fpregs[32];
+	unsigned long fpscr;
+};
+
 #endif /* _ARM_USER_H */

arch/arm/kernel/ptrace.c

···
 }
 #endif
 
+#ifdef CONFIG_VFP
+/*
+ * Get the child VFP state.
+ */
+static int ptrace_getvfpregs(struct task_struct *tsk, void __user *data)
+{
+	struct thread_info *thread = task_thread_info(tsk);
+	union vfp_state *vfp = &thread->vfpstate;
+	struct user_vfp __user *ufp = data;
+
+	vfp_sync_state(thread);
+
+	/* copy the floating point registers */
+	if (copy_to_user(&ufp->fpregs, &vfp->hard.fpregs,
+			 sizeof(vfp->hard.fpregs)))
+		return -EFAULT;
+
+	/* copy the status and control register */
+	if (put_user(vfp->hard.fpscr, &ufp->fpscr))
+		return -EFAULT;
+
+	return 0;
+}
+
+/*
+ * Set the child VFP state.
+ */
+static int ptrace_setvfpregs(struct task_struct *tsk, void __user *data)
+{
+	struct thread_info *thread = task_thread_info(tsk);
+	union vfp_state *vfp = &thread->vfpstate;
+	struct user_vfp __user *ufp = data;
+
+	vfp_sync_state(thread);
+
+	/* copy the floating point registers */
+	if (copy_from_user(&vfp->hard.fpregs, &ufp->fpregs,
+			   sizeof(vfp->hard.fpregs)))
+		return -EFAULT;
+
+	/* copy the status and control register */
+	if (get_user(vfp->hard.fpscr, &ufp->fpscr))
+		return -EFAULT;
+
+	return 0;
+}
+#endif
+
 long arch_ptrace(struct task_struct *child, long request, long addr, long data)
 {
 	int ret;
···
 
 		case PTRACE_SETCRUNCHREGS:
 			ret = ptrace_setcrunchregs(child, (void __user *)data);
+			break;
+#endif
+
+#ifdef CONFIG_VFP
+		case PTRACE_GETVFPREGS:
+			ret = ptrace_getvfpregs(child, (void __user *)data);
+			break;
+
+		case PTRACE_SETVFPREGS:
+			ret = ptrace_setvfpregs(child, (void __user *)data);
 			break;
 #endif
 

arch/arm/vfp/vfp.h

···
 	u32 flags;
 };
 
-#if defined(CONFIG_SMP) || defined(CONFIG_PM)
 extern void vfp_save_state(void *location, u32 fpexc);
-#endif

arch/arm/vfp/vfphw.S

···
 					@ retry the faulted instruction
 ENDPROC(vfp_support_entry)
 
-#if defined(CONFIG_SMP) || defined(CONFIG_PM)
 ENTRY(vfp_save_state)
 	@ Save the current VFP state
 	@ r0 - save location
···
 	stmia	r0, {r1, r2, r3, r12}	@ save FPEXC, FPSCR, FPINST, FPINST2
 	mov	pc, lr
 ENDPROC(vfp_save_state)
-#endif
 
 last_VFP_context_address:
 	.word	last_VFP_context

arch/arm/vfp/vfpmodule.c

···
 static inline void vfp_pm_init(void) { }
 #endif /* CONFIG_PM */
 
+/*
+ * Synchronise the hardware VFP state of a thread other than current with the
+ * saved one. This function is used by the ptrace mechanism.
+ */
+#ifdef CONFIG_SMP
+void vfp_sync_state(struct thread_info *thread)
+{
+	/*
+	 * On SMP systems, the VFP state is automatically saved at every
+	 * context switch. We mark the thread VFP state as belonging to a
+	 * non-existent CPU so that the saved one will be reloaded when
+	 * needed.
+	 */
+	thread->vfpstate.hard.cpu = NR_CPUS;
+}
+#else
+void vfp_sync_state(struct thread_info *thread)
+{
+	unsigned int cpu = get_cpu();
+	u32 fpexc = fmrx(FPEXC);
+
+	/*
+	 * If VFP is enabled, the previous state was already saved and
+	 * last_VFP_context updated.
+	 */
+	if (fpexc & FPEXC_EN)
+		goto out;
+
+	if (!last_VFP_context[cpu])
+		goto out;
+
+	/*
+	 * Save the last VFP state on this CPU.
+	 */
+	fmxr(FPEXC, fpexc | FPEXC_EN);
+	vfp_save_state(last_VFP_context[cpu], fpexc);
+	fmxr(FPEXC, fpexc);
+
+	/*
+	 * Set the context to NULL to force a reload the next time the thread
+	 * uses the VFP.
+	 */
+	last_VFP_context[cpu] = NULL;
+
+out:
+	put_cpu();
+}
+#endif
+
 #include <linux/smp.h>
 
 /*