powerpc: Add kprobe-based event tracer

This patch ports the kprobe-based event tracer to powerpc. This patch
is based on x86 port. This brings powerpc on par with x86.

Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Acked-by: Masami Hiramatsu <mhiramat@redhat.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 64 insertions, 0 deletions

diff --git a/arch/powerpc/include/asm/ptrace.h b/arch/powerpc/include/asm/ptrace.h
index 9e2d84c06b74..5d8be0416227 100644
--- a/arch/powerpc/include/asm/ptrace.h
+++ b/arch/powerpc/include/asm/ptrace.h
@@ -89,6 +89,7 @@ struct pt_regs {
 
 #define instruction_pointer(regs) ((regs)->nip)
 #define user_stack_pointer(regs) ((regs)->gpr[1])
+#define kernel_stack_pointer(regs) ((regs)->gpr[1])
 #define regs_return_value(regs) ((regs)->gpr[3])
 
 #ifdef CONFIG_SMP
@@ -141,6 +142,69 @@ do {									      \
 #define arch_has_block_step()   (!cpu_has_feature(CPU_FTR_601))
 #define ARCH_HAS_USER_SINGLE_STEP_INFO
 
+/*
+ * kprobe-based event tracer support
+ */
+
+#include <linux/stddef.h>
+#include <linux/thread_info.h>
+extern int regs_query_register_offset(const char *name);
+extern const char *regs_query_register_name(unsigned int offset);
+#define MAX_REG_OFFSET (offsetof(struct pt_regs, dsisr))
+
+/**
+ * regs_get_register() - get register value from its offset
+ * @regs:          pt_regs from which register value is gotten
+ * @offset:    offset number of the register.
+ *
+ * regs_get_register returns the value of a register whose offset from @regs.
+ * The @offset is the offset of the register in struct pt_regs.
+ * If @offset is bigger than MAX_REG_OFFSET, this returns 0.
+ */
+static inline unsigned long regs_get_register(struct pt_regs *regs,
+                                                unsigned int offset)
+{
+        if (unlikely(offset > MAX_REG_OFFSET))
+                return 0;
+        return *(unsigned long *)((unsigned long)regs + offset);
+}
+
+/**
+ * regs_within_kernel_stack() - check the address in the stack
+ * @regs:      pt_regs which contains kernel stack pointer.
+ * @addr:      address which is checked.
+ *
+ * regs_within_kernel_stack() checks @addr is within the kernel stack page(s).
+ * If @addr is within the kernel stack, it returns true. If not, returns false.
+ */
+
+static inline bool regs_within_kernel_stack(struct pt_regs *regs,
+                                                unsigned long addr)
+{
+        return ((addr & ~(THREAD_SIZE - 1))  ==
+                (kernel_stack_pointer(regs) & ~(THREAD_SIZE - 1)));
+}
+
+/**
+ * regs_get_kernel_stack_nth() - get Nth entry of the stack
+ * @regs:       pt_regs which contains kernel stack pointer.
+ * @n:          stack entry number.
+ *
+ * regs_get_kernel_stack_nth() returns @n th entry of the kernel stack which
+ * is specified by @regs. If the @n th entry is NOT in the kernel stack,
+ * this returns 0.
+ */
+static inline unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs,
+                                                      unsigned int n)
+{
+        unsigned long *addr = (unsigned long *)kernel_stack_pointer(regs);
+        addr += n;
+        if (regs_within_kernel_stack(regs, (unsigned long)addr))
+                return *addr;
+        else
+                return 0;
+}
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __KERNEL__ */