[RFC PATCH v2 tip 4/7] Revert "x86/ptrace: Remove unused regs_get_argument_nth API"

[Alexei Starovoitov <ast@plumgrid.com>]

This reverts commit aa5add93e92019018e905146f8c3d3f8e3c08300.

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
---
 arch/x86/include/asm/ptrace.h |    3 +++
 arch/x86/kernel/ptrace.c      |   24 ++++++++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
index 14fd6fd..e026176 100644
--- a/arch/x86/include/asm/ptrace.h
+++ b/arch/x86/include/asm/ptrace.h
@@ -222,6 +222,9 @@ static inline unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs,
 		return 0;
 }
 
+/* Get Nth argument at function call */
+unsigned long regs_get_argument_nth(struct pt_regs *regs, unsigned int n);
+
 #define arch_has_single_step()	(1)
 #ifdef CONFIG_X86_DEBUGCTLMSR
 #define arch_has_block_step()	(1)
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 7461f50..ac1c705 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -141,6 +141,30 @@ static const int arg_offs_table[] = {
 #endif
 };
 
+/**
+ * regs_get_argument_nth() - get Nth argument at function call
+ * @regs:	pt_regs which contains registers at function entry.
+ * @n:		argument number.
+ *
+ * regs_get_argument_nth() returns @n th argument of a function call.
+ * Since usually the kernel stack will be changed right after function entry,
+ * you must use this at function entry. If the @n th entry is NOT in the
+ * kernel stack or pt_regs, this returns 0.
+ */
+unsigned long regs_get_argument_nth(struct pt_regs *regs, unsigned int n)
+{
+	if (n < ARRAY_SIZE(arg_offs_table))
+		return *(unsigned long *)((char *)regs + arg_offs_table[n]);
+	else {
+		/*
+		 * The typical case: arg n is on the stack.
+		 * (Note: stack[0] = return address, so skip it)
+		 */
+		n -= ARRAY_SIZE(arg_offs_table);
+		return regs_get_kernel_stack_nth(regs, 1 + n);
+	}
+}
+
 /*
  * does not yet catch signals sent when the child dies.
  * in exit.c or in signal.c.
-- 
1.7.9.5