x86: ptrace: Add function argument access API

Add regs_get_argument() which returns N th argument of the
function call.
Note that this chooses most probably assignment, in some case
it can be incorrect (e.g. passing data structure or floating
point etc.)

This is expected to be called from kprobes or ftrace with regs
where the top of stack is the return address.

Link: http://lkml.kernel.org/r/152465885737.26224.2822487520472783854.stgit@devbox

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/arch/Kconfig b/arch/Kconfig
index 6801123932a5..facace0c90fc 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -290,6 +290,13 @@ config HAVE_RSEQ
           This symbol should be selected by an architecture if it
           supports an implementation of restartable sequences.
 
+config HAVE_FUNCTION_ARG_ACCESS_API
+        bool
+        help
+          This symbol should be selected by an architecure if it supports
+          the API needed to access function arguments from pt_regs,
+          declared in asm/ptrace.h
+
 config HAVE_CLK
         bool
         help