ARM: 8678/1: ftrace: Adds support for CONFIG_DYNAMIC_FTRACE_WITH_REGS

The DYNAMIC_FTRACE_WITH_REGS configuration makes it possible for a
ftrace operation to specify if registers need to saved/restored by
the ftrace handler. This is needed by kgraft and possibly other
ftrace-based tools, and the ARM architecture is currently lacking
this feature. It would also be the first step to support the
"Kprobes-on-ftrace" optimization on ARM.

This patch introduces a new ftrace handler that stores the registers
on the stack before calling the next stage. The registers are restored
from the stack before going back to the instrumented function.

A side-effect of this patch is to activate the support for
ftrace_modify_call() as it defines ARCH_SUPPORTS_FTRACE_OPS for the
ARM architecture.

Signed-off-by: Abel Vesa <abelvesa@linux.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

1 files changed, 37 insertions, 0 deletions

diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
index 833c991075a1..5617932a83df 100644
--- a/arch/arm/kernel/ftrace.c
+++ b/arch/arm/kernel/ftrace.c
@@ -141,6 +141,15 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
 
 	ret = ftrace_modify_code(pc, 0, new, false);
 
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+	if (!ret) {
+		pc = (unsigned long)&ftrace_regs_call;
+		new = ftrace_call_replace(pc, (unsigned long)func);
+
+		ret = ftrace_modify_code(pc, 0, new, false);
+	}
+#endif
+
 #ifdef CONFIG_OLD_MCOUNT
 	if (!ret) {
 		pc = (unsigned long)&ftrace_call_old;
@@ -159,11 +168,29 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 	unsigned long ip = rec->ip;
 
 	old = ftrace_nop_replace(rec);
+
+	new = ftrace_call_replace(ip, adjust_address(rec, addr));
+
+	return ftrace_modify_code(rec->ip, old, new, true);
+}
+
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+
+int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
+				unsigned long addr)
+{
+	unsigned long new, old;
+	unsigned long ip = rec->ip;
+
+	old = ftrace_call_replace(ip, adjust_address(rec, old_addr));
+
 	new = ftrace_call_replace(ip, adjust_address(rec, addr));
 
 	return ftrace_modify_code(rec->ip, old, new, true);
 }
 
+#endif
+
 int ftrace_make_nop(struct module *mod,
 		    struct dyn_ftrace *rec, unsigned long addr)
 {
@@ -231,6 +258,8 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
 extern unsigned long ftrace_graph_call;
 extern unsigned long ftrace_graph_call_old;
 extern void ftrace_graph_caller_old(void);
+extern unsigned long ftrace_graph_regs_call;
+extern void ftrace_graph_regs_caller(void);
 
 static int __ftrace_modify_caller(unsigned long *callsite,
 				  void (*func) (void), bool enable)
@@ -253,6 +282,14 @@ static int ftrace_modify_graph_caller(bool enable)
 				     ftrace_graph_caller,
 				     enable);
 
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+	if (!ret)
+		ret = __ftrace_modify_caller(&ftrace_graph_regs_call,
+				     ftrace_graph_regs_caller,
+				     enable);
+#endif
+
+
 #ifdef CONFIG_OLD_MCOUNT
 	if (!ret)
 		ret = __ftrace_modify_caller(&ftrace_graph_call_old,