ftrace/x86: Add separate function to save regs

Add a way to have different functions calling different trampolines.
If a ftrace_ops wants regs saved on the return, then have only the
functions with ops registered to save regs. Functions registered by
other ops would not be affected, unless the functions overlap.

If one ftrace_ops registered functions A, B and C and another ops
registered fucntions to save regs on A, and D, then only functions
A and D would be saving regs. Function B and C would work as normal.
Although A is registered by both ops: normal and saves regs; this is fine
as saving the regs is needed to satisfy one of the ops that calls it
but the regs are ignored by the other ops function.

x86_64 implements the full regs saving, and i386 just passes a NULL
for regs to satisfy the ftrace_ops passing. Where an arch must supply
both regs and ftrace_ops parameters, even if regs is just NULL.

It is OK for an arch to pass NULL regs. All function trace users that
require regs passing must add the flag FTRACE_OPS_FL_SAVE_REGS when
registering the ftrace_ops. If the arch does not support saving regs
then the ftrace_ops will fail to register. The flag
FTRACE_OPS_FL_SAVE_REGS_IF_SUPPORTED may be set that will prevent the
ftrace_ops from failing to register. In this case, the handler may
either check if regs is not NULL or check if ARCH_SUPPORTS_FTRACE_SAVE_REGS.
If the arch supports passing regs it will set this macro and pass regs
for ops that request them. All other archs will just pass NULL.

Link: Link: http://lkml.kernel.org/r/20120711195745.107705970@goodmis.org

Cc: Alexander van Heukelum <heukelum@fastmail.fm>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 28 insertions, 19 deletions

diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
index b3bb1f3f2773..a8475014c4ad 100644
--- a/arch/x86/include/asm/ftrace.h
+++ b/arch/x86/include/asm/ftrace.h
@@ -3,27 +3,33 @@
 
 #ifdef __ASSEMBLY__
 
-        .macro MCOUNT_SAVE_FRAME
-        /* taken from glibc */
-        subq $0x38, %rsp
-        movq %rax, (%rsp)
-        movq %rcx, 8(%rsp)
-        movq %rdx, 16(%rsp)
-        movq %rsi, 24(%rsp)
-        movq %rdi, 32(%rsp)
-        movq %r8, 40(%rsp)
-        movq %r9, 48(%rsp)
+        /* skip is set if the stack was already partially adjusted */
+        .macro MCOUNT_SAVE_FRAME skip=0
+         /*
+          * We add enough stack to save all regs.
+          */
+        subq $(SS+8-\skip), %rsp
+        movq %rax, RAX(%rsp)
+        movq %rcx, RCX(%rsp)
+        movq %rdx, RDX(%rsp)
+        movq %rsi, RSI(%rsp)
+        movq %rdi, RDI(%rsp)
+        movq %r8, R8(%rsp)
+        movq %r9, R9(%rsp)
+         /* Move RIP to its proper location */
+        movq SS+8(%rsp), %rdx
+        movq %rdx, RIP(%rsp)
         .endm
 
-        .macro MCOUNT_RESTORE_FRAME
-        movq 48(%rsp), %r9
-        movq 40(%rsp), %r8
-        movq 32(%rsp), %rdi
-        movq 24(%rsp), %rsi
-        movq 16(%rsp), %rdx
-        movq 8(%rsp), %rcx
-        movq (%rsp), %rax
-        addq $0x38, %rsp
+        .macro MCOUNT_RESTORE_FRAME skip=0
+        movq R9(%rsp), %r9
+        movq R8(%rsp), %r8
+        movq RDI(%rsp), %rdi
+        movq RSI(%rsp), %rsi
+        movq RDX(%rsp), %rdx
+        movq RCX(%rsp), %rcx
+        movq RAX(%rsp), %rax
+        addq $(SS+8-\skip), %rsp
         .endm
 
 #endif
@@ -34,6 +40,9 @@
 
 #ifdef CONFIG_DYNAMIC_FTRACE
 #define ARCH_SUPPORTS_FTRACE_OPS 1
+#ifdef CONFIG_X86_64
+#define ARCH_SUPPORTS_FTRACE_SAVE_REGS
+#endif
 #endif
 
 #ifndef __ASSEMBLY__