[PATCH AUTOSEL 4.4 078/100] s390/ftrace: generate traced function stack frame

[Sasha Levin <sashal@kernel.org>]

From: Vasily Gorbik <gor@linux.ibm.com>

[ Upstream commit 45f7a0da600d3c409b5ad8d5ddddacd98ddc8840 ]

Currently backtrace from ftraced function does not contain ftraced
function itself. e.g. for "path_openat":

arch_stack_walk+0x15c/0x2d8
stack_trace_save+0x50/0x68
stack_trace_call+0x15e/0x3d8
ftrace_graph_caller+0x0/0x1c <-- ftrace code
do_filp_open+0x7c/0xe8 <-- ftraced function caller
do_open_execat+0x76/0x1b8
open_exec+0x52/0x78
load_elf_binary+0x180/0x1160
search_binary_handler+0x8e/0x288
load_script+0x2a8/0x2b8
search_binary_handler+0x8e/0x288
__do_execve_file.isra.39+0x6fa/0xb40
__s390x_sys_execve+0x56/0x68
system_call+0xdc/0x2d8

Ftraced function is expected in the backtrace by ftrace kselftests, which
are now failing. It would also be nice to have it for clarity reasons.

"ftrace_caller" itself is called without stack frame allocated for it
and does not store its caller (ftraced function). Instead it simply
allocates a stack frame for "ftrace_trace_function" and sets backchain
to point to ftraced function stack frame (which contains ftraced function
caller in saved r14).

To fix this issue make "ftrace_caller" allocate a stack frame
for itself just to store ftraced function for the stack unwinder.
As a result backtrace looks like the following:

arch_stack_walk+0x15c/0x2d8
stack_trace_save+0x50/0x68
stack_trace_call+0x15e/0x3d8
ftrace_graph_caller+0x0/0x1c <-- ftrace code
path_openat+0x6/0xd60  <-- ftraced function
do_filp_open+0x7c/0xe8 <-- ftraced function caller
do_open_execat+0x76/0x1b8
open_exec+0x52/0x78
load_elf_binary+0x180/0x1160
search_binary_handler+0x8e/0x288
load_script+0x2a8/0x2b8
search_binary_handler+0x8e/0x288
__do_execve_file.isra.39+0x6fa/0xb40
__s390x_sys_execve+0x56/0x68
system_call+0xdc/0x2d8

Reported-by: Sven Schnelle <sven.schnelle@ibm.com>
Tested-by: Sven Schnelle <sven.schnelle@ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/s390/kernel/mcount.S | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/s390/kernel/mcount.S b/arch/s390/kernel/mcount.S
index 6c1c7d399bf95..78ba14546e007 100644
--- a/arch/s390/kernel/mcount.S
+++ b/arch/s390/kernel/mcount.S
@@ -23,6 +23,12 @@ ENTRY(ftrace_stub)
 #define STACK_PTREGS	  (STACK_FRAME_OVERHEAD)
 #define STACK_PTREGS_GPRS (STACK_PTREGS + __PT_GPRS)
 #define STACK_PTREGS_PSW  (STACK_PTREGS + __PT_PSW)
+#ifdef __PACK_STACK
+/* allocate just enough for r14, r15 and backchain */
+#define TRACED_FUNC_FRAME_SIZE	24
+#else
+#define TRACED_FUNC_FRAME_SIZE	STACK_FRAME_OVERHEAD
+#endif
 
 ENTRY(_mcount)
 	BR_EX	%r14
@@ -34,9 +40,16 @@ ENTRY(ftrace_caller)
 #ifndef CC_USING_HOTPATCH
 	aghi	%r0,MCOUNT_RETURN_FIXUP
 #endif
-	aghi	%r15,-STACK_FRAME_SIZE
+	# allocate stack frame for ftrace_caller to contain traced function
+	aghi	%r15,-TRACED_FUNC_FRAME_SIZE
 	stg	%r1,__SF_BACKCHAIN(%r15)
+	stg	%r0,(__SF_GPRS+8*8)(%r15)
+	stg	%r15,(__SF_GPRS+9*8)(%r15)
+	# allocate pt_regs and stack frame for ftrace_trace_function
+	aghi	%r15,-STACK_FRAME_SIZE
 	stg	%r1,(STACK_PTREGS_GPRS+15*8)(%r15)
+	aghi	%r1,-TRACED_FUNC_FRAME_SIZE
+	stg	%r1,__SF_BACKCHAIN(%r15)
 	stg	%r0,(STACK_PTREGS_PSW+8)(%r15)
 	stmg	%r2,%r14,(STACK_PTREGS_GPRS+2*8)(%r15)
 #ifdef CONFIG_HAVE_MARCH_Z196_FEATURES
-- 
2.20.1