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Subject[PATCH AUTOSEL 4.9 111/141] s390/ftrace: generate traced function stack frame
Date
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 be75e8e49e43d..802a4ded9a626 100644
--- a/arch/s390/kernel/mcount.S
+++ b/arch/s390/kernel/mcount.S
@@ -24,6 +24,12 @@ 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
@@ -37,9 +43,16 @@ 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
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