Commit 45f7a0da authored Dec 10, 2019 by Vasily Gorbik

s390/ftrace: generate traced function stack frame



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>

parent 253b3c4b

arch/s390/kernel/mcount.S

+14 −1

Original line number	Diff line number	Diff line
		@@ -26,6 +26,12 @@ ENDPROC(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
		@@ -39,9 +45,16 @@ ENTRY(ftrace_caller)
		#if !(defined(CC_USING_HOTPATCH) \|\| defined(CC_USING_NOP_MCOUNT))
		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

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