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    Subject[PATCH AUTOSEL 5.5 434/542] 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 c3597d2e2ae0e..f942341429b1c 100644
    --- a/arch/s390/kernel/mcount.S
    +++ b/arch/s390/kernel/mcount.S
    @@ -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
    @@ -40,9 +46,16 @@ 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
    --
    2.20.1
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