From 471bd10f5e2880bd91a2627d887f6062494cfe9c Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Fri, 19 Aug 2016 06:53:00 -0500 Subject: [PATCH] ftrace/x86: Implement HAVE_FUNCTION_GRAPH_RET_ADDR_PTR Use the more reliable version of ftrace_graph_ret_addr() so we no longer have to worry about the unwinder getting out of sync with the function graph ret_stack index, which can happen if the unwinder skips any frames before calling ftrace_graph_ret_addr(). This fixes this issue (and several others like it): $ cat /proc/self/stack [] save_stack_trace_tsk+0x22/0x40 [] proc_pid_stack+0xb9/0x110 [] proc_single_show+0x54/0x80 [] seq_read+0x108/0x3e0 [] __vfs_read+0x37/0x140 [] vfs_read+0x99/0x140 [] SyS_read+0x58/0xc0 [] entry_SYSCALL_64_fastpath+0x1f/0xbd [] 0xffffffffffffffff $ echo function_graph > /sys/kernel/debug/tracing/current_tracer $ cat /proc/self/stack [] return_to_handler+0x0/0x27 [] print_context_stack+0xfc/0x100 [] return_to_handler+0x0/0x27 [] dump_trace+0x12b/0x350 [] return_to_handler+0x0/0x27 [] save_stack_trace_tsk+0x22/0x40 [] return_to_handler+0x0/0x27 [] proc_pid_stack+0xb9/0x110 [] return_to_handler+0x0/0x27 [] proc_single_show+0x54/0x80 [] return_to_handler+0x0/0x27 [] seq_read+0x108/0x3e0 [] return_to_handler+0x0/0x27 [] __vfs_read+0x37/0x140 [] return_to_handler+0x0/0x27 [] vfs_read+0x99/0x140 [] 0xffffffffffffffff Enabling function graph tracing causes the stack trace to change in two ways: First, the real call addresses are confusingly interspersed with 'return_to_handler' addresses. This issue will be fixed by the next patch. Second, the stack trace is offset by two frames, because the unwinder skipped the first two frames and got out of sync with the ret_stack index. This patch fixes this issue. Signed-off-by: Josh Poimboeuf Acked-by: Steven Rostedt Cc: Andy Lutomirski Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Byungchul Park Cc: Denys Vlasenko Cc: Frederic Weisbecker Cc: H. Peter Anvin Cc: Kees Cook Cc: Linus Torvalds Cc: Nilay Vaish Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/a6d623e36f8d08f9a17bd74d804d201177a23afd.1471607358.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar --- arch/x86/include/asm/ftrace.h | 2 ++ arch/x86/kernel/ftrace.c | 2 +- 2 files changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h index 37f67cbba1c6..eccd0ac6bc38 100644 --- a/arch/x86/include/asm/ftrace.h +++ b/arch/x86/include/asm/ftrace.h @@ -14,6 +14,8 @@ #define ARCH_SUPPORTS_FTRACE_OPS 1 #endif +#define HAVE_FUNCTION_GRAPH_RET_ADDR_PTR + #ifndef __ASSEMBLY__ extern void mcount(void); extern atomic_t modifying_ftrace_code; diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c index ae3b1fb2f582..8639bb2ae058 100644 --- a/arch/x86/kernel/ftrace.c +++ b/arch/x86/kernel/ftrace.c @@ -1029,7 +1029,7 @@ void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent, } if (ftrace_push_return_trace(old, self_addr, &trace.depth, - frame_pointer, NULL) == -EBUSY) { + frame_pointer, parent) == -EBUSY) { *parent = old; return; } -- 2.20.1