x86/ftrace: Add -mfentry support to x86_32 with DYNAMIC_FTRACE set

x86_64 has had fentry support for some time. I did not add support to x86_32
as I was unsure if it will be used much in the future. It is still very much
used, and there's issues with function graph tracing with gcc playing around
with the mcount frames, causing function graph to panic. The fentry code
does not have this issue, and is able to cope as there is no frame to mess
up.

Note, this only adds support for fentry when DYNAMIC_FTRACE is set. There's
really no reason to not have that set, because the performance of the
machine drops significantly when it's not enabled.

Keep !DYNAMIC_FTRACE around to test it off, as there's still some archs
that have FTRACE but not DYNAMIC_FTRACE.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20170323143446.052202377@goodmis.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

2 files changed, 73 insertions, 11 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index cc98d5a294ee..8c17146427ca 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -127,7 +127,7 @@ config X86
         select HAVE_EBPF_JIT                    if X86_64
         select HAVE_EFFICIENT_UNALIGNED_ACCESS
         select HAVE_EXIT_THREAD
-        select HAVE_FENTRY                      if X86_64
+        select HAVE_FENTRY                      if X86_64 || DYNAMIC_FTRACE
         select HAVE_FTRACE_MCOUNT_RECORD
         select HAVE_FUNCTION_GRAPH_TRACER
         select HAVE_FUNCTION_TRACER
diff --git a/arch/x86/kernel/ftrace_32.S b/arch/x86/kernel/ftrace_32.S
index 93e26647c3f2..80518ec5b882 100644
--- a/arch/x86/kernel/ftrace_32.S
+++ b/arch/x86/kernel/ftrace_32.S
@@ -9,26 +9,68 @@
 #include <asm/ftrace.h>
 
 #ifdef CONFIG_FUNCTION_TRACER
+
+#ifdef CC_USING_FENTRY
+# define function_hook  __fentry__
+EXPORT_SYMBOL(__fentry__)
+#else
+# define function_hook  mcount
+EXPORT_SYMBOL(mcount)
+#endif
+
 #ifdef CONFIG_DYNAMIC_FTRACE
 
-ENTRY(mcount)
+/* mcount uses a frame pointer even if CONFIG_FRAME_POINTER is not set */
+#if !defined(CC_USING_FENTRY) || defined(CONFIG_FRAME_POINTER)
+# define USING_FRAME_POINTER
+#endif
+
+#ifdef USING_FRAME_POINTER
+# define MCOUNT_FRAME                   1       /* using frame = true  */
+#else
+# define MCOUNT_FRAME                   0       /* using frame = false */
+#endif
+
+ENTRY(function_hook)
         ret
-END(mcount)
+END(function_hook)
 
 ENTRY(ftrace_caller)
 
+#ifdef USING_FRAME_POINTER
+# ifdef CC_USING_FENTRY
+        /*
+         * Frame pointers are of ip followed by bp.
+         * Since fentry is an immediate jump, we are left with
+         * parent-ip, function-ip. We need to add a frame with
+         * parent-ip followed by ebp.
+         */
+        pushl   4(%esp)                         /* parent ip */
         pushl   %ebp
         movl    %esp, %ebp
-
+        pushl   2*4(%esp)                       /* function ip */
+# endif
+        /* For mcount, the function ip is directly above */
+        pushl   %ebp
+        movl    %esp, %ebp
+#endif
         pushl   %eax
         pushl   %ecx
         pushl   %edx
         pushl   $0                              /* Pass NULL as regs pointer */
-        movl    5*4(%esp), %eax
-        /* Copy original ebp into %edx */
+
+#ifdef USING_FRAME_POINTER
+        /* Load parent ebp into edx */
         movl    4*4(%esp), %edx
+#else
+        /* There's no frame pointer, load the appropriate stack addr instead */
+        lea     4*4(%esp), %edx
+#endif
+
+        movl    (MCOUNT_FRAME+4)*4(%esp), %eax  /* load the rip */
         /* Get the parent ip */
-        movl    0x4(%edx), %edx
+        movl    4(%edx), %edx                   /* edx has ebp */
+
         movl    function_trace_op, %ecx
         subl    $MCOUNT_INSN_SIZE, %eax
 
@@ -40,7 +82,14 @@ ftrace_call:
         popl    %edx
         popl    %ecx
         popl    %eax
+#ifdef USING_FRAME_POINTER
         popl    %ebp
+# ifdef CC_USING_FENTRY
+        addl    $4,%esp                         /* skip function ip */
+        popl    %ebp                            /* this is the orig bp */
+        addl    $4, %esp                        /* skip parent ip */
+# endif
+#endif
 .Lftrace_ret:
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 .globl ftrace_graph_call
@@ -81,6 +130,10 @@ ENTRY(ftrace_regs_caller)
         pushl   %edx
         pushl   %ecx
         pushl   %ebx
+#ifdef CC_USING_FENTRY
+        /* Load 4 off of the parent ip addr into ebp */
+        lea     14*4(%esp), %ebp
+#endif
 
         movl    12*4(%esp), %eax                /* Load ip (1st parameter) */
         subl    $MCOUNT_INSN_SIZE, %eax         /* Adjust ip */
@@ -119,7 +172,7 @@ GLOBAL(ftrace_regs_call)
         jmp     .Lftrace_ret
 #else /* ! CONFIG_DYNAMIC_FTRACE */
 
-ENTRY(mcount)
+ENTRY(function_hook)
         cmpl    $__PAGE_OFFSET, %esp
         jb      ftrace_stub                     /* Paging not enabled yet? */
 
@@ -151,9 +204,8 @@ ftrace_stub:
         popl    %ecx
         popl    %eax
         jmp     ftrace_stub
-END(mcount)
+END(function_hook)
 #endif /* CONFIG_DYNAMIC_FTRACE */
-EXPORT_SYMBOL(mcount)
 #endif /* CONFIG_FUNCTION_TRACER */
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
@@ -161,9 +213,15 @@ ENTRY(ftrace_graph_caller)
         pushl   %eax
         pushl   %ecx
         pushl   %edx
-        movl    0xc(%esp), %eax
+        movl    3*4(%esp), %eax
+        /* Even with frame pointers, fentry doesn't have one here */
+#ifdef CC_USING_FENTRY
+        lea     4*4(%esp), %edx
+        movl    $0, %ecx
+#else
         lea     0x4(%ebp), %edx
         movl    (%ebp), %ecx
+#endif
         subl    $MCOUNT_INSN_SIZE, %eax
         call    prepare_ftrace_return
         popl    %edx
@@ -176,7 +234,11 @@ END(ftrace_graph_caller)
 return_to_handler:
         pushl   %eax
         pushl   %edx
+#ifdef CC_USING_FENTRY
+        movl    $0, %eax
+#else
         movl    %ebp, %eax
+#endif
         call    ftrace_return_to_handler
         movl    %eax, %ecx
         popl    %edx