From: Josh Poimboeuf <jpoimboe@redhat.com>
Date: Fri, 8 Nov 2019 16:51:00 -0600
Subject: ftrace/x86: Tell objtool to ignore nondeterministic ftrace stack
layout
Git-commit: 77ac117b3a82251b109ffc5daf7d1c5392734be3
Patch-mainline: v5.5-rc1
References: bsc#1177028
Objtool complains about the new ftrace direct trampoline code:
arch/x86/kernel/ftrace_64.o: warning: objtool: ftrace_regs_caller()+0x190: stack state mismatch: cfa1=7+16 cfa2=7+24
Typically, code has a deterministic stack layout, such that at a given
instruction address, the stack frame size is always the same.
That's not the case for the new ftrace_regs_caller() code after it
adjusts the stack for the direct case. Just plead ignorance and assume
it's always the non-direct path. Note this creates a tiny window for
ORC to get confused.
Link: http://lkml.kernel.org/r/20191108225100.ea3bhsbdf6oerj6g@treble
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Miroslav Benes <mbenes@suse.cz>
---
arch/x86/include/asm/unwind_hints.h | 8 ++++++++
arch/x86/kernel/ftrace_64.S | 12 +++++++++++-
2 files changed, 19 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/unwind_hints.h b/arch/x86/include/asm/unwind_hints.h
index 0bcdb1279361..f5e2eb12cb71 100644
--- a/arch/x86/include/asm/unwind_hints.h
+++ b/arch/x86/include/asm/unwind_hints.h
@@ -86,6 +86,14 @@
UNWIND_HINT sp_offset=\sp_offset
.endm
+.macro UNWIND_HINT_SAVE
+ UNWIND_HINT type=UNWIND_HINT_TYPE_SAVE
+.endm
+
+.macro UNWIND_HINT_RESTORE
+ UNWIND_HINT type=UNWIND_HINT_TYPE_RESTORE
+.endm
+
#else /* !__ASSEMBLY__ */
#define UNWIND_HINT(sp_reg, sp_offset, type, end) \
diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index 6ac7ff304886..b33abdd0a2db 100644
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -178,6 +178,8 @@ ENTRY(ftrace_regs_caller)
/* Save the current flags before any operations that can change them */
pushfq
+ UNWIND_HINT_SAVE
+
/* added 8 bytes to save flags */
save_mcount_regs 8
/* save_mcount_regs fills in first two parameters */
@@ -250,8 +252,16 @@ GLOBAL(ftrace_regs_call)
1: restore_mcount_regs
+2:
+ /*
+ * The stack layout is nondetermistic here, depending on which path was
+ * taken. This confuses objtool and ORC, rightfully so. For now,
+ * pretend the stack always looks like the non-direct case.
+ */
+ UNWIND_HINT_RESTORE
+
/* Restore flags */
-2: popfq
+ popfq
/*
* As this jmp to ftrace_epilogue can be a short jump