linux-kernel - Re: [PATCH 2/4] x86/kprobes: Fix frame pointer annotations

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Date:   Wed, 8 May 2019 14:40:02 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Nicolai Stange <nstange@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Shuah Khan <shuah@...nel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Juergen Gross <jgross@...e.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nayna Jain <nayna@...ux.ibm.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Joerg Roedel <jroedel@...e.de>,
        linux-kselftest@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH 2/4] x86/kprobes: Fix frame pointer annotations

On Wed, May 08, 2019 at 02:04:16PM +0200, Peter Zijlstra wrote:
> On Wed, May 08, 2019 at 06:54:16AM -0500, Josh Poimboeuf wrote:

> > We should put these macros in a header file somewhere (including
> > stringified versions).
> 
> Probably a good idea. I'll frob them into asm/frame.h.

---
Subject: x86: Move ENCODE_FRAME_POINTER to asm/frame.h
From: Peter Zijlstra <peterz@...radead.org>
Date: Wed May 8 14:30:48 CEST 2019

In preparation for wider use, move the ENCODE_FRAME_POINTER macros to
a common header and provide inline asm versions.

These macros are used to encode a pt_regs frame for the unwinder; see
unwind_frame.c:decode_frame_pointer().

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/entry/calling.h     |   15 --------------
 arch/x86/entry/entry_32.S    |   16 --------------
 arch/x86/include/asm/frame.h |   46 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 46 insertions(+), 31 deletions(-)

--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -172,21 +172,6 @@ For 32-bit we have the following convent
 	.endif
 .endm
 
-/*
- * This is a sneaky trick to help the unwinder find pt_regs on the stack.  The
- * frame pointer is replaced with an encoded pointer to pt_regs.  The encoding
- * is just setting the LSB, which makes it an invalid stack address and is also
- * a signal to the unwinder that it's a pt_regs pointer in disguise.
- *
- * NOTE: This macro must be used *after* PUSH_AND_CLEAR_REGS because it corrupts
- * the original rbp.
- */
-.macro ENCODE_FRAME_POINTER ptregs_offset=0
-#ifdef CONFIG_FRAME_POINTER
-	leaq 1+\ptregs_offset(%rsp), %rbp
-#endif
-.endm
-
 #ifdef CONFIG_PAGE_TABLE_ISOLATION
 
 /*
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -246,22 +246,6 @@
 .Lend_\@:
 .endm
 
-/*
- * This is a sneaky trick to help the unwinder find pt_regs on the stack.  The
- * frame pointer is replaced with an encoded pointer to pt_regs.  The encoding
- * is just clearing the MSB, which makes it an invalid stack address and is also
- * a signal to the unwinder that it's a pt_regs pointer in disguise.
- *
- * NOTE: This macro must be used *after* SAVE_ALL because it corrupts the
- * original rbp.
- */
-.macro ENCODE_FRAME_POINTER
-#ifdef CONFIG_FRAME_POINTER
-	mov %esp, %ebp
-	andl $0x7fffffff, %ebp
-#endif
-.endm
-
 .macro RESTORE_INT_REGS
 	popl	%ebx
 	popl	%ecx
--- a/arch/x86/include/asm/frame.h
+++ b/arch/x86/include/asm/frame.h
@@ -22,6 +22,39 @@
 	pop %_ASM_BP
 .endm
 
+#ifdef CONFIG_X86_64
+/*
+ * This is a sneaky trick to help the unwinder find pt_regs on the stack.  The
+ * frame pointer is replaced with an encoded pointer to pt_regs.  The encoding
+ * is just setting the LSB, which makes it an invalid stack address and is also
+ * a signal to the unwinder that it's a pt_regs pointer in disguise.
+ *
+ * NOTE: This macro must be used *after* PUSH_AND_CLEAR_REGS because it corrupts
+ * the original rbp.
+ */
+.macro ENCODE_FRAME_POINTER ptregs_offset=0
+#ifdef CONFIG_FRAME_POINTER
+	leaq 1+\ptregs_offset(%rsp), %rbp
+#endif
+.endm
+#else /* !CONFIG_X86_64 */
+/*
+ * This is a sneaky trick to help the unwinder find pt_regs on the stack.  The
+ * frame pointer is replaced with an encoded pointer to pt_regs.  The encoding
+ * is just clearing the MSB, which makes it an invalid stack address and is also
+ * a signal to the unwinder that it's a pt_regs pointer in disguise.
+ *
+ * NOTE: This macro must be used *after* SAVE_ALL because it corrupts the
+ * original ebp.
+ */
+.macro ENCODE_FRAME_POINTER
+#ifdef CONFIG_FRAME_POINTER
+	mov %esp, %ebp
+	andl $0x7fffffff, %ebp
+#endif
+.endm
+#endif /* CONFIG_X86_64 */
+
 #else /* !__ASSEMBLY__ */
 
 #define FRAME_BEGIN				\
@@ -30,6 +63,19 @@
 
 #define FRAME_END "pop %" _ASM_BP "\n"
 
+#ifdef CONFIG_FRAME_POINTER
+#ifdef CONFIG_X86_64
+#define ENCODE_FRAME_POINTER			\
+	"lea 1(%rsp), %rbp\n\t"
+#else /* !CONFIG_X86_64 */
+#define ENCODE_FRAME_POINTER			\
+	"movl %esp, %ebp\n\t"			\
+	"andl $0x7fffffff, %ebp\n\t"
+#endif /* CONFIG_X86_64 */
+#else /* CONFIG_FRAME_POINTER */
+#define ENCODE_FRAME_POINTER
+#endif /* CONFIG_FRAME_POINTER */
+
 #endif /* __ASSEMBLY__ */
 
 #define FRAME_OFFSET __ASM_SEL(4, 8)