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SubjectRe: [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@infradead.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@infradead.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)
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