[PATCH] x86_64: add CFI annotations to swapcontext (bug 34575)

[Andreas Schwab <schwab@suse.de>]

The annotations allow the unwinder to always find the return address in
one of the contexts.  Also mark __start_context as outermost frame, which
is used by makecontext as the return address for the context.
---
 .../unix/sysv/linux/x86_64/__start_context.S  |  2 ++
 sysdeps/unix/sysv/linux/x86_64/swapcontext.S  | 20 +++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/sysdeps/unix/sysv/linux/x86_64/__start_context.S b/sysdeps/unix/sysv/linux/x86_64/__start_context.S
index 2eb5e16d02..5943a84f7c 100644
--- a/sysdeps/unix/sysv/linux/x86_64/__start_context.S
+++ b/sysdeps/unix/sysv/linux/x86_64/__start_context.S
@@ -75,6 +75,8 @@ END(__push___start_context)
 
 
 ENTRY(__start_context)
+	/* Mark as outermost frame.  */
+	cfi_undefined (rip)
 	/* This removes the parameters passed to the function given to
 	   'makecontext' from the stack.  RBX contains the address
 	   on the stack pointer for the next context.  */
diff --git a/sysdeps/unix/sysv/linux/x86_64/swapcontext.S b/sysdeps/unix/sysv/linux/x86_64/swapcontext.S
index 4c9c08a828..258c75562c 100644
--- a/sysdeps/unix/sysv/linux/x86_64/swapcontext.S
+++ b/sysdeps/unix/sysv/linux/x86_64/swapcontext.S
@@ -54,6 +54,14 @@ ENTRY(__swapcontext)
 	movq	%rcx, oRIP(%rdi)
 	leaq	8(%rsp), %rcx		/* Exclude the return address.  */
 	movq	%rcx, oRSP(%rdi)
+	cfi_def_cfa (%rdi, oRIP)
+	cfi_offset (%rbx, oRBX-oRIP)
+	cfi_offset (%rbp, oRBP-oRIP)
+	cfi_offset (%r12, oR12-oRIP)
+	cfi_offset (%r13, oR13-oRIP)
+	cfi_offset (%r14, oR14-oRIP)
+	cfi_offset (%r15, oR15-oRIP)
+	cfi_offset (%rip, 0)
 
 	/* We have separate floating-point register content memory on the
 	   stack.  We use the __fpregs_mem block in the context.  Set the
@@ -68,6 +76,7 @@ ENTRY(__swapcontext)
 	/* The syscall destroys some registers, save them.  */
 	movq	%rsi, %r12
 	movq	%rdi, %r9
+	cfi_def_cfa (%r9, oRIP)
 
 	/* Save the current signal mask and install the new one with
 	   rt_sigprocmask (SIG_BLOCK, newset, oldset,_NSIG/8).  */
@@ -84,6 +93,7 @@ ENTRY(__swapcontext)
 	   but leaving RDI and RSI available for use later can avoid
 	   shuffling values.  */
 	movq	%r12, %rdx
+	cfi_def_cfa (%rdx, oRIP)
 
 	/* Restore the floating-point context.  Not the registers, only the
 	   rest.  */
@@ -99,6 +109,12 @@ ENTRY(__swapcontext)
 	movq	oR13(%rdx), %r13
 	movq	oR14(%rdx), %r14
 	movq	oR15(%rdx), %r15
+	cfi_restore (%rbx)
+	cfi_restore (%rbp)
+	cfi_restore (%r12)
+	cfi_restore (%r13)
+	cfi_restore (%r14)
+	cfi_restore (%r15)
 
 #if SHSTK_ENABLED
 	/* Check if shadow stack is enabled.  */
@@ -191,6 +207,7 @@ L(skip_unwind_shadow_stack):
 
 	/* Get the return address set with getcontext.  */
 	movq	oRIP(%rdx), %r10
+	cfi_register (%rip, %r10)
 
 	/* Setup finally %rdx.  */
 	movq	oRDX(%rdx), %rdx
@@ -210,6 +227,7 @@ L(skip_unwind_shadow_stack):
 L(jmp):
 	/* Jump to the new context directly.  */
 	jmp	*%r10
+	cfi_offset (%rip, 0)
 
 L(no_shstk):
 #endif
@@ -217,6 +235,8 @@ L(no_shstk):
 	getcontext.  Therefore push the address on the stack.  */
 	movq	oRIP(%rdx), %rcx
 	pushq	%rcx
+	cfi_def_cfa (%rsp, 8)
+	cfi_offset (%rip, -8)
 
 	/* Setup registers used for passing args.  */
 	movq	oRDI(%rdx), %rdi
-- 
2.55.0


-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."