[PATCH] i386/x86-64: Work around gcc bug with noreturn functions in unwinder

Current gcc generates calls not jumps to noreturn functions. When that happens the
return address can point to the next function, which confuses the unwinder.

This patch works around it by marking asynchronous exception
frames in contrast normal call frames in the unwind information.  Then teach
the unwinder to decode this.

For normal call frames the unwinder now subtracts one from the address which avoids
this problem.  The standard libgcc unwinder uses the same trick.

It doesn't include adjustment of the printed address (i.e. for the original
example, it'd still be kernel_math_error+0 that gets displayed, but the
unwinder wouldn't get confused anymore.

This only works with binutils 2.6.17+ and some versions of H.J.Lu's 2.6.16
unfortunately because earlier binutils don't support .cfi_signal_frame

[AK: added automatic detection of the new binutils and wrote description]

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andi Kleen <ak@suse.de>

3 files changed, 12 insertions, 0 deletions

diff --git a/arch/x86_64/Makefile b/arch/x86_64/Makefile
index 2b8d07c70106..1c0f18d4f887 100644
--- a/arch/x86_64/Makefile
+++ b/arch/x86_64/Makefile
@@ -58,6 +58,10 @@ cflags-y += $(call cc-option,-mno-sse -mno-mmx -mno-sse2 -mno-3dnow,)
 cflags-y += $(call as-instr,.cfi_startproc\n.cfi_endproc,-DCONFIG_AS_CFI=1,)
 AFLAGS += $(call as-instr,.cfi_startproc\n.cfi_endproc,-DCONFIG_AS_CFI=1,)
 
+# is .cfi_signal_frame supported too?
+cflags-y += $(call as-instr,.cfi_startproc\n.cfi_signal_frame\n.cfi_endproc,-DCONFIG_AS_CFI_SIGNAL_FRAME=1,)
+AFLAGS += $(call as-instr,.cfi_startproc\n.cfi_signal_frame\n.cfi_endproc,-DCONFIG_AS_CFI_SIGNAL_FRAME=1,)
+
 cflags-$(CONFIG_CC_STACKPROTECTOR) += $(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-x86_64-has-stack-protector.sh $(CC) -fstack-protector )
 cflags-$(CONFIG_CC_STACKPROTECTOR_ALL) += $(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-x86_64-has-stack-protector.sh $(CC) -fstack-protector-all )
 
diff --git a/arch/x86_64/ia32/ia32entry.S b/arch/x86_64/ia32/ia32entry.S
index 32fd32bea07c..b4aa875e175b 100644
--- a/arch/x86_64/ia32/ia32entry.S
+++ b/arch/x86_64/ia32/ia32entry.S
@@ -71,6 +71,7 @@
  */     
 ENTRY(ia32_sysenter_target)
         CFI_STARTPROC32 simple
+        CFI_SIGNAL_FRAME
         CFI_DEF_CFA     rsp,0
         CFI_REGISTER    rsp,rbp
         swapgs
@@ -186,6 +187,7 @@ ENDPROC(ia32_sysenter_target)
  */     
 ENTRY(ia32_cstar_target)
         CFI_STARTPROC32 simple
+        CFI_SIGNAL_FRAME
         CFI_DEF_CFA     rsp,PDA_STACKOFFSET
         CFI_REGISTER    rip,rcx
         /*CFI_REGISTER  rflags,r11*/
@@ -293,6 +295,7 @@ ia32_badarg:
 
 ENTRY(ia32_syscall)
         CFI_STARTPROC   simple
+        CFI_SIGNAL_FRAME
         CFI_DEF_CFA     rsp,SS+8-RIP
         /*CFI_REL_OFFSET        ss,SS-RIP*/
         CFI_REL_OFFSET  rsp,RSP-RIP
@@ -370,6 +373,7 @@ ENTRY(ia32_ptregs_common)
         popq %r11
         CFI_ENDPROC
         CFI_STARTPROC32 simple
+        CFI_SIGNAL_FRAME
         CFI_DEF_CFA     rsp,SS+8-ARGOFFSET
         CFI_REL_OFFSET  rax,RAX-ARGOFFSET
         CFI_REL_OFFSET  rcx,RCX-ARGOFFSET
diff --git a/arch/x86_64/kernel/entry.S b/arch/x86_64/kernel/entry.S
index ea32688386fd..4cbc65290ae7 100644
--- a/arch/x86_64/kernel/entry.S
+++ b/arch/x86_64/kernel/entry.S
@@ -123,6 +123,7 @@
         .macro  CFI_DEFAULT_STACK start=1
         .if \start
         CFI_STARTPROC   simple
+        CFI_SIGNAL_FRAME
         CFI_DEF_CFA     rsp,SS+8
         .else
         CFI_DEF_CFA_OFFSET SS+8
@@ -207,6 +208,7 @@ END(ret_from_fork)
 
 ENTRY(system_call)
         CFI_STARTPROC   simple
+        CFI_SIGNAL_FRAME
         CFI_DEF_CFA     rsp,PDA_STACKOFFSET
         CFI_REGISTER    rip,rcx
         /*CFI_REGISTER  rflags,r11*/
@@ -324,6 +326,7 @@ END(system_call)
  */     
 ENTRY(int_ret_from_sys_call)
         CFI_STARTPROC   simple
+        CFI_SIGNAL_FRAME
         CFI_DEF_CFA     rsp,SS+8-ARGOFFSET
         /*CFI_REL_OFFSET        ss,SS-ARGOFFSET*/
         CFI_REL_OFFSET  rsp,RSP-ARGOFFSET
@@ -484,6 +487,7 @@ END(stub_rt_sigreturn)
  */
         .macro _frame ref
         CFI_STARTPROC simple
+        CFI_SIGNAL_FRAME
         CFI_DEF_CFA rsp,SS+8-\ref
         /*CFI_REL_OFFSET ss,SS-\ref*/
         CFI_REL_OFFSET rsp,RSP-\ref