Add a checksum to jmp_buf on x86_64.

Bug: http://b/27856501
Bug: http://b/27417786
Change-Id: I541f5a7ce4972ef56b3f69e73927ca7df362609a

libc/arch-x86_64/bionic/setjmp.S

@@ -50,7 +50,7 @@
 // 7      pc
 // 8      sigflag/cookie  setjmp cookie in top 31 bits, signal mask flag in low bit
 // 9      sigmask         signal mask (includes rt signals as well)
-// 10     reserved
+// 10     checksum        checksum of the core registers, to give better error messages.
 
 #define _JB_RBX 0
 #define _JB_RBP 1
@@ -62,8 +62,10 @@
 #define _JB_PC 7
 #define _JB_SIGFLAG 8
 #define _JB_SIGMASK 9
+#define _JB_CHECKSUM 10
 
 #define MANGLE_REGISTERS 1
+
 .macro m_mangle_registers reg
 #if MANGLE_REGISTERS
   xorq \reg,%rbx
@@ -81,6 +83,12 @@
   m_mangle_registers \reg
 .endm
 
+.macro m_calculate_checksum dst, src
+  movq $0, \dst
+  .irp i,0,1,2,3,4,5,6,7
+    xorq (\i*8)(\src), \dst
+  .endr
+.endm
 
 ENTRY(setjmp)
   movl $1,%esi
@@ -131,6 +139,9 @@ ENTRY(sigsetjmp)
   movq %r11,(_JB_PC  * 8)(%rdi)
   m_unmangle_registers %rax
 
+  m_calculate_checksum %rax, %rdi
+  movq %rax, (_JB_CHECKSUM * 8)(%rdi)
+
   xorl %eax,%eax
   ret
 END(sigsetjmp)
@@ -140,6 +151,10 @@ ENTRY(siglongjmp)
   movq %rdi,%r12
   pushq %rsi // Push 'value'.
 
+  m_calculate_checksum %rax, %rdi
+  xorq (_JB_CHECKSUM * 8)(%rdi), %rax
+  jnz 3f
+
   // Do we need to restore the signal mask?
   movq (_JB_SIGFLAG * 8)(%rdi), %rdi
   pushq %rdi // Push cookie
@@ -185,6 +200,9 @@ ENTRY(siglongjmp)
 1:
   movq %r11,0(%rsp)
   ret
+
+3:
+  call PIC_PLT(__bionic_setjmp_checksum_mismatch)
 END(siglongjmp)
 
 ALIAS_SYMBOL(longjmp, siglongjmp)