Revert upstream commit 15eab1e3e891 ("i386: Don't unnecessarily save and
restore EAX, ECX and EDX [BZ# 25262]"). It breaks libunwind8.

--- a/sysdeps/unix/sysv/linux/i386/getcontext.S
+++ b/sysdeps/unix/sysv/linux/i386/getcontext.S
@@ -25,7 +25,13 @@ ENTRY(__getcontext)
 	/* Load address of the context data structure.  */
 	movl	4(%esp), %eax
 
-	/* Save the preserved register values and the return address.  */
+	/* Return value of getcontext.  EAX is the only register whose
+	   value is not preserved.  */
+	movl	$0, oEAX(%eax)
+
+	/* Save the 32-bit register values and the return address.  */
+	movl	%ecx, oECX(%eax)
+	movl	%edx, oEDX(%eax)
 	movl	%edi, oEDI(%eax)
 	movl	%esi, oESI(%eax)
 	movl	%ebp, oEBP(%eax)
--- a/sysdeps/unix/sysv/linux/i386/setcontext.S
+++ b/sysdeps/unix/sysv/linux/i386/setcontext.S
@@ -64,19 +64,22 @@ ENTRY(__setcontext)
 	cfi_offset (esi, oESI)
 	cfi_offset (ebp, oEBP)
 	cfi_offset (ebx, oEBX)
+	cfi_offset (edx, oEDX)
+	cfi_offset (ecx, oECX)
 	movl	oESP(%eax), %esp
 
 	/* Push the return address on the new stack so we can return there.  */
 	pushl	%ecx
 
-	/* Load the values of all the preserved registers (except ESP).  */
+	/* Load the values of all the 32-bit registers (except ESP).
+	   Since we are loading from EAX, it must be last.  */
 	movl	oEDI(%eax), %edi
 	movl	oESI(%eax), %esi
 	movl	oEBP(%eax), %ebp
 	movl	oEBX(%eax), %ebx
-
-	/* All done, return 0 for success.  */
-	xorl	%eax, %eax
+	movl	oEDX(%eax), %edx
+	movl	oECX(%eax), %ecx
+	movl	oEAX(%eax), %eax
 
 	/* End FDE here, we fall into another context.  */
 	cfi_endproc
--- a/sysdeps/unix/sysv/linux/i386/swapcontext.S
+++ b/sysdeps/unix/sysv/linux/i386/swapcontext.S
@@ -25,7 +25,13 @@ ENTRY(__swapcontext)
 	/* Load address of the context data structure we save in.  */
 	movl	4(%esp), %eax
 
-	/* Save the preserved register values and the return address.  */
+	/* Return value of swapcontext.  EAX is the only register whose
+	   value is not preserved.  */
+	movl	$0, oEAX(%eax)
+
+	/* Save the 32-bit register values and the return address.  */
+	movl	%ecx, oECX(%eax)
+	movl	%edx, oEDX(%eax)
 	movl	%edi, oEDI(%eax)
 	movl	%esi, oESI(%eax)
 	movl	%ebp, oEBP(%eax)
@@ -84,14 +90,15 @@ ENTRY(__swapcontext)
 	/* Push the return address on the new stack so we can return there.  */
 	pushl	%ecx
 
-	/* Load the values of all the preserved registers (except ESP).  */
+	/* Load the values of all the 32-bit registers (except ESP).
+	   Since we are loading from EAX, it must be last.  */
 	movl	oEDI(%eax), %edi
 	movl	oESI(%eax), %esi
 	movl	oEBP(%eax), %ebp
 	movl	oEBX(%eax), %ebx
-
-	/* All done, return 0 for success.  */
-	xorl	%eax, %eax
+	movl	oEDX(%eax), %edx
+	movl	oECX(%eax), %ecx
+	movl	oEAX(%eax), %eax
 
 	/* The following 'ret' will pop the address of the code and jump
 	   to it.  */
--- a/sysdeps/unix/sysv/linux/i386/ucontext_i.sym
+++ b/sysdeps/unix/sysv/linux/i386/ucontext_i.sym
@@ -21,6 +21,9 @@ oESI		mreg (ESI)
 oEBP		mreg (EBP)
 oESP		mreg (ESP)
 oEBX		mreg (EBX)
+oEDX		mreg (EDX)
+oECX		mreg (ECX)
+oEAX		mreg (EAX)
 oEIP		mreg (EIP)
 oFPREGS		mcontext (fpregs)
 oSIGMASK	ucontext (uc_sigmask)