Re: Clang/LLVM version requirements

[Tim Deegan <tim@xen.org>]

At 15:32 -0700 on 06 Sep (1346945573), Jeffrey Karrels wrote:
> Is there a required Clang and LLVM version one needs to do a 'make
> xen-dist clang=y'?
> 
> I recently tried and the process failed. I haven't begun debugging as
> I figured I would ask the obvious first. The build failed with the
> following:

Looks like the clang build has bitrotted a little - sorry.  It's too
late to fix this for 4.2 now but we can sort it out after we branch
(i.e. next week) and backport any build fixes for 4.2.1.

I have: 
  Debian clang version 3.0-6 (tags/RELEASE_30/final) (based on LLVM 3.0)
  Target: x86_64-pc-linux-gnu
  Thread model: posix

which can build _almost_ everything but chokes on a new .subsection rune
in inline asm.  It builds and boots with the change below.  Building
lto=y isn't working (GOLD is choking on the final link).  I'll look into
that next week.

Jan, would you object to some other way of checking for .bss in reloc.c?
Could we just objcopy it out so any BSS symbols make it fail at link
time?  In any case we probably ought to check for stray .data symbols too.

Cheers,

Tim.

diff -r ec23c2a11f6f xen/arch/x86/boot/reloc.c
--- a/xen/arch/x86/boot/reloc.c	Thu Sep 06 17:08:44 2012 +0100
+++ b/xen/arch/x86/boot/reloc.c	Fri Sep 07 09:30:13 2012 +0100
@@ -18,10 +18,7 @@ asm (
     "    call 1f                       \n"
     "1:  pop  %ebx                     \n"
     "    mov  %eax,alloc-1b(%ebx)      \n"
-    "    mov  $_end,%ecx               \n"  /* check that BSS is empty! */
-    "    sub  $__bss_start,%ecx        \n"
-    "    jz reloc                      \n"
-    "1:  jmp 1b                        \n"
+    "    jmp  reloc                    \n"
     );
 
 /* This is our data.  Because the code must be relocatable, no BSS is
@@ -30,9 +27,6 @@ asm (
 asm (
     "alloc:                            \n"
     "    .long 0                       \n"
-    "    .subsection 1                 \n"
-    "    .p2align 4, 0xcc              \n"
-    "    .subsection 0                 \n"
     );
 
 typedef unsigned int u32;