gentoo-overlay/sys-boot/grub/files/grub-0.97-Add-esp-to-list-of-clobbered-registers.patch

From 5a52ee4b5cd152fa4ccd1c1f938ce2eba652af52 Mon Sep 17 00:00:00 2001
From: Sergei Trofimovich <slyfox@gentoo.org>
Date: Mon, 14 Dec 2015 23:59:17 +0000
Subject: [PATCH] Add %esp to list of clobbered registers

GCC assumes that it can combine stacks from
outer
    grub_stage2()
and inner
    trampoline doit()
functions (optimisation -fcombine-stack-adjustments).

But doit() function clobbers %esp in inline
assebly statement as:

  asm volatile ("movl %%esp, %0\n\tmovl %1, %%esp\n"
               : "=&r" (realstack) : "r" (simstack));

which tricks gcc into computing invalid local variable
offsets from current %esp value.

Fix by hinting gcc about %esp change in clobber list.

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
---
 grub/asmstub.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/grub/asmstub.c b/grub/asmstub.c
index 6354806..44b056f 100644
--- a/grub/asmstub.c
+++ b/grub/asmstub.c
@@ -174,7 +174,7 @@ grub_stage2 (void)
     {
       /* Make sure our stack lives in the simulated memory area. */
       asm volatile ("movl %%esp, %0\n\tmovl %1, %%esp\n"
-		    : "=&r" (realstack) : "r" (simstack));
+		    : "=&r" (realstack) : "r" (simstack) : "%esp");
       
       /* Do a setjmp here for the stop command.  */
       if (! setjmp (env_for_exit))
@@ -191,7 +191,7 @@ grub_stage2 (void)
 	}
       
       /* Replace our stack before we use any local variables. */
-      asm volatile ("movl %0, %%esp\n" : : "r" (realstack));
+      asm volatile ("movl %0, %%esp\n" : : "r" (realstack) : "%esp");
     }
 
   assert (grub_scratch_mem == 0);
-- 
2.6.3