[grub2] Fix module trampoline for ppc.

Mon May 14 20:51:34 UTC 2012

commit ed858ec792ab8eb648bdd139613b2c5bf1a83208
Author: Peter Jones <pjones at redhat.com>
Date:   Mon May 14 16:51:08 2012 -0400

    Fix module trampoline for ppc.

 grub-2.00-Fix-module-trampoline-for-ppc.patch |  120 +++++++++++++++++++++++++
 grub2.spec                                    |    4 +
 2 files changed, 124 insertions(+), 0 deletions(-)
---

diff --git a/grub-2.00-Fix-module-trampoline-for-ppc.patch b/grub-2.00-Fix-module-trampoline-for-ppc.patch
new file mode 100644
index 0000000..60cde3a
--- /dev/null
+++ b/grub-2.00-Fix-module-trampoline-for-ppc.patch
@@ -0,0 +1,120 @@
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+Message-ID: <1336966957.6727.15.camel at pasglop>
+Subject: [PATCH] grub: Fix module trampoline for powerpc
+From: Benjamin Herrenschmidt <benh at au1.ibm.com>
+To: Brent Baude <baude at us.ibm.com>, pjones at fedoraproject.org
+Cc: hamzy at us.ibm.com, Josh Boyer <jwboyer at gmail.com>
+Date: Mon, 14 May 2012 13:42:37 +1000
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+[ --- snip --- ]
+
+Not sure who to send that to, I picked Peter as he's in
+the rpm log as author of the of the powerpc patches,
+feel free to do whatever with that one, it should ultimately
+go to upstream grub I suppose ...
+
+Without this, grub doesn't work for me at all with fc17 beta
+
+[ --- snip --- ]
+
+The trampoline generated by grub powerpc's dl.c to call from
+modules into the main grub code uses r0 as a scratch register.
+
+However, nowadays, gcc can (and will) generate function calls
+to spill registers to the stack (well, it's even stupid enough
+to do it when there's only one register to save ! go figure....)
+
+Those calls happen during the function prolog, before the
+return address has been saved on the stack, typically it's held
+in r0 at this stage. Since those calls will hit the trampoline
+in grub, which clobbers r0, this will clobber the return address
+and cause a crash.
+
+This patch changes the trampolines to use r12 instead which
+is safe to use in our case.
+
+Note: It might be better to actually link those low level gcc
+support functions statically into the modules but that's beyond
+the level of grub hacking I'm prepared to do today.
+
+Signed-off-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>
+---
+diff --git a/grub-core/kern/powerpc/dl.c b/grub-core/kern/powerpc/dl.c
+index b8a2b50..0a8ec85 100644
+--- a/grub-core/kern/powerpc/dl.c
++++ b/grub-core/kern/powerpc/dl.c
+@@ -89,9 +89,9 @@ struct trampoline
+ 
+ static const struct trampoline trampoline_template = 
+   {
+-    0x3c000000,
+-    0x60000000,
+-    0x7c0903a6,
++    0x3d800000,
++    0x618c0000,
++    0x7d8903a6,
+     0x4e800420,
+   };
+ 
+
+
diff --git a/grub2.spec b/grub2.spec
index deebae9..0528d68 100644
--- a/grub2.spec
+++ b/grub2.spec
@@ -41,6 +41,7 @@ Patch4:		grub-1.99-Fix-tests-of-zeroed-partition.patch
 Patch5:		grub-1.99-ppc-terminfo.patch
 Patch7:		grub-2.00~beta4-add-support-for-PowerMac-HFS-partitions.patch
 Patch8:		grub2-2.0-no-png-in-texi.patch
+Patch9:		grub-2.00-Fix-module-trampoline-for-ppc.patch
 
 BuildRoot:      %{_tmppath}/%{name}-%{version}-%{release}-root-%(%{__id_u} -n)
 
@@ -388,6 +389,9 @@ fi
 %endif
 
 %changelog
+* Mon May 14 2012 Peter Jones <pjones at redhat.com> - 2.0-0.27.beta5
+- Fix module trampolining on ppc (benh)
+
 * Thu May 10 2012 Peter Jones <pjones at redhat.com> - 2.0-0.27.beta5
 - Fix license of theme (mizmo)
   Resolves: rhbz#820713
