[xen staging] x86/build32: Discard all orphaned sections

[patchbot@xxxxxxx]

commit 24f94fca23ad7c45806a1428331e1d602dfd8604
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Tue May 12 19:18:37 2020 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Wed May 13 20:33:42 2020 +0100

    x86/build32: Discard all orphaned sections
    
    Linkers may put orphaned sections ahead of .text, which breaks the calling
    requirements.  A concrete example is Ubuntu's GCC-9 default of enabling
    -fcf-protection which causes us to try and execute .note.gnu.properties 
during
    Xen's boot.
    
    Put .got.plt in its own section as it specifically needs preserving from the
    linkers point of view, and discard everything else.  This will hopefully be
    more robust to other unexpected toolchain properties.
    
    Fixes boot from an Ubuntu build of Xen.
    
    Reported-by: Jason Andryuk <jandryuk@xxxxxxxxx>
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Tested-by: Jason Andryuk <jandryuk@xxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/boot/build32.lds | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/boot/build32.lds b/xen/arch/x86/boot/build32.lds
index da35aee910..97454b40ff 100644
--- a/xen/arch/x86/boot/build32.lds
+++ b/xen/arch/x86/boot/build32.lds
@@ -31,7 +31,7 @@ SECTIONS
         *(.bss.*)
   }
 
-  /DISCARD/ : {
+  .got.plt : {
         /*
          * PIC/PIE executable contains .got.plt section even if it is not 
linked
          * with dynamic libraries. In such case it is just placeholder for
@@ -47,6 +47,14 @@ SECTIONS
          *
          * Please check build32.mk for more details.
          */
-        /* *(.got.plt) */
+        *(.got.plt)
+  }
+
+  /DISCARD/ : {
+        /*
+         * Discard everything else, to prevent linkers from putting
+         * orphaned sections ahead of .text, which needs to be first.
+         */
+        *(*)
   }
 }
--
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