powerpc: Fix build bug with binutils < 2.18 and GCC < 4.2

binutils < 2.18 has a bug that makes it misbehave when taking an
ELF file with all segments at load address 0 as input.  This
happens when running "strip" on vmlinux, because of the AT() magic
in this linker script.  People using GCC >= 4.2 won't run into
this problem, because the "build-id" support will put some data
into the "notes" segment (at a non-zero load address).

To work around this, we force some data into both the "dummy"
segment and the kernel segment, so the dummy segment will get a
non-zero load address.  It's not enough to always create the
"notes" segment, since if nothing gets assigned to it, its load
address will be zero.

Signed-off-by: Segher Boessenkool <segher@kernel.crashing.org>
Tested-By: Milton Miller <miltonm@bga.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 28 insertions, 3 deletions

diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index 87a72c66ce27..a914411bced5 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -9,6 +9,25 @@
 
 ENTRY(_stext)
 
+PHDRS {
+        kernel PT_LOAD FLAGS(7); /* RWX */
+        notes PT_NOTE FLAGS(0);
+        dummy PT_NOTE FLAGS(0);
+
+        /* binutils < 2.18 has a bug that makes it misbehave when taking an
+           ELF file with all segments at load address 0 as input.  This
+           happens when running "strip" on vmlinux, because of the AT() magic
+           in this linker script.  People using GCC >= 4.2 won't run into
+           this problem, because the "build-id" support will put some data
+           into the "notes" segment (at a non-zero load address).
+
+           To work around this, we force some data into both the "dummy"
+           segment and the kernel segment, so the dummy segment will get a
+           non-zero load address.  It's not enough to always create the
+           "notes" segment, since if nothing gets assigned to it, its load
+           address will be zero.  */
+}
+
 #ifdef CONFIG_PPC64
 OUTPUT_ARCH(powerpc:common64)
 jiffies = jiffies_64;
@@ -50,7 +69,7 @@ SECTIONS
                 . = ALIGN(PAGE_SIZE);
                 _etext = .;
                 PROVIDE32 (etext = .);
-        }
+        } :kernel
 
         /* Read-only data */
         RODATA
@@ -62,7 +81,13 @@ SECTIONS
                 __stop___ex_table = .;
         }
 
-        NOTES
+        NOTES :kernel :notes
+
+        /* The dummy segment contents for the bug workaround mentioned above
+           near PHDRS.  */
+        .dummy : {
+                LONG(0xf177)
+        } :kernel :dummy
 
 /*
  * Init sections discarded at runtime
@@ -74,7 +99,7 @@ SECTIONS
                 _sinittext = .;
                 INIT_TEXT
                 _einittext = .;
-        }
+        } :kernel
 
         /* .exit.text is discarded at runtime, not link time,
          * to deal with references from __bug_table