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>

diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index 87a72c66ce27759d3cd087e0cf2abd378f144531..a914411bced5defb4179628c9b0049d68a360ab0 100644 (file)
--- 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