Patch "ARM: 8384/1: VDSO: force use of BFD linker" has been added to the 4.1-stable tree

Patch "ARM: 8384/1: VDSO: force use of BFD linker" has been added to the 4.1-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    ARM: 8384/1: VDSO: force use of BFD linker

to the 4.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     arm-8384-1-vdso-force-use-of-bfd-linker.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From d2b30cd4b7223a96e606dfc8120626f66d81e091 Mon Sep 17 00:00:00 2001
From: Nathan Lynch <nathan_lynch@mentor.com>
Date: Wed, 3 Jun 2015 00:41:15 +0100
Subject: ARM: 8384/1: VDSO: force use of BFD linker

From: Nathan Lynch <nathan_lynch@mentor.com>

commit d2b30cd4b7223a96e606dfc8120626f66d81e091 upstream.

When using a toolchain with gold as the default linker, the VDSO build
fails:

  VDSO    arch/arm/vdso/vdso.so.raw
  HOSTCC  arch/arm/vdso/vdsomunge
  MUNGE   arch/arm/vdso/vdso.so.dbg
  OBJCOPY arch/arm/vdso/vdso.so
BFD: arch/arm/vdso/vdso.so: Not enough room for program headers, try
linking with -N

For whatever reason, ld.gold is omitting an exidx program header that
ld.bfd emits, and even when I work around that, I don't get a working
VDSO.

For now, instead of supporting gold (which will fail to link the
kernel anyway since it does not implement --pic-veneer), direct the
compiler to use the traditional bfd linker.  This is accomplished by
using -fuse-ld, which is implemented in GCC 4.8 and later.

Note: one limitation of this is that if the toolchain is configured
to use gold by default, and the bfd linker is not in $PATH, the VDSO
build will fail:

  VDSO    arch/arm/vdso/vdso.so.raw
collect2: fatal error: cannot find 'ld'

This will happen if CROSS_COMPILE begins with a path such as
/opt/bin/arm-linux-gnu- but /opt/bin is not in $PATH.  This is
considered an acceptable corner-case limitation and is easily worked
around.

Additonal note: we use cc-option instead of cc-ldoption so that
-fuse-ld=bfd is placed in the command line if the compiler recognizes
the option.  Using cc-ldoption results in an attempt to link, which
fails in the situation just described, causing -fuse-ld=bfd to be
omitted and gold to be used for the VDSO link, which is what we're
trying to prevent.

Reported-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Nathan Lynch <nathan_lynch@mentor.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: Alexander Kochetkov <al.kochet@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/arm/vdso/Makefile |    1 +
 1 file changed, 1 insertion(+)

--- a/arch/arm/vdso/Makefile
+++ b/arch/arm/vdso/Makefile
@@ -14,6 +14,7 @@ VDSO_LDFLAGS += -Wl,-z,max-page-size=409
 VDSO_LDFLAGS += -nostdlib -shared
 VDSO_LDFLAGS += $(call cc-ldoption, -Wl$(comma)--hash-style=sysv)
 VDSO_LDFLAGS += $(call cc-ldoption, -Wl$(comma)--build-id)
+VDSO_LDFLAGS += $(call cc-option, -fuse-ld=bfd)
 
 obj-$(CONFIG_VDSO) += vdso.o
 extra-$(CONFIG_VDSO) += vdso.lds


Patches currently in stable-queue which might be from nathan_lynch@mentor.com are

queue-4.1/arm-8384-1-vdso-force-use-of-bfd-linker.patch
queue-4.1/arm-8385-1-vdso-group-link-options.patch