[PATCH] ARM: VDSO: fix regression with toolchains lacking ld.bfd executable

[Nathan Lynch]

The Sourcery CodeBench Lite 2014.05 toolchain (gcc 4.8.3, binutils
2.24.51) has a GCC which implements -fuse-ld, and it doesn't include
the gold linker, but it lacks an ld.bfd executable in its
installation.  This means that passing -fuse-ld=bfd fails with:

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

Arguably this is a deficiency in the toolchain, but I suspect it's
commonly used enough that it's worth accommodating: just use
cc-ldoption (to cause a link attempt) instead of cc-option to test
whether we can use -fuse-ld.  So -fuse-ld=bfd won't be used with this
toolchain, but the build will rightly succeed, just as it does for
toolchains which don't implement -fuse-ld (and don't use gold as the
default linker).

Note: this will change the failure mode for a corner case I was trying
to handle in d2b30cd4b722, where the toolchain defaults to the gold
linker and the BFD linker is not found in PATH, from:

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

i.e. the BFD linker is not found, to:

      OBJCOPY arch/arm/vdso/vdso.so
    BFD: arch/arm/vdso/vdso.so: Not enough room for program headers, try
    linking with -N

that is, we fail to prevent gold from being used as the linker, and it
produces an object that objcopy can't digest.

Reported-by: Baruch Siach <baruch at tkos.co.il>
Tested-by: Baruch Siach <baruch at tkos.co.il>
Fixes: d2b30cd4b722 ("ARM: 8384/1: VDSO: force use of BFD linker")
Cc: stable at vger.kernel.org
Signed-off-by: Nathan Lynch <nathan_lynch at mentor.com>
---
 arch/arm/vdso/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/vdso/Makefile b/arch/arm/vdso/Makefile
index 9d259d94e429..1160434eece0 100644
--- a/arch/arm/vdso/Makefile
+++ b/arch/arm/vdso/Makefile
@@ -14,7 +14,7 @@ VDSO_LDFLAGS += -Wl,-z,max-page-size=4096 -Wl,-z,common-page-size=4096
 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)
+VDSO_LDFLAGS += $(call cc-ldoption, -fuse-ld=bfd)
 
 obj-$(CONFIG_VDSO) += vdso.o
 extra-$(CONFIG_VDSO) += vdso.lds
-- 
2.1.0