linux-kernel - [PATCH 4.1 33/78] ARM: 8384/1: VDSO: force use of BFD linker

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Date:	Fri, 11 Sep 2015 15:49:34 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Stefan Agner <stefan@...er.ch>,
	Nathan Lynch <nathan_lynch@...tor.com>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Alexander Kochetkov <al.kochet@...il.com>
Subject: [PATCH 4.1 33/78] ARM: 8384/1: VDSO: force use of BFD linker

4.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nathan Lynch <nathan_lynch@...tor.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@...er.ch>
Signed-off-by: Nathan Lynch <nathan_lynch@...tor.com>
Signed-off-by: Russell King <rmk+kernel@....linux.org.uk>
Cc: Alexander Kochetkov <al.kochet@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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


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