[PATCH] vDSO hash-style fix

The latest toolchains can produce a new ELF section in DSOs and
dynamically-linked executables.  The new section ".gnu.hash" replaces
".hash", and allows for more efficient runtime symbol lookups by the
dynamic linker.  The new ld option --hash-style={sysv|gnu|both} controls
whether to produce the old ".hash", the new ".gnu.hash", or both.  In some
new systems such as Fedora Core 6, gcc by default passes --hash-style=gnu
to the linker, so that a standard invocation of "gcc -shared" results in
producing a DSO with only ".gnu.hash".  The new ".gnu.hash" sections need
to be dealt with the same way as ".hash" sections in all respects; only the
dynamic linker cares about their contents.  To work with older dynamic
linkers (i.e.  preexisting releases of glibc), a binary must have the old
".hash" section.  The --hash-style=both option produces binaries that a new
dynamic linker can use more efficiently, but an old dynamic linker can
still handle.

The new section runs afoul of the custom linker scripts used to build vDSO
images for the kernel.  On ia64, the failure mode for this is a boot-time
panic because the vDSO's PT_IA_64_UNWIND segment winds up ill-formed.

This patch addresses the problem in two ways.

First, it mentions ".gnu.hash" in all the linker scripts alongside ".hash".
 This produces correct vDSO images with --hash-style=sysv (or old tools),
with --hash-style=gnu, or with --hash-style=both.

Second, it passes the --hash-style=sysv option when building the vDSO
images, so that ".gnu.hash" is not actually produced.  This is the most
conservative choice for compatibility with any old userland.  There is some
concern that some ancient glibc builds (though not any known old production
system) might choke on --hash-style=both binaries.  The optimizations
provided by the new style of hash section do not really matter for a DSO
with a tiny number of symbols, as the vDSO has.  If someone wants to use
=gnu or =both for their vDSO builds and worry less about that
compatibility, just change the option and the linker script changes will
make any choice work fine.

Signed-off-by: Roland McGrath <roland@redhat.com>
Cc: "Luck, Tony" <tony.luck@intel.com>
Cc: Kyle McMartin <kyle@mcmartin.ca>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Andi Kleen <ak@muc.de>
Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

15 files changed, 38 insertions, 4 deletions

diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt
index 14ef3868a32..0706699c9da 100644
--- a/Documentation/kbuild/makefiles.txt
+++ b/Documentation/kbuild/makefiles.txt
@@ -407,6 +407,20 @@ more details, with real examples.
 	The second argument is optional, and if supplied will be used
 	if first argument is not supported.
 
+    ld-option
+    	ld-option is used to check if $(CC) when used to link object files
+	supports the given option.  An optional second option may be
+	specified if first option are not supported.
+
+	Example:
+		#arch/i386/kernel/Makefile
+		vsyscall-flags += $(call ld-option, -Wl$(comma)--hash-style=sysv)
+
+	In the above example vsyscall-flags will be assigned the option
+	-Wl$(comma)--hash-style=sysv if it is supported by $(CC).
+	The second argument is optional, and if supplied will be used
+	if first argument is not supported.
+
     cc-option
 	cc-option is used to check if $(CC) support a given option, and not
 	supported to use an optional second option.
diff --git a/arch/i386/kernel/Makefile b/arch/i386/kernel/Makefile
index 1b452a1665c..ab98fc21a54 100644
--- a/arch/i386/kernel/Makefile
+++ b/arch/i386/kernel/Makefile
@@ -59,7 +59,8 @@ quiet_cmd_syscall = SYSCALL $@
 
 export CPPFLAGS_vsyscall.lds += -P -C -U$(ARCH)
 
-vsyscall-flags = -shared -s -Wl,-soname=linux-gate.so.1
+vsyscall-flags = -shared -s -Wl,-soname=linux-gate.so.1 \
+		 $(call ld-option, -Wl$(comma)--hash-style=sysv)
 SYSCFLAGS_vsyscall-sysenter.so	= $(vsyscall-flags)
 SYSCFLAGS_vsyscall-int80.so	= $(vsyscall-flags)
 
diff --git a/arch/i386/kernel/vsyscall.lds.S b/arch/i386/kernel/vsyscall.lds.S
index e26975fc68b..f66cd11adb7 100644
--- a/arch/i386/kernel/vsyscall.lds.S
+++ b/arch/i386/kernel/vsyscall.lds.S
@@ -10,6 +10,7 @@ SECTIONS
   . = VDSO_PRELINK + SIZEOF_HEADERS;
 
   .hash           : { *(.hash) }		:text
+  .gnu.hash       : { *(.gnu.hash) }
   .dynsym         : { *(.dynsym) }
   .dynstr         : { *(.dynstr) }
   .gnu.version    : { *(.gnu.version) }
diff --git a/arch/ia64/kernel/Makefile b/arch/ia64/kernel/Makefile
index 0e4553f320b..ad8215a3c58 100644
--- a/arch/ia64/kernel/Makefile
+++ b/arch/ia64/kernel/Makefile
@@ -45,7 +45,8 @@ CPPFLAGS_gate.lds := -P -C -U$(ARCH)
 quiet_cmd_gate = GATE $@
       cmd_gate = $(CC) -nostdlib $(GATECFLAGS_$(@F)) -Wl,-T,$(filter-out FORCE,$^) -o $@
 
-GATECFLAGS_gate.so = -shared -s -Wl,-soname=linux-gate.so.1
+GATECFLAGS_gate.so = -shared -s -Wl,-soname=linux-gate.so.1 \
+		     $(call ld-option, -Wl$(comma)--hash-style=sysv)
 $(obj)/gate.so: $(obj)/gate.lds $(obj)/gate.o FORCE
 	$(call if_changed,gate)
 
diff --git a/arch/ia64/kernel/gate.lds.S b/arch/ia64/kernel/gate.lds.S
index cc35cddfd4c..6d198339bf8 100644
--- a/arch/ia64/kernel/gate.lds.S
+++ b/arch/ia64/kernel/gate.lds.S
@@ -12,6 +12,7 @@ SECTIONS
   . = GATE_ADDR + SIZEOF_HEADERS;
 
   .hash				: { *(.hash) }				:readable
+  .gnu.hash			: { *(.gnu.hash) }
   .dynsym			: { *(.dynsym) }
   .dynstr			: { *(.dynstr) }
   .gnu.version			: { *(.gnu.version) }
diff --git a/arch/parisc/kernel/vmlinux.lds.S b/arch/parisc/kernel/vmlinux.lds.S
index 9989495a51d..b3677fc8eef 100644
--- a/arch/parisc/kernel/vmlinux.lds.S
+++ b/arch/parisc/kernel/vmlinux.lds.S
@@ -204,6 +204,7 @@ SECTIONS
 	*(.dynstr)
 	*(.dynamic)
 	*(.hash)
+	*(.gnu.hash)
 #endif
 	}
 
diff --git a/arch/powerpc/kernel/vdso32/Makefile b/arch/powerpc/kernel/vdso32/Makefile
index 8a3bed5f143..3726358faae 100644
--- a/arch/powerpc/kernel/vdso32/Makefile
+++ b/arch/powerpc/kernel/vdso32/Makefile
@@ -14,7 +14,8 @@ obj-vdso32 := $(addprefix $(obj)/, $(obj-vdso32))
 
 
 EXTRA_CFLAGS := -shared -s -fno-common -fno-builtin
-EXTRA_CFLAGS += -nostdlib -Wl,-soname=linux-vdso32.so.1
+EXTRA_CFLAGS += -nostdlib -Wl,-soname=linux-vdso32.so.1 \
+		$(call ld-option, -Wl$(comma)--hash-style=sysv)
 EXTRA_AFLAGS := -D__VDSO32__ -s
 
 obj-y += vdso32_wrapper.o
diff --git a/arch/powerpc/kernel/vdso32/vdso32.lds.S b/arch/powerpc/kernel/vdso32/vdso32.lds.S
index f4bad720cb0..6187af2d54c 100644
--- a/arch/powerpc/kernel/vdso32/vdso32.lds.S
+++ b/arch/powerpc/kernel/vdso32/vdso32.lds.S
@@ -14,6 +14,7 @@ SECTIONS
 {
   . = VDSO32_LBASE + SIZEOF_HEADERS;
   .hash           : { *(.hash) }			:text
+  .gnu.hash       : { *(.gnu.hash) }
   .dynsym         : { *(.dynsym) }
   .dynstr         : { *(.dynstr) }
   .gnu.version    : { *(.gnu.version) }
diff --git a/arch/powerpc/kernel/vdso64/Makefile b/arch/powerpc/kernel/vdso64/Makefile
index ab39988452c..43af9b2a6f3 100644
--- a/arch/powerpc/kernel/vdso64/Makefile
+++ b/arch/powerpc/kernel/vdso64/Makefile
@@ -8,7 +8,8 @@ targets := $(obj-vdso64) vdso64.so
 obj-vdso64 := $(addprefix $(obj)/, $(obj-vdso64))
 
 EXTRA_CFLAGS := -shared -s -fno-common -fno-builtin
-EXTRA_CFLAGS +=  -nostdlib -Wl,-soname=linux-vdso64.so.1
+EXTRA_CFLAGS += -nostdlib -Wl,-soname=linux-vdso64.so.1 \
+		$(call ld-option, -Wl$(comma)--hash-style=sysv)
 EXTRA_AFLAGS := -D__VDSO64__ -s
 
 obj-y += vdso64_wrapper.o
diff --git a/arch/powerpc/kernel/vdso64/vdso64.lds.S b/arch/powerpc/kernel/vdso64/vdso64.lds.S
index 4bdf224464a..4a2b6dc0960 100644
--- a/arch/powerpc/kernel/vdso64/vdso64.lds.S
+++ b/arch/powerpc/kernel/vdso64/vdso64.lds.S
@@ -12,6 +12,7 @@ SECTIONS
 {
   . = VDSO64_LBASE + SIZEOF_HEADERS;
   .hash           : { *(.hash) }		:text
+  .gnu.hash       : { *(.gnu.hash) }
   .dynsym         : { *(.dynsym) }
   .dynstr         : { *(.dynstr) }
   .gnu.version    : { *(.gnu.version) }
diff --git a/arch/ppc/kernel/vmlinux.lds.S b/arch/ppc/kernel/vmlinux.lds.S
index 09c6525cfa6..095fd332332 100644
--- a/arch/ppc/kernel/vmlinux.lds.S
+++ b/arch/ppc/kernel/vmlinux.lds.S
@@ -8,6 +8,7 @@ SECTIONS
   . = + SIZEOF_HEADERS;
   .interp : { *(.interp) }
   .hash          : { *(.hash)		}
+  .gnu.hash      : { *(.gnu.hash)	}
   .dynsym        : { *(.dynsym)		}
   .dynstr        : { *(.dynstr)		}
   .rel.text      : { *(.rel.text)		}
diff --git a/arch/um/kernel/dyn.lds.S b/arch/um/kernel/dyn.lds.S
index 2517ecb8bf2..68ed24df5c8 100644
--- a/arch/um/kernel/dyn.lds.S
+++ b/arch/um/kernel/dyn.lds.S
@@ -26,6 +26,7 @@ SECTIONS
 
   /* Read-only sections, merged into text segment: */
   .hash           : { *(.hash) }
+  .gnu.hash       : { *(.gnu.hash) }
   .dynsym         : { *(.dynsym) }
   .dynstr         : { *(.dynstr) }
   .gnu.version    : { *(.gnu.version) }
diff --git a/arch/x86_64/ia32/Makefile b/arch/x86_64/ia32/Makefile
index 62bc5f56da9..cdae36435e2 100644
--- a/arch/x86_64/ia32/Makefile
+++ b/arch/x86_64/ia32/Makefile
@@ -23,6 +23,7 @@ targets := $(foreach F,sysenter syscall,vsyscall-$F.o vsyscall-$F.so)
 # The DSO images are built using a special linker script
 quiet_cmd_syscall = SYSCALL $@
       cmd_syscall = $(CC) -m32 -nostdlib -shared -s \
+			  $(call ld-option, -Wl$(comma)--hash-style=sysv) \
 			   -Wl,-soname=linux-gate.so.1 -o $@ \
 			   -Wl,-T,$(filter-out FORCE,$^)
 
diff --git a/arch/x86_64/ia32/vsyscall.lds b/arch/x86_64/ia32/vsyscall.lds
index f2e75ed4c6c..1dc86ff5bcb 100644
--- a/arch/x86_64/ia32/vsyscall.lds
+++ b/arch/x86_64/ia32/vsyscall.lds
@@ -11,6 +11,7 @@ SECTIONS
   . = VSYSCALL_BASE + SIZEOF_HEADERS;
 
   .hash           : { *(.hash) }		:text
+  .gnu.hash       : { *(.gnu.hash) }
   .dynsym         : { *(.dynsym) }
   .dynstr         : { *(.dynstr) }
   .gnu.version    : { *(.gnu.version) }
diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 2180c88cfe8..f0113226353 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -85,6 +85,13 @@ cc-version = $(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-version.sh \
 cc-ifversion = $(shell if [ $(call cc-version, $(CC)) $(1) $(2) ]; then \
                        echo $(3); fi;)
 
+# ld-option
+# Usage: ldflags += $(call ld-option, -Wl$(comma)--hash-style=both)
+ld-option = $(shell if $(CC) $(1) \
+			     -nostdlib -o ldtest$$$$.out -xc /dev/null \
+             > /dev/null 2>&1; then echo "$(1)"; else echo "$(2)"; fi; \
+	     rm -f ldtest$$$$.out)
+
 ###
 # Shorthand for $(Q)$(MAKE) -f scripts/Makefile.build obj=
 # Usage: