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Commit 8512287a authored by Nathan Lynch's avatar Nathan Lynch Committed by Russell King
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ARM: 8330/1: add VDSO user-space code 



Place VDSO-related user-space code in arch/arm/kernel/vdso/.

It is almost completely written in C with some assembly helpers to
load the data page address, sample the counter, and fall back to
system calls when necessary.

The VDSO can service gettimeofday and clock_gettime when
CONFIG_ARM_ARCH_TIMER is enabled and the architected timer is present
(and correctly configured).  It reads the CP15-based virtual counter
to compute high-resolution timestamps.

Of particular note is that a post-processing step ("vdsomunge") is
necessary to produce a shared object which is architecturally allowed
to be used by both soft- and hard-float EABI programs.

The 2012 edition of the ARM ABI defines Tag_ABI_VFP_args = 3 "Code is
compatible with both the base and VFP variants; the user did not
permit non-variadic functions to pass FP parameters/results."
Unfortunately current toolchains do not support this tag, which is
ideally what we would use.

The best available option is to ensure that both EF_ARM_ABI_FLOAT_SOFT
and EF_ARM_ABI_FLOAT_HARD are unset in the ELF header's e_flags,
indicating that the shared object is "old" and should be accepted for
backward compatibility's sake.  While binutils < 2.24 appear to
produce a vdso.so with both flags clear, 2.24 always sets
EF_ARM_ABI_FLOAT_SOFT, with no way to inhibit this behavior.  So we
have to fix things up with a custom post-processing step.

In fact, the VDSO code in glibc does much less validation (including
checking these flags) than the code for handling conventional
file-backed shared libraries, so this is a bit moot unless glibc's
VDSO code becomes more strict.

Signed-off-by: default avatarNathan Lynch <nathan_lynch@mentor.com>
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
parent 1713ce7c

arch/arm/kernel/asm-offsets.c

+5 −0
Original line number Diff line number Diff line
@@ -25,6 +25,7 @@ 
#include <asm/memory.h>

#include <asm/procinfo.h>

#include <asm/suspend.h>

#include <asm/vdso_datapage.h>

#include <asm/hardware/cache-l2x0.h>

#include <linux/kbuild.h>
@@ -209,6 +210,10 @@ int main(void) 
  DEFINE(KVM_VGIC_VCTRL,	offsetof(struct kvm, arch.vgic.vctrl_base));

#endif

  DEFINE(KVM_VTTBR,		offsetof(struct kvm, arch.vttbr));

#endif

  BLANK();

#ifdef CONFIG_VDSO

  DEFINE(VDSO_DATA_SIZE,	sizeof(union vdso_data_store));

#endif

  return 0; 

}

arch/arm/vdso/.gitignore

0 → 100644
+1 −0
Original line number Diff line number Diff line 
vdso.lds

arch/arm/vdso/Makefile

0 → 100644
+74 −0
Original line number Diff line number Diff line 
hostprogs-y := vdsomunge



obj-vdso := vgettimeofday.o datapage.o



# Build rules

targets := $(obj-vdso) vdso.so vdso.so.dbg vdso.so.raw vdso.lds

obj-vdso := $(addprefix $(obj)/, $(obj-vdso))



ccflags-y := -shared -fPIC -fno-common -fno-builtin -fno-stack-protector

ccflags-y += -nostdlib -Wl,-soname=linux-vdso.so.1 -DDISABLE_BRANCH_PROFILING

ccflags-y += -Wl,--no-undefined $(call cc-ldoption, -Wl$(comma)--hash-style=sysv)



obj-y += vdso.o

extra-y += vdso.lds

CPPFLAGS_vdso.lds += -P -C -U$(ARCH)



CFLAGS_REMOVE_vdso.o = -pg



# Force -O2 to avoid libgcc dependencies

CFLAGS_REMOVE_vgettimeofday.o = -pg -Os

CFLAGS_vgettimeofday.o = -O2



# Disable gcov profiling for VDSO code

GCOV_PROFILE := n



# Force dependency

$(obj)/vdso.o : $(obj)/vdso.so



# Link rule for the .so file

$(obj)/vdso.so.raw: $(src)/vdso.lds $(obj-vdso) FORCE

	$(call if_changed,vdsold)



$(obj)/vdso.so.dbg: $(obj)/vdso.so.raw $(obj)/vdsomunge FORCE

	$(call if_changed,vdsomunge)



# Strip rule for the .so file

$(obj)/%.so: OBJCOPYFLAGS := -S

$(obj)/%.so: $(obj)/%.so.dbg FORCE

	$(call if_changed,objcopy)



# Actual build commands

quiet_cmd_vdsold = VDSO    $@

      cmd_vdsold = $(CC) $(c_flags) -Wl,-T $(filter %.lds,$^) $(filter %.o,$^) \

                   $(call cc-ldoption, -Wl$(comma)--build-id) \

                   -Wl,-Bsymbolic -Wl,-z,max-page-size=4096 \

                   -Wl,-z,common-page-size=4096 -o $@



quiet_cmd_vdsomunge = MUNGE   $@

      cmd_vdsomunge = $(objtree)/$(obj)/vdsomunge $< $@



#

# Install the unstripped copy of vdso.so.dbg.  If our toolchain

# supports build-id, install .build-id links as well.

#

# Cribbed from arch/x86/vdso/Makefile.

#

quiet_cmd_vdso_install = INSTALL $<

define cmd_vdso_install

	cp $< "$(MODLIB)/vdso/vdso.so"; \

	if readelf -n $< | grep -q 'Build ID'; then \

	  buildid=`readelf -n $< |grep 'Build ID' |sed -e 's/^.*Build ID: \(.*\)$$/\1/'`; \

	  first=`echo $$buildid | cut -b-2`; \

	  last=`echo $$buildid | cut -b3-`; \

	  mkdir -p "$(MODLIB)/vdso/.build-id/$$first"; \

	  ln -sf "../../vdso.so" "$(MODLIB)/vdso/.build-id/$$first/$$last.debug"; \

	fi

endef



$(MODLIB)/vdso: FORCE

	@mkdir -p $(MODLIB)/vdso



PHONY += vdso_install

vdso_install: $(obj)/vdso.so.dbg $(MODLIB)/vdso FORCE

	$(call cmd,vdso_install)

arch/arm/vdso/datapage.S

0 → 100644
+15 −0
Original line number Diff line number Diff line 
#include <linux/linkage.h>

#include <asm/asm-offsets.h>



	.align 2

.L_vdso_data_ptr:

	.long	_start - . - VDSO_DATA_SIZE



ENTRY(__get_datapage)

	.fnstart

	adr	r0, .L_vdso_data_ptr

	ldr	r1, [r0]

	add	r0, r0, r1

	bx	lr

	.fnend

ENDPROC(__get_datapage)

arch/arm/vdso/vdso.S

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+35 −0
Original line number Diff line number Diff line 
/*

 * Adapted from arm64 version.

 *

 * Copyright (C) 2012 ARM Limited

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 as

 * published by the Free Software Foundation.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program.  If not, see <http://www.gnu.org/licenses/>.

 *

 * Author: Will Deacon <will.deacon@arm.com>

 */



#include <linux/init.h>

#include <linux/linkage.h>

#include <linux/const.h>

#include <asm/page.h>



	__PAGE_ALIGNED_DATA



	.globl vdso_start, vdso_end

	.balign PAGE_SIZE

vdso_start:

	.incbin "arch/arm/vdso/vdso.so"

	.balign PAGE_SIZE

vdso_end:



	.previous