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ARM: 8330/1: add VDSO user-space code

Browse source 
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: Nathan Lynch <nathan_lynch@mentor.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Nathan Lynch 2015-03-25 19:14:22 +01:00 • committed by Russell King
commit 8512287a81
8 changed files with 700 additions and 0 deletions
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5
arch/arm/kernel/asm-offsets.c
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@ -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;
}

1
arch/arm/vdso/.gitignore vendored Normal file
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@ -0,0 +1 @@
vdso.lds

74
arch/arm/vdso/Makefile Normal file
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@ -0,0 +1,74 @@
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)

15
arch/arm/vdso/datapage.S Normal file
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@ -0,0 +1,15 @@
#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)

35
arch/arm/vdso/vdso.S Normal file
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@ -0,0 +1,35 @@
/*
* 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

87
arch/arm/vdso/vdso.lds.S Normal file
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@ -0,0 +1,87 @@
/*
* Adapted from arm64 version.
*
* GNU linker script for the VDSO library.
*
* 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>
* Heavily based on the vDSO linker scripts for other archs.
*/
#include <linux/const.h>
#include <asm/page.h>
#include <asm/vdso.h>
OUTPUT_FORMAT("elf32-littlearm", "elf32-bigarm", "elf32-littlearm")
OUTPUT_ARCH(arm)
SECTIONS
{
PROVIDE(_start = .);
. = SIZEOF_HEADERS;
.hash : { *(.hash) } :text
.gnu.hash : { *(.gnu.hash) }
.dynsym : { *(.dynsym) }
.dynstr : { *(.dynstr) }
.gnu.version : { *(.gnu.version) }
.gnu.version_d : { *(.gnu.version_d) }
.gnu.version_r : { *(.gnu.version_r) }
.note : { *(.note.*) } :text :note
.eh_frame_hdr : { *(.eh_frame_hdr) } :text :eh_frame_hdr
.eh_frame : { KEEP (*(.eh_frame)) } :text
.dynamic : { *(.dynamic) } :text :dynamic
.rodata : { *(.rodata*) } :text
.text : { *(.text*) } :text =0xe7f001f2
.got : { *(.got) }
.rel.plt : { *(.rel.plt) }
/DISCARD/ : {
*(.note.GNU-stack)
*(.data .data.* .gnu.linkonce.d.* .sdata*)
*(.bss .sbss .dynbss .dynsbss)
}
}
/*
* We must supply the ELF program headers explicitly to get just one
* PT_LOAD segment, and set the flags explicitly to make segments read-only.
*/
PHDRS
{
text PT_LOAD FLAGS(5) FILEHDR PHDRS; /* PF_R|PF_X */
dynamic PT_DYNAMIC FLAGS(4); /* PF_R */
note PT_NOTE FLAGS(4); /* PF_R */
eh_frame_hdr PT_GNU_EH_FRAME;
}
VERSION
{
LINUX_2.6 {
global:
__vdso_clock_gettime;
__vdso_gettimeofday;
local: *;
};
}

201
arch/arm/vdso/vdsomunge.c Normal file
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@ -0,0 +1,201 @@
/*
* Copyright 2015 Mentor Graphics Corporation.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; version 2 of the
* License.
*
* 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/>.
*
*
* vdsomunge - Host program which produces a shared object
* architecturally specified to be usable by both soft- and hard-float
* programs.
*
* The Procedure Call Standard for the ARM Architecture (ARM IHI
* 0042E) says:
*
* 6.4.1 VFP and Base Standard Compatibility
*
* Code compiled for the VFP calling standard is compatible with
* the base standard (and vice-versa) if no floating-point or
* containerized vector arguments or results are used.
*
* And ELF for the ARM Architecture (ARM IHI 0044E) (Table 4-2) says:
*
* If both EF_ARM_ABI_FLOAT_XXXX bits are clear, conformance to the
* base procedure-call standard is implied.
*
* The VDSO is built with -msoft-float, as with the rest of the ARM
* kernel, and uses no floating point arguments or results. The build
* process will produce a shared object that may or may not have the
* EF_ARM_ABI_FLOAT_SOFT flag set (it seems to depend on the binutils
* version; binutils starting with 2.24 appears to set it). The
* EF_ARM_ABI_FLOAT_HARD flag should definitely not be set, and this
* program will error out if it is.
*
* If the soft-float flag is set, this program clears it. That's all
* it does.
*/
#define _GNU_SOURCE
#include <byteswap.h>
#include <elf.h>
#include <errno.h>
#include <error.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
#define HOST_ORDER ELFDATA2LSB
#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
#define HOST_ORDER ELFDATA2MSB
#endif
/* Some of the ELF constants we'd like to use were added to <elf.h>
* relatively recently.
*/
#ifndef EF_ARM_EABI_VER5
#define EF_ARM_EABI_VER5 0x05000000
#endif
#ifndef EF_ARM_ABI_FLOAT_SOFT
#define EF_ARM_ABI_FLOAT_SOFT 0x200
#endif
#ifndef EF_ARM_ABI_FLOAT_HARD
#define EF_ARM_ABI_FLOAT_HARD 0x400
#endif
static const char *outfile;
static void cleanup(void)
{
if (error_message_count > 0 && outfile != NULL)
unlink(outfile);
}
static Elf32_Word read_elf_word(Elf32_Word word, bool swap)
{
return swap ? bswap_32(word) : word;
}
static Elf32_Half read_elf_half(Elf32_Half half, bool swap)
{
return swap ? bswap_16(half) : half;
}
static void write_elf_word(Elf32_Word val, Elf32_Word *dst, bool swap)
{
*dst = swap ? bswap_32(val) : val;
}
int main(int argc, char **argv)
{
const Elf32_Ehdr *inhdr;
bool clear_soft_float;
const char *infile;
Elf32_Word e_flags;
const void *inbuf;
struct stat stat;
void *outbuf;
bool swap;
int outfd;
int infd;
atexit(cleanup);
if (argc != 3)
error(EXIT_FAILURE, 0, "Usage: %s [infile] [outfile]", argv[0]);
infile = argv[1];
outfile = argv[2];
infd = open(infile, O_RDONLY);
if (infd < 0)
error(EXIT_FAILURE, errno, "Cannot open %s", infile);
if (fstat(infd, &stat) != 0)
error(EXIT_FAILURE, errno, "Failed stat for %s", infile);
inbuf = mmap(NULL, stat.st_size, PROT_READ, MAP_PRIVATE, infd, 0);
if (inbuf == MAP_FAILED)
error(EXIT_FAILURE, errno, "Failed to map %s", infile);
close(infd);
inhdr = inbuf;
if (memcmp(&inhdr->e_ident, ELFMAG, SELFMAG) != 0)
error(EXIT_FAILURE, 0, "Not an ELF file");
if (inhdr->e_ident[EI_CLASS] != ELFCLASS32)
error(EXIT_FAILURE, 0, "Unsupported ELF class");
swap = inhdr->e_ident[EI_DATA] != HOST_ORDER;
if (read_elf_half(inhdr->e_type, swap) != ET_DYN)
error(EXIT_FAILURE, 0, "Not a shared object");
if (read_elf_half(inhdr->e_machine, swap) != EM_ARM) {
error(EXIT_FAILURE, 0, "Unsupported architecture %#x",
inhdr->e_machine);
}
e_flags = read_elf_word(inhdr->e_flags, swap);
if (EF_ARM_EABI_VERSION(e_flags) != EF_ARM_EABI_VER5) {
error(EXIT_FAILURE, 0, "Unsupported EABI version %#x",
EF_ARM_EABI_VERSION(e_flags));
}
if (e_flags & EF_ARM_ABI_FLOAT_HARD)
error(EXIT_FAILURE, 0,
"Unexpected hard-float flag set in e_flags");
clear_soft_float = !!(e_flags & EF_ARM_ABI_FLOAT_SOFT);
outfd = open(outfile, O_RDWR | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR);
if (outfd < 0)
error(EXIT_FAILURE, errno, "Cannot open %s", outfile);
if (ftruncate(outfd, stat.st_size) != 0)
error(EXIT_FAILURE, errno, "Cannot truncate %s", outfile);
outbuf = mmap(NULL, stat.st_size, PROT_READ | PROT_WRITE, MAP_SHARED,
outfd, 0);
if (outbuf == MAP_FAILED)
error(EXIT_FAILURE, errno, "Failed to map %s", outfile);
close(outfd);
memcpy(outbuf, inbuf, stat.st_size);
if (clear_soft_float) {
Elf32_Ehdr *outhdr;
outhdr = outbuf;
e_flags &= ~EF_ARM_ABI_FLOAT_SOFT;
write_elf_word(e_flags, &outhdr->e_flags, swap);
}
if (msync(outbuf, stat.st_size, MS_SYNC) != 0)
error(EXIT_FAILURE, errno, "Failed to sync %s", outfile);
return EXIT_SUCCESS;
}

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arch/arm/vdso/vgettimeofday.c Normal file
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@ -0,0 +1,282 @@
/*
* Copyright 2015 Mentor Graphics Corporation.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; version 2 of the
* License.
*
* 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/>.
*/
#include <linux/compiler.h>
#include <linux/hrtimer.h>
#include <linux/time.h>
#include <asm/arch_timer.h>
#include <asm/barrier.h>
#include <asm/bug.h>
#include <asm/page.h>
#include <asm/unistd.h>
#include <asm/vdso_datapage.h>
#ifndef CONFIG_AEABI
#error This code depends on AEABI system call conventions
#endif
extern struct vdso_data *__get_datapage(void);
static notrace u32 __vdso_read_begin(const struct vdso_data *vdata)
{
u32 seq;
repeat:
seq = ACCESS_ONCE(vdata->seq_count);
if (seq & 1) {
cpu_relax();
goto repeat;
}
return seq;
}
static notrace u32 vdso_read_begin(const struct vdso_data *vdata)
{
u32 seq;
seq = __vdso_read_begin(vdata);
smp_rmb(); /* Pairs with smp_wmb in vdso_write_end */
return seq;
}
static notrace int vdso_read_retry(const struct vdso_data *vdata, u32 start)
{
smp_rmb(); /* Pairs with smp_wmb in vdso_write_begin */
return vdata->seq_count != start;
}
static notrace long clock_gettime_fallback(clockid_t _clkid,
struct timespec *_ts)
{
register struct timespec *ts asm("r1") = _ts;
register clockid_t clkid asm("r0") = _clkid;
register long ret asm ("r0");
register long nr asm("r7") = __NR_clock_gettime;
asm volatile(
" swi #0\n"
: "=r" (ret)
: "r" (clkid), "r" (ts), "r" (nr)
: "memory");
return ret;
}
static notrace int do_realtime_coarse(struct timespec *ts,
struct vdso_data *vdata)
{
u32 seq;
do {
seq = vdso_read_begin(vdata);
ts->tv_sec = vdata->xtime_coarse_sec;
ts->tv_nsec = vdata->xtime_coarse_nsec;
} while (vdso_read_retry(vdata, seq));
return 0;
}
static notrace int do_monotonic_coarse(struct timespec *ts,
struct vdso_data *vdata)
{
struct timespec tomono;
u32 seq;
do {
seq = vdso_read_begin(vdata);
ts->tv_sec = vdata->xtime_coarse_sec;
ts->tv_nsec = vdata->xtime_coarse_nsec;
tomono.tv_sec = vdata->wtm_clock_sec;
tomono.tv_nsec = vdata->wtm_clock_nsec;
} while (vdso_read_retry(vdata, seq));
ts->tv_sec += tomono.tv_sec;
timespec_add_ns(ts, tomono.tv_nsec);
return 0;
}
#ifdef CONFIG_ARM_ARCH_TIMER
static notrace u64 get_ns(struct vdso_data *vdata)
{
u64 cycle_delta;
u64 cycle_now;
u64 nsec;
cycle_now = arch_counter_get_cntvct();
cycle_delta = (cycle_now - vdata->cs_cycle_last) & vdata->cs_mask;
nsec = (cycle_delta * vdata->cs_mult) + vdata->xtime_clock_snsec;
nsec >>= vdata->cs_shift;
return nsec;
}
static notrace int do_realtime(struct timespec *ts, struct vdso_data *vdata)
{
u64 nsecs;
u32 seq;
do {
seq = vdso_read_begin(vdata);
if (!vdata->tk_is_cntvct)
return -1;
ts->tv_sec = vdata->xtime_clock_sec;
nsecs = get_ns(vdata);
} while (vdso_read_retry(vdata, seq));
ts->tv_nsec = 0;
timespec_add_ns(ts, nsecs);
return 0;
}
static notrace int do_monotonic(struct timespec *ts, struct vdso_data *vdata)
{
struct timespec tomono;
u64 nsecs;
u32 seq;
do {
seq = vdso_read_begin(vdata);
if (!vdata->tk_is_cntvct)
return -1;
ts->tv_sec = vdata->xtime_clock_sec;
nsecs = get_ns(vdata);
tomono.tv_sec = vdata->wtm_clock_sec;
tomono.tv_nsec = vdata->wtm_clock_nsec;
} while (vdso_read_retry(vdata, seq));
ts->tv_sec += tomono.tv_sec;
ts->tv_nsec = 0;
timespec_add_ns(ts, nsecs + tomono.tv_nsec);
return 0;
}
#else /* CONFIG_ARM_ARCH_TIMER */
static notrace int do_realtime(struct timespec *ts, struct vdso_data *vdata)
{
return -1;
}
static notrace int do_monotonic(struct timespec *ts, struct vdso_data *vdata)
{
return -1;
}
#endif /* CONFIG_ARM_ARCH_TIMER */
notrace int __vdso_clock_gettime(clockid_t clkid, struct timespec *ts)
{
struct vdso_data *vdata;
int ret = -1;
vdata = __get_datapage();
switch (clkid) {
case CLOCK_REALTIME_COARSE:
ret = do_realtime_coarse(ts, vdata);
break;
case CLOCK_MONOTONIC_COARSE:
ret = do_monotonic_coarse(ts, vdata);
break;
case CLOCK_REALTIME:
ret = do_realtime(ts, vdata);
break;
case CLOCK_MONOTONIC:
ret = do_monotonic(ts, vdata);
break;
default:
break;
}
if (ret)
ret = clock_gettime_fallback(clkid, ts);
return ret;
}
static notrace long gettimeofday_fallback(struct timeval *_tv,
struct timezone *_tz)
{
register struct timezone *tz asm("r1") = _tz;
register struct timeval *tv asm("r0") = _tv;
register long ret asm ("r0");
register long nr asm("r7") = __NR_gettimeofday;
asm volatile(
" swi #0\n"
: "=r" (ret)
: "r" (tv), "r" (tz), "r" (nr)
: "memory");
return ret;
}
notrace int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
{
struct timespec ts;
struct vdso_data *vdata;
int ret;
vdata = __get_datapage();
ret = do_realtime(&ts, vdata);
if (ret)
return gettimeofday_fallback(tv, tz);
if (tv) {
tv->tv_sec = ts.tv_sec;
tv->tv_usec = ts.tv_nsec / 1000;
}
if (tz) {
tz->tz_minuteswest = vdata->tz_minuteswest;
tz->tz_dsttime = vdata->tz_dsttime;
}
return ret;
}
/* Avoid unresolved references emitted by GCC */
void __aeabi_unwind_cpp_pr0(void)
{
}
void __aeabi_unwind_cpp_pr1(void)
{
}
void __aeabi_unwind_cpp_pr2(void)
{
}