arm64: VDSO support

This patch adds VDSO support for 64-bit applications. The VDSO code is
currently used for sys_rt_sigreturn() and optimised gettimeofday()
(using the user-accessible generic counter).

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Olof Johansson <olof@lixom.net>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>

9 files changed, 781 insertions, 0 deletions

diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
new file mode 100644
index 000000000000..17948fc7d663
--- /dev/null
+++ b/arch/arm64/kernel/vdso.c
@@ -0,0 +1,261 @@
+/*
+ * VDSO implementation for AArch64 and vector page setup for AArch32.
+ *
+ * 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/kernel.h>
+#include <linux/clocksource.h>
+#include <linux/elf.h>
+#include <linux/err.h>
+#include <linux/errno.h>
+#include <linux/gfp.h>
+#include <linux/mm.h>
+#include <linux/sched.h>
+#include <linux/signal.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+
+#include <asm/cacheflush.h>
+#include <asm/signal32.h>
+#include <asm/vdso.h>
+#include <asm/vdso_datapage.h>
+
+extern char vdso_start, vdso_end;
+static unsigned long vdso_pages;
+static struct page **vdso_pagelist;
+
+/*
+ * The vDSO data page.
+ */
+static union {
+        struct vdso_data        data;
+        u8                      page[PAGE_SIZE];
+} vdso_data_store __page_aligned_data;
+struct vdso_data *vdso_data = &vdso_data_store.data;
+
+#ifdef CONFIG_COMPAT
+/*
+ * Create and map the vectors page for AArch32 tasks.
+ */
+static struct page *vectors_page[1];
+
+static int alloc_vectors_page(void)
+{
+        extern char __kuser_helper_start[], __kuser_helper_end[];
+        int kuser_sz = __kuser_helper_end - __kuser_helper_start;
+        unsigned long vpage;
+
+        vpage = get_zeroed_page(GFP_ATOMIC);
+
+        if (!vpage)
+                return -ENOMEM;
+
+        /* kuser helpers */
+        memcpy((void *)vpage + 0x1000 - kuser_sz, __kuser_helper_start,
+                kuser_sz);
+
+        /* sigreturn code */
+        memcpy((void *)vpage + AARCH32_KERN_SIGRET_CODE_OFFSET,
+                aarch32_sigret_code, sizeof(aarch32_sigret_code));
+
+        flush_icache_range(vpage, vpage + PAGE_SIZE);
+        vectors_page[0] = virt_to_page(vpage);
+
+        return 0;
+}
+arch_initcall(alloc_vectors_page);
+
+int aarch32_setup_vectors_page(struct linux_binprm *bprm, int uses_interp)
+{
+        struct mm_struct *mm = current->mm;
+        unsigned long addr = AARCH32_VECTORS_BASE;
+        int ret;
+
+        down_write(&mm->mmap_sem);
+        current->mm->context.vdso = (void *)addr;
+
+        /* Map vectors page at the high address. */
+        ret = install_special_mapping(mm, addr, PAGE_SIZE,
+                                      VM_READ|VM_EXEC|VM_MAYREAD|VM_MAYEXEC,
+                                      vectors_page);
+
+        up_write(&mm->mmap_sem);
+
+        return ret;
+}
+#endif /* CONFIG_COMPAT */
+
+static int __init vdso_init(void)
+{
+        struct page *pg;
+        char *vbase;
+        int i, ret = 0;
+
+        vdso_pages = (&vdso_end - &vdso_start) >> PAGE_SHIFT;
+        pr_info("vdso: %ld pages (%ld code, %ld data) at base %p\n",
+                vdso_pages + 1, vdso_pages, 1L, &vdso_start);
+
+        /* Allocate the vDSO pagelist, plus a page for the data. */
+        vdso_pagelist = kzalloc(sizeof(struct page *) * (vdso_pages + 1),
+                                GFP_KERNEL);
+        if (vdso_pagelist == NULL) {
+                pr_err("Failed to allocate vDSO pagelist!\n");
+                return -ENOMEM;
+        }
+
+        /* Grab the vDSO code pages. */
+        for (i = 0; i < vdso_pages; i++) {
+                pg = virt_to_page(&vdso_start + i*PAGE_SIZE);
+                ClearPageReserved(pg);
+                get_page(pg);
+                vdso_pagelist[i] = pg;
+        }
+
+        /* Sanity check the shared object header. */
+        vbase = vmap(vdso_pagelist, 1, 0, PAGE_KERNEL);
+        if (vbase == NULL) {
+                pr_err("Failed to map vDSO pagelist!\n");
+                return -ENOMEM;
+        } else if (memcmp(vbase, "\177ELF", 4)) {
+                pr_err("vDSO is not a valid ELF object!\n");
+                ret = -EINVAL;
+                goto unmap;
+        }
+
+        /* Grab the vDSO data page. */
+        pg = virt_to_page(vdso_data);
+        get_page(pg);
+        vdso_pagelist[i] = pg;
+
+unmap:
+        vunmap(vbase);
+        return ret;
+}
+arch_initcall(vdso_init);
+
+int arch_setup_additional_pages(struct linux_binprm *bprm,
+                                int uses_interp)
+{
+        struct mm_struct *mm = current->mm;
+        unsigned long vdso_base, vdso_mapping_len;
+        int ret;
+
+        /* Be sure to map the data page */
+        vdso_mapping_len = (vdso_pages + 1) << PAGE_SHIFT;
+
+        down_write(&mm->mmap_sem);
+        vdso_base = get_unmapped_area(NULL, 0, vdso_mapping_len, 0, 0);
+        if (IS_ERR_VALUE(vdso_base)) {
+                ret = vdso_base;
+                goto up_fail;
+        }
+        mm->context.vdso = (void *)vdso_base;
+
+        ret = install_special_mapping(mm, vdso_base, vdso_mapping_len,
+                                      VM_READ|VM_EXEC|
+                                      VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
+                                      vdso_pagelist);
+        if (ret) {
+                mm->context.vdso = NULL;
+                goto up_fail;
+        }
+
+up_fail:
+        up_write(&mm->mmap_sem);
+
+        return ret;
+}
+
+const char *arch_vma_name(struct vm_area_struct *vma)
+{
+        /*
+         * We can re-use the vdso pointer in mm_context_t for identifying
+         * the vectors page for compat applications. The vDSO will always
+         * sit above TASK_UNMAPPED_BASE and so we don't need to worry about
+         * it conflicting with the vectors base.
+         */
+        if (vma->vm_mm && vma->vm_start == (long)vma->vm_mm->context.vdso) {
+#ifdef CONFIG_COMPAT
+                if (vma->vm_start == AARCH32_VECTORS_BASE)
+                        return "[vectors]";
+#endif
+                return "[vdso]";
+        }
+
+        return NULL;
+}
+
+/*
+ * We define AT_SYSINFO_EHDR, so we need these function stubs to keep
+ * Linux happy.
+ */
+int in_gate_area_no_mm(unsigned long addr)
+{
+        return 0;
+}
+
+int in_gate_area(struct mm_struct *mm, unsigned long addr)
+{
+        return 0;
+}
+
+struct vm_area_struct *get_gate_vma(struct mm_struct *mm)
+{
+        return NULL;
+}
+
+/*
+ * Update the vDSO data page to keep in sync with kernel timekeeping.
+ */
+void update_vsyscall(struct timespec *ts, struct timespec *wtm,
+                     struct clocksource *clock, u32 mult)
+{
+        struct timespec xtime_coarse;
+        u32 use_syscall = strcmp(clock->name, "arch_sys_counter");
+
+        ++vdso_data->tb_seq_count;
+        smp_wmb();
+
+        xtime_coarse = __current_kernel_time();
+        vdso_data->use_syscall                  = use_syscall;
+        vdso_data->xtime_coarse_sec             = xtime_coarse.tv_sec;
+        vdso_data->xtime_coarse_nsec            = xtime_coarse.tv_nsec;
+
+        if (!use_syscall) {
+                vdso_data->cs_cycle_last        = clock->cycle_last;
+                vdso_data->xtime_clock_sec      = ts->tv_sec;
+                vdso_data->xtime_clock_nsec     = ts->tv_nsec;
+                vdso_data->cs_mult              = mult;
+                vdso_data->cs_shift             = clock->shift;
+                vdso_data->wtm_clock_sec        = wtm->tv_sec;
+                vdso_data->wtm_clock_nsec       = wtm->tv_nsec;
+        }
+
+        smp_wmb();
+        ++vdso_data->tb_seq_count;
+}
+
+void update_vsyscall_tz(void)
+{
+        ++vdso_data->tb_seq_count;
+        smp_wmb();
+        vdso_data->tz_minuteswest       = sys_tz.tz_minuteswest;
+        vdso_data->tz_dsttime           = sys_tz.tz_dsttime;
+        smp_wmb();
+        ++vdso_data->tb_seq_count;
+}
diff --git a/arch/arm64/kernel/vdso/.gitignore b/arch/arm64/kernel/vdso/.gitignore
new file mode 100644
index 000000000000..b8cc94e9698b
--- /dev/null
+++ b/arch/arm64/kernel/vdso/.gitignore
@@ -0,0 +1,2 @@
+vdso.lds
+vdso-offsets.h
diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
new file mode 100644
index 000000000000..d8064af42e62
--- /dev/null
+++ b/arch/arm64/kernel/vdso/Makefile
@@ -0,0 +1,63 @@
+#
+# Building a vDSO image for AArch64.
+#
+# Author: Will Deacon <will.deacon@arm.com>
+# Heavily based on the vDSO Makefiles for other archs.
+#
+
+obj-vdso := gettimeofday.o note.o sigreturn.o
+
+# Build rules
+targets := $(obj-vdso) vdso.so vdso.so.dbg
+obj-vdso := $(addprefix $(obj)/, $(obj-vdso))
+
+ccflags-y := -shared -fno-common -fno-builtin
+ccflags-y += -nostdlib -Wl,-soname=linux-vdso.so.1 \
+                $(call cc-ldoption, -Wl$(comma)--hash-style=sysv)
+
+obj-y += vdso.o
+extra-y += vdso.lds vdso-offsets.h
+CPPFLAGS_vdso.lds += -P -C -U$(ARCH)
+
+# Force dependency (incbin is bad)
+$(obj)/vdso.o : $(obj)/vdso.so
+
+# Link rule for the .so file, .lds has to be first
+$(obj)/vdso.so.dbg: $(src)/vdso.lds $(obj-vdso)
+        $(call if_changed,vdsold)
+
+# Strip rule for the .so file
+$(obj)/%.so: OBJCOPYFLAGS := -S
+$(obj)/%.so: $(obj)/%.so.dbg FORCE
+        $(call if_changed,objcopy)
+
+# Generate VDSO offsets using helper script
+gen-vdsosym := $(srctree)/$(src)/gen_vdso_offsets.sh
+quiet_cmd_vdsosym = VDSOSYM $@
+define cmd_vdsosym
+        $(NM) $< | $(gen-vdsosym) | LC_ALL=C sort > $@ && \
+        cp $@ include/generated/
+endef
+
+$(obj)/vdso-offsets.h: $(obj)/vdso.so.dbg FORCE
+        $(call if_changed,vdsosym)
+
+# Assembly rules for the .S files
+$(obj-vdso): %.o: %.S
+        $(call if_changed_dep,vdsoas)
+
+# Actual build commands
+quiet_cmd_vdsold = VDSOL $@
+      cmd_vdsold = $(CC) $(c_flags) -Wl,-T $^ -o $@
+quiet_cmd_vdsoas = VDSOA $@
+      cmd_vdsoas = $(CC) $(a_flags) -c -o $@ $<
+
+# Install commands for the unstripped file
+quiet_cmd_vdso_install = INSTALL $@
+      cmd_vdso_install = cp $(obj)/$@.dbg $(MODLIB)/vdso/$@
+
+vdso.so: $(obj)/vdso.so.dbg
+        @mkdir -p $(MODLIB)/vdso
+        $(call cmd,vdso_install)
+
+vdso_install: vdso.so
diff --git a/arch/arm64/kernel/vdso/gen_vdso_offsets.sh b/arch/arm64/kernel/vdso/gen_vdso_offsets.sh
new file mode 100755
index 000000000000..01924ff071ad
--- /dev/null
+++ b/arch/arm64/kernel/vdso/gen_vdso_offsets.sh
@@ -0,0 +1,15 @@
+#!/bin/sh
+
+#
+# Match symbols in the DSO that look like VDSO_*; produce a header file
+# of constant offsets into the shared object.
+#
+# Doing this inside the Makefile will break the $(filter-out) function,
+# causing Kbuild to rebuild the vdso-offsets header file every time.
+#
+# Author: Will Deacon <will.deacon@arm.com
+#
+
+LC_ALL=C
+sed -n -e 's/^00*/0/' -e \
+'s/^\([0-9a-fA-F]*\) . VDSO_\([a-zA-Z0-9_]*\)$/\#define vdso_offset_\2\t0x\1/p'
diff --git a/arch/arm64/kernel/vdso/gettimeofday.S b/arch/arm64/kernel/vdso/gettimeofday.S
new file mode 100644
index 000000000000..dcb8c203a3b2
--- /dev/null
+++ b/arch/arm64/kernel/vdso/gettimeofday.S
@@ -0,0 +1,242 @@
+/*
+ * Userspace implementations of gettimeofday() and friends.
+ *
+ * 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/linkage.h>
+#include <asm/asm-offsets.h>
+#include <asm/unistd.h>
+
+#define NSEC_PER_SEC_LO16       0xca00
+#define NSEC_PER_SEC_HI16       0x3b9a
+
+vdso_data       .req    x6
+use_syscall     .req    w7
+seqcnt          .req    w8
+
+        .macro  seqcnt_acquire
+9999:   ldr     seqcnt, [vdso_data, #VDSO_TB_SEQ_COUNT]
+        tbnz    seqcnt, #0, 9999b
+        dmb     ishld
+        ldr     use_syscall, [vdso_data, #VDSO_USE_SYSCALL]
+        .endm
+
+        .macro  seqcnt_read, cnt
+        dmb     ishld
+        ldr     \cnt, [vdso_data, #VDSO_TB_SEQ_COUNT]
+        .endm
+
+        .macro  seqcnt_check, cnt, fail
+        cmp     \cnt, seqcnt
+        b.ne    \fail
+        .endm
+
+        .text
+
+/* int __kernel_gettimeofday(struct timeval *tv, struct timezone *tz); */
+ENTRY(__kernel_gettimeofday)
+        .cfi_startproc
+        mov     x2, x30
+        .cfi_register x30, x2
+
+        /* Acquire the sequence counter and get the timespec. */
+        adr     vdso_data, _vdso_data
+1:      seqcnt_acquire
+        cbnz    use_syscall, 4f
+
+        /* If tv is NULL, skip to the timezone code. */
+        cbz     x0, 2f
+        bl      __do_get_tspec
+        seqcnt_check w13, 1b
+
+        /* Convert ns to us. */
+        mov     x11, #1000
+        udiv    x10, x10, x11
+        stp     x9, x10, [x0, #TVAL_TV_SEC]
+2:
+        /* If tz is NULL, return 0. */
+        cbz     x1, 3f
+        ldp     w4, w5, [vdso_data, #VDSO_TZ_MINWEST]
+        seqcnt_read w13
+        seqcnt_check w13, 1b
+        stp     w4, w5, [x1, #TZ_MINWEST]
+3:
+        mov     x0, xzr
+        ret     x2
+4:
+        /* Syscall fallback. */
+        mov     x8, #__NR_gettimeofday
+        svc     #0
+        ret     x2
+        .cfi_endproc
+ENDPROC(__kernel_gettimeofday)
+
+/* int __kernel_clock_gettime(clockid_t clock_id, struct timespec *tp); */
+ENTRY(__kernel_clock_gettime)
+        .cfi_startproc
+        cmp     w0, #CLOCK_REALTIME
+        ccmp    w0, #CLOCK_MONOTONIC, #0x4, ne
+        b.ne    2f
+
+        mov     x2, x30
+        .cfi_register x30, x2
+
+        /* Get kernel timespec. */
+        adr     vdso_data, _vdso_data
+1:      seqcnt_acquire
+        cbnz    use_syscall, 7f
+
+        bl      __do_get_tspec
+        seqcnt_check w13, 1b
+
+        cmp     w0, #CLOCK_MONOTONIC
+        b.ne    6f
+
+        /* Get wtm timespec. */
+        ldp     x14, x15, [vdso_data, #VDSO_WTM_CLK_SEC]
+
+        /* Check the sequence counter. */
+        seqcnt_read w13
+        seqcnt_check w13, 1b
+        b       4f
+2:
+        cmp     w0, #CLOCK_REALTIME_COARSE
+        ccmp    w0, #CLOCK_MONOTONIC_COARSE, #0x4, ne
+        b.ne    8f
+
+        /* Get coarse timespec. */
+        adr     vdso_data, _vdso_data
+3:      seqcnt_acquire
+        ldp     x9, x10, [vdso_data, #VDSO_XTIME_CRS_SEC]
+
+        cmp     w0, #CLOCK_MONOTONIC_COARSE
+        b.ne    6f
+
+        /* Get wtm timespec. */
+        ldp     x14, x15, [vdso_data, #VDSO_WTM_CLK_SEC]
+
+        /* Check the sequence counter. */
+        seqcnt_read w13
+        seqcnt_check w13, 3b
+4:
+        /* Add on wtm timespec. */
+        add     x9, x9, x14
+        add     x10, x10, x15
+
+        /* Normalise the new timespec. */
+        mov     x14, #NSEC_PER_SEC_LO16
+        movk    x14, #NSEC_PER_SEC_HI16, lsl #16
+        cmp     x10, x14
+        b.lt    5f
+        sub     x10, x10, x14
+        add     x9, x9, #1
+5:
+        cmp     x10, #0
+        b.ge    6f
+        add     x10, x10, x14
+        sub     x9, x9, #1
+
+6:      /* Store to the user timespec. */
+        stp     x9, x10, [x1, #TSPEC_TV_SEC]
+        mov     x0, xzr
+        ret     x2
+7:
+        mov     x30, x2
+8:      /* Syscall fallback. */
+        mov     x8, #__NR_clock_gettime
+        svc     #0
+        ret
+        .cfi_endproc
+ENDPROC(__kernel_clock_gettime)
+
+/* int __kernel_clock_getres(clockid_t clock_id, struct timespec *res); */
+ENTRY(__kernel_clock_getres)
+        .cfi_startproc
+        cbz     w1, 3f
+
+        cmp     w0, #CLOCK_REALTIME
+        ccmp    w0, #CLOCK_MONOTONIC, #0x4, ne
+        b.ne    1f
+
+        ldr     x2, 5f
+        b       2f
+1:
+        cmp     w0, #CLOCK_REALTIME_COARSE
+        ccmp    w0, #CLOCK_MONOTONIC_COARSE, #0x4, ne
+        b.ne    4f
+        ldr     x2, 6f
+2:
+        stp     xzr, x2, [x1]
+
+3:      /* res == NULL. */
+        mov     w0, wzr
+        ret
+
+4:      /* Syscall fallback. */
+        mov     x8, #__NR_clock_getres
+        svc     #0
+        ret
+5:
+        .quad   CLOCK_REALTIME_RES
+6:
+        .quad   CLOCK_COARSE_RES
+        .cfi_endproc
+ENDPROC(__kernel_clock_getres)
+
+/*
+ * Read the current time from the architected counter.
+ * Expects vdso_data to be initialised.
+ * Clobbers the temporary registers (x9 - x15).
+ * Returns:
+ *  - (x9, x10) = (ts->tv_sec, ts->tv_nsec)
+ *  - (x11, x12) = (xtime->tv_sec, xtime->tv_nsec)
+ *  - w13 = vDSO sequence counter
+ */
+ENTRY(__do_get_tspec)
+        .cfi_startproc
+
+        /* Read from the vDSO data page. */
+        ldr     x10, [vdso_data, #VDSO_CS_CYCLE_LAST]
+        ldp     x11, x12, [vdso_data, #VDSO_XTIME_CLK_SEC]
+        ldp     w14, w15, [vdso_data, #VDSO_CS_MULT]
+        seqcnt_read w13
+
+        /* Read the physical counter. */
+        isb
+        mrs     x9, cntpct_el0
+
+        /* Calculate cycle delta and convert to ns. */
+        sub     x10, x9, x10
+        /* We can only guarantee 56 bits of precision. */
+        movn    x9, #0xff0, lsl #48
+        and     x10, x9, x10
+        mul     x10, x10, x14
+        lsr     x10, x10, x15
+
+        /* Use the kernel time to calculate the new timespec. */
+        add     x10, x12, x10
+        mov     x14, #NSEC_PER_SEC_LO16
+        movk    x14, #NSEC_PER_SEC_HI16, lsl #16
+        udiv    x15, x10, x14
+        add     x9, x15, x11
+        mul     x14, x14, x15
+        sub     x10, x10, x14
+
+        ret
+        .cfi_endproc
+ENDPROC(__do_get_tspec)
diff --git a/arch/arm64/kernel/vdso/note.S b/arch/arm64/kernel/vdso/note.S
new file mode 100644
index 000000000000..b82c85e5d972
--- /dev/null
+++ b/arch/arm64/kernel/vdso/note.S
@@ -0,0 +1,28 @@
+/*
+ * 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>
+ *
+ * This supplies .note.* sections to go into the PT_NOTE inside the vDSO text.
+ * Here we can supply some information useful to userland.
+ */
+
+#include <linux/uts.h>
+#include <linux/version.h>
+#include <linux/elfnote.h>
+
+ELFNOTE_START(Linux, 0, "a")
+        .long LINUX_VERSION_CODE
+ELFNOTE_END
diff --git a/arch/arm64/kernel/vdso/sigreturn.S b/arch/arm64/kernel/vdso/sigreturn.S
new file mode 100644
index 000000000000..20d98effa7dd
--- /dev/null
+++ b/arch/arm64/kernel/vdso/sigreturn.S
@@ -0,0 +1,37 @@
+/*
+ * Sigreturn trampoline for returning from a signal when the SA_RESTORER
+ * flag is not set.
+ *
+ * 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/linkage.h>
+#include <asm/unistd.h>
+
+        .text
+
+        nop
+ENTRY(__kernel_rt_sigreturn)
+        .cfi_startproc
+        .cfi_signal_frame
+        .cfi_def_cfa    x29, 0
+        .cfi_offset     x29, 0 * 8
+        .cfi_offset     x30, 1 * 8
+        mov     x8, #__NR_rt_sigreturn
+        svc     #0
+        .cfi_endproc
+ENDPROC(__kernel_rt_sigreturn)
diff --git a/arch/arm64/kernel/vdso/vdso.S b/arch/arm64/kernel/vdso/vdso.S
new file mode 100644
index 000000000000..60c1db54b41a
--- /dev/null
+++ b/arch/arm64/kernel/vdso/vdso.S
@@ -0,0 +1,33 @@
+/*
+ * 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/arm64/kernel/vdso/vdso.so"
+        .balign PAGE_SIZE
+vdso_end:
+
+        .previous
diff --git a/arch/arm64/kernel/vdso/vdso.lds.S b/arch/arm64/kernel/vdso/vdso.lds.S
new file mode 100644
index 000000000000..8154b8d1c826
--- /dev/null
+++ b/arch/arm64/kernel/vdso/vdso.lds.S
@@ -0,0 +1,100 @@
+/*
+ * 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("elf64-littleaarch64", "elf64-bigaarch64", "elf64-littleaarch64")
+OUTPUT_ARCH(aarch64)
+
+SECTIONS
+{
+        . = VDSO_LBASE + 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
+
+        . = ALIGN(16);
+
+        .text           : { *(.text*) }                 :text   =0xd503201f
+        PROVIDE (__etext = .);
+        PROVIDE (_etext = .);
+        PROVIDE (etext = .);
+
+        .eh_frame_hdr   : { *(.eh_frame_hdr) }          :text   :eh_frame_hdr
+        .eh_frame       : { KEEP (*(.eh_frame)) }       :text
+
+        .dynamic        : { *(.dynamic) }               :text   :dynamic
+
+        .rodata         : { *(.rodata*) }               :text
+
+        _end = .;
+        PROVIDE(end = .);
+
+        . = ALIGN(PAGE_SIZE);
+        PROVIDE(_vdso_data = .);
+
+        /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;
+}
+
+/*
+ * This controls what symbols we export from the DSO.
+ */
+VERSION
+{
+        LINUX_2.6.39 {
+        global:
+                __kernel_rt_sigreturn;
+                __kernel_gettimeofday;
+                __kernel_clock_gettime;
+                __kernel_clock_getres;
+        local: *;
+        };
+}
+
+/*
+ * Make the sigreturn code visible to the kernel.
+ */
+VDSO_sigtramp           = __kernel_rt_sigreturn;