[Qemu-devel] [PATCH 0/2] vdso for x86_64-linux-user

[Qemu-devel] [PATCH 0/2] vdso for x86_64-linux-user

[Richard Henderson]

This is a refresh of a patch I wrote in 2010, and have re-posted every
6 months thereafter.  To my knowledge, it has never been reviewed.

It supplies a replacement for the required x86-64 vdso.  Anyone trying
to emulate x86_64-linux on a host other than same will quickly run into
the lack of a gettimeofday syscall, which glibc assumes is always
provided by the vdso.


r~


Richard Henderson (2):
  linux-user: Build vdso for x64.
  linux-user: Load a VDSO for x86-64.

 Makefile                  |   3 +-
 linux-user/elfload.c      | 197 ++++++++++++++++++++++++++++++++++++++++++++--
 pc-bios/Makefile          |   5 ++
 pc-bios/vdso-linux-x64.S  | 100 +++++++++++++++++++++++
 pc-bios/vdso-linux-x64.ld |  79 +++++++++++++++++++
 pc-bios/vdso-linux-x64.so | Bin 0 -> 7419 bytes
 6 files changed, 376 insertions(+), 8 deletions(-)
 create mode 100644 pc-bios/vdso-linux-x64.S
 create mode 100644 pc-bios/vdso-linux-x64.ld
 create mode 100755 pc-bios/vdso-linux-x64.so

-- 
1.8.3.1

[Qemu-devel] [PATCH 1/2] linux-user: Build vdso for x64.

[Richard Henderson]

... Well, sortof.  The Makefile bits are broken.
Patch to load the vdso into the running program to follow.

Signed-off-by: Richard Henderson <rth@twiddle.net>
---
 Makefile                  |   3 +-
 pc-bios/Makefile          |   5 +++
 pc-bios/vdso-linux-x64.S  | 100 ++++++++++++++++++++++++++++++++++++++++++++++
 pc-bios/vdso-linux-x64.ld |  79 ++++++++++++++++++++++++++++++++++++
 pc-bios/vdso-linux-x64.so | Bin 0 -> 7419 bytes
 5 files changed, 186 insertions(+), 1 deletion(-)
 create mode 100644 pc-bios/vdso-linux-x64.S
 create mode 100644 pc-bios/vdso-linux-x64.ld
 create mode 100755 pc-bios/vdso-linux-x64.so

diff --git a/Makefile b/Makefile
index c06bfab..0148da1 100644
--- a/Makefile
+++ b/Makefile
@@ -296,7 +296,8 @@ multiboot.bin linuxboot.bin kvmvapic.bin \
 s390-zipl.rom \
 s390-ccw.img \
 spapr-rtas.bin slof.bin \
-palcode-clipper
+palcode-clipper \
+vdso-linux-x64.so
 else
 BLOBS=
 endif
diff --git a/pc-bios/Makefile b/pc-bios/Makefile
index 315288d..70e2485 100644
--- a/pc-bios/Makefile
+++ b/pc-bios/Makefile
@@ -15,5 +15,10 @@ all: $(TARGETS)
 %.dtb: %.dts
 	dtc -I dts -O dtb -o $@ $<
 
+vdso-linux-x64.so: vdso-linux-x64.o vdso-linux-x64.ld
+	$(CC) -nostdlib -shared -Wl,-T,vdso-linux-x64.ld \
+	  -Wl,-h,linux-vdso.so.1 -Wl,--hash-style=both \
+	  vdso-linux-x64.o -o $@
+
 clean:
 	rm -f $(TARGETS) *.o *~
diff --git a/pc-bios/vdso-linux-x64.S b/pc-bios/vdso-linux-x64.S
new file mode 100644
index 0000000..92efcd1
--- /dev/null
+++ b/pc-bios/vdso-linux-x64.S
@@ -0,0 +1,100 @@
+/*
+ *  x86-64 linux replacement vdso.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <asm/unistd.h>
+
+	.globl	__vdso_clock_gettime
+	.type	__vdso_clock_gettime, @function
+	.balign	16
+	.cfi_startproc
+__vdso_clock_gettime:
+	mov	$__NR_clock_gettime, %eax
+	syscall
+	ret
+	.cfi_endproc
+	.size	__vdso_clock_gettime, . - __vdso_clock_gettime
+
+clock_gettime = __vdso_clock_gettime
+	.weak	clock_gettime
+
+
+	.globl	__vdso_gettimeofday
+	.type	__vdso_gettimeofday, @function
+	.balign	16
+	.cfi_startproc
+__vdso_gettimeofday:
+	mov	$__NR_gettimeofday, %eax
+	syscall
+	ret
+	.cfi_endproc
+	.size	__vdso_gettimeofday, . - __vdso_gettimeofday
+
+gettimeofday = __vdso_gettimeofday
+	.weak	gettimeofday
+
+
+	.globl	__vdso_getcpu
+	.type	__vdso_getcpu, @function
+	.balign	16
+	.cfi_startproc
+__vdso_getcpu:
+	/* ??? There is no syscall number for this allocated on x64.
+	   We can handle this several ways:
+
+	   (1) Invent a syscall number for use within qemu.
+               It should be easy enough to pick a number that
+               is well out of the way of the kernel numbers.
+
+           (2) Force the emulated cpu to support the rdtscp insn,
+	       and initialize the TSC_AUX value the appropriate value.
+
+	   (3) Pretend that we're always running on cpu 0.
+
+	   This last is the one that's implemented here, with the
+	   tiny bit of extra code to support rdtscp in place.  */
+
+	xor	%ecx, %ecx		/* rdtscp w/ tsc_aux = 0 */
+
+	/* if (cpu != NULL) *cpu = (ecx & 0xfff); */
+	test	%rdi, %rdi
+	jz	1f
+	mov	%ecx, %eax
+	and	$0xfff, %eax
+	mov	%eax, (%rdi)
+
+	/* if (node != NULL) *node = (ecx >> 12); */
+1:	test	%rsi, %rsi
+	jz	2f
+	shr	$12, %ecx
+	mov	%ecx, (%rsi)
+
+2:	xor	%eax, %eax
+	ret
+	.cfi_endproc
+	.size	__vdso_getcpu, . - __vdso_getcpu
+
+getcpu = __vdso_getcpu
+	.weak	getcpu
+
+/* ??? Perhaps add elf notes.  E.g.
+
+   #include <linux/elfnote.h>
+   ELFNOTE_START(Linux, 0, "a")
+	.long LINUX_VERSION_CODE
+   ELFNOTE_END
+
+   but what version number would we set for QEMU?  */
diff --git a/pc-bios/vdso-linux-x64.ld b/pc-bios/vdso-linux-x64.ld
new file mode 100644
index 0000000..9e7e2d1
--- /dev/null
+++ b/pc-bios/vdso-linux-x64.ld
@@ -0,0 +1,79 @@
+/*
+ * Linker script for linux x64 replacement vdso.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+VERSION {
+	LINUX_2.6 {
+	global:
+		clock_gettime;
+		__vdso_clock_gettime;
+		gettimeofday;
+		__vdso_gettimeofday;
+		getcpu;
+		__vdso_getcpu;
+	local: *;
+	};
+}
+
+PHDRS {
+	phdr		PT_PHDR		FLAGS(4) PHDRS;
+	data		PT_LOAD		FLAGS(6) FILEHDR PHDRS;
+	text		PT_LOAD		FLAGS(5);
+	dynamic		PT_DYNAMIC	FLAGS(4);
+	note		PT_NOTE		FLAGS(4);
+	/* ??? Various versions of ld don't know PT_GNU_EH_FRAME. */
+	eh_frame_hdr	0x6474e550;
+}
+
+SECTIONS {
+	/* ??? We can't really prelink to any address without knowing
+	   something about the virtual memory space of the host, since
+	   that leaks over into the available memory space of the guest.  */
+	. = SIZEOF_HEADERS;
+
+	/* The following, including the FILEHDRS and PHDRS, are modified
+	   when we relocate the binary.  We want them to be initially
+	   writable for the relocation; we'll force them read-only after.  */
+	.dynamic	: { *(.dynamic) }	:data :dynamic
+	.dynsym		: { *(.dynsym) }	:data
+	.data		: {
+		/* There ought not be any real read-write data.
+		   But since we manipulated the segment layout,
+		   we have to put these sections somewhere.  */
+		*(.data*)
+		*(.sdata*)
+		*(.got.plt) *(.got)
+		*(.gnu.linkonce.d.*)
+		*(.bss*)
+		*(.dynbss*)
+		*(.gnu.linkonce.b.*)
+	}
+
+	. += 4096;
+	.hash		: { *(.hash) }		:text
+	.gnu.hash	: { *(.gnu.hash) }
+	.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	: { *(.eh_frame) }	:text
+	.rodata		: { *(.rodata) }
+
+	. = ALIGN(0x100);
+	.text		: { *(.text*) }		:text	=0x90909090
+}
diff --git a/pc-bios/vdso-linux-x64.so b/pc-bios/vdso-linux-x64.so
new file mode 100755
index 0000000000000000000000000000000000000000..5fd8221527f0fc54ce3f93e98e6b9e14dadc7489
GIT binary patch
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literal 0
HcmV?d00001

-- 
1.8.3.1

[Qemu-devel] [PATCH 2/2] linux-user: Load a VDSO for x86-64.

[Richard Henderson]

Signed-off-by: Richard Henderson <rth@twiddle.net>
---
 linux-user/elfload.c | 197 +++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 190 insertions(+), 7 deletions(-)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 7ce2eab..0ceae28 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -197,6 +197,8 @@ static void elf_core_copy_regs(target_elf_gregset_t *regs, const CPUX86State *en
     (*regs)[26] = env->segs[R_GS].selector & 0xffff;
 }
 
+#define VDSO_BASENAME  "vdso-linux-x64.so"
+
 #else
 
 #define ELF_START_MMAP 0x80000000
@@ -1029,6 +1031,10 @@ static inline void init_thread(struct target_pt_regs *regs, struct image_info *i
 #define ELF_HWCAP 0
 #endif
 
+#ifndef VDSO_BASENAME
+#define VDSO_BASENAME NULL
+#endif
+
 #ifdef TARGET_ABI32
 #undef ELF_CLASS
 #define ELF_CLASS ELFCLASS32
@@ -1332,7 +1338,8 @@ static abi_ulong loader_build_fdpic_loadmap(struct image_info *info, abi_ulong s
 static abi_ulong create_elf_tables(abi_ulong p, int argc, int envc,
                                    struct elfhdr *exec,
                                    struct image_info *info,
-                                   struct image_info *interp_info)
+                                   struct image_info *interp_info,
+                                   struct image_info *vdso_info)
 {
     abi_ulong sp;
     abi_ulong sp_auxv;
@@ -1388,16 +1395,21 @@ static abi_ulong create_elf_tables(abi_ulong p, int argc, int envc,
      */
     sp = sp &~ (abi_ulong)15;
     size = (DLINFO_ITEMS + 1) * 2;
-    if (k_platform)
+    if (k_platform) {
         size += 2;
+    }
+    if (vdso_info) {
+        size += 4;
+    }
 #ifdef DLINFO_ARCH_ITEMS
     size += DLINFO_ARCH_ITEMS * 2;
 #endif
     size += envc + argc + 2;
     size += 1;  /* argc itself */
     size *= n;
-    if (size & 15)
+    if (size & 15) {
         sp -= 16 - (size & 15);
+    }
 
     /* This is correct because Linux defines
      * elf_addr_t as Elf32_Off / Elf64_Off
@@ -1426,8 +1438,13 @@ static abi_ulong create_elf_tables(abi_ulong p, int argc, int envc,
     NEW_AUX_ENT(AT_CLKTCK, (abi_ulong) sysconf(_SC_CLK_TCK));
     NEW_AUX_ENT(AT_RANDOM, (abi_ulong) u_rand_bytes);
 
-    if (k_platform)
+    if (k_platform) {
         NEW_AUX_ENT(AT_PLATFORM, u_platform);
+    }
+    if (vdso_info) {
+        NEW_AUX_ENT(AT_SYSINFO, vdso_info->entry);
+        NEW_AUX_ENT(AT_SYSINFO_EHDR, vdso_info->load_addr);
+    }
 #ifdef ARCH_DLINFO
     /*
      * ARCH_DLINFO must come last so platform specific code can enforce
@@ -1843,6 +1860,165 @@ static void load_elf_interp(const char *filename, struct image_info *info,
     exit(-1);
 }
 
+static void load_elf_vdso(const char *basename, struct image_info *info,
+                          char bprm_buf[BPRM_BUF_SIZE])
+{
+    const char *errmsg;
+    char *filename;
+    int fd, retval, i;
+    abi_ulong load_bias;
+
+    /* ??? What we really need access to is qemu_find_file, but that is
+       only built for system targets at the moment.  */
+    filename = alloca(strlen(CONFIG_QEMU_DATADIR "/") + strlen(basename) + 1);
+    stpcpy(stpcpy(filename, CONFIG_QEMU_DATADIR "/"), basename);
+
+    fd = open(filename, O_RDONLY);
+    if (fd < 0) {
+        goto exit_perror;
+    }
+
+    retval = read(fd, bprm_buf, BPRM_BUF_SIZE);
+    if (retval < 0) {
+        goto exit_perror;
+    }
+    if (retval < BPRM_BUF_SIZE) {
+        memset(bprm_buf + retval, 0, BPRM_BUF_SIZE - retval);
+    }
+
+    load_elf_image(basename, fd, info, NULL, bprm_buf);
+    load_bias = info->load_bias;
+
+    /* We most likely need to relocate the VDSO image.  The one built into
+       the kernel is built for a fixed address.  The one built for QEMU is
+       not, since that requires close control of the guest address space.  */
+    if (load_bias) {
+        struct elfhdr *ehdr = (struct elfhdr *)bprm_buf;
+        struct elf_phdr *phdr;
+        abi_ulong dynamic_addr = -1;
+        abi_ulong dynsym_addr = -1;
+
+        /* ??? Assume QEMU's VDSO is built "properly", which arranges
+           for the PHDRs, and all the sections manipulated below, to
+           be included with a writable load segment.  */
+
+        /* ??? One might think that we'd need to relocate ehdr.e_entry,
+           but for some reason glibc does that one itself, though that
+           is also available via the AT_SYSINFO entry.  */
+
+        /* Relocate the program headers.  */
+        phdr = (struct elf_phdr *)g2h(info->load_addr + ehdr->e_phoff);
+        bswap_phdr(phdr, ehdr->e_phnum);
+        for (i = 0; i < ehdr->e_phnum; ++i) {
+            phdr[i].p_vaddr += load_bias;
+            phdr[i].p_paddr += load_bias;
+            if (phdr[i].p_type == PT_DYNAMIC) {
+                dynamic_addr = phdr[i].p_vaddr;
+            }
+        }
+        bswap_phdr(phdr, ehdr->e_phnum);
+
+        /* Relocate the DYNAMIC entries.  */
+        if (dynamic_addr != -1) {
+            abi_ulong tag, val, *dyn = (abi_ulong *)g2h(dynamic_addr);
+            do {
+                tag = tswapl(dyn[0]);
+                val = tswapl(dyn[1]);
+                switch (tag) {
+                case DT_SYMTAB:
+                    dynsym_addr = load_bias + val;
+                    dyn[1] = tswapl(dynsym_addr);
+                    break;
+                case DT_SYMENT:
+                    if (val != sizeof(struct elf_sym)) {
+                        errmsg = "VDSO has an unexpected dynamic symbol size";
+                        goto exit_errmsg;
+                    }
+                    break;
+
+                case DT_HASH:
+                case DT_STRTAB:
+                case DT_VERDEF:
+                case DT_VERSYM:
+                case DT_ADDRRNGLO ... DT_ADDRRNGHI:
+                    /* These entries store an address in the entry.  */
+                    dyn[1] = tswapl(load_bias + val);
+                    break;
+
+                case DT_NULL:
+                case DT_STRSZ:
+                case DT_SONAME:
+                case DT_DEBUG:
+                case DT_FLAGS:
+                case DT_FLAGS_1:
+                case DT_VERDEFNUM:
+                case DT_VALRNGLO ... DT_VALRNGHI:
+                    /* These entries store an integer in the entry.  */
+                    break;
+
+                case DT_REL:
+                case DT_RELA:
+                    /* These entries indicate that the VDSO was built
+                       incorrectly.  It should not have real relocations.  */
+                    errmsg = "VDSO has relocations";
+                    goto exit_errmsg;
+                case DT_NEEDED:
+                case DT_VERNEED:
+                    errmsg = "VDSO has external dependancies";
+                    goto exit_errmsg;
+
+                default:
+                    /* This is probably something target specific.  */
+                    errmsg = "VDSO has unknown DYNAMIC entry";
+                    goto exit_errmsg;
+                }
+                dyn += 2;
+            } while (tag != DT_NULL);
+        }
+
+        /* Relocate the dynamic symbol table.  */
+        if (dynsym_addr != -1) {
+            struct elf_shdr *shdr;
+            struct elf_sym *sym;
+            int dynsym_size = 0;
+
+            /* Read the section headers to find out the size of the
+               dynamic symbol table.  */
+            shdr = (struct elf_shdr *)g2h(info->load_addr + ehdr->e_shoff);
+            for (i = 0; i < ehdr->e_shnum; ++i) {
+                abi_ulong addr = tswapl(shdr[i].sh_addr) + load_bias;
+                if (addr == dynsym_addr) {
+                    dynsym_size = tswapl(shdr[i].sh_size);
+                    break;
+                }
+            }
+
+            sym = (struct elf_sym *)g2h(dynsym_addr);
+            for (i = 0; i < dynsym_size / sizeof(*sym); ++i) {
+                sym[i].st_value = tswapl(tswapl(sym[i].st_value) + load_bias);
+            }
+        }
+    }
+
+    /* Mark the VDSO writable segment read-only.  */
+    /* ??? This assumes that the VDSO implementation doesn't actually
+       have any truely writable data.  Perhaps we should instead use
+       the PT_GNU_RELRO header to indicate that we really want this.  */
+    retval = target_mprotect(info->start_data, info->brk - info->start_data,
+                             PROT_READ);
+    if (retval < 0) {
+        goto exit_perror;
+    }
+    return;
+
+ exit_perror:
+    errmsg = strerror(errno);
+ exit_errmsg:
+    fprintf(stderr, "%s: %s\n", filename, errmsg);
+    exit(-1);
+}
+
+
 static int symfind(const void *s0, const void *s1)
 {
     target_ulong addr = *(target_ulong *)s0;
@@ -1990,7 +2166,7 @@ give_up:
 int load_elf_binary(struct linux_binprm * bprm, struct target_pt_regs * regs,
                     struct image_info * info)
 {
-    struct image_info interp_info;
+    struct image_info interp_info, vdso_info;
     struct elfhdr elf_ex;
     char *elf_interpreter = NULL;
 
@@ -2037,8 +2213,15 @@ int load_elf_binary(struct linux_binprm * bprm, struct target_pt_regs * regs,
         }
     }
 
-    bprm->p = create_elf_tables(bprm->p, bprm->argc, bprm->envc, &elf_ex,
-                                info, (elf_interpreter ? &interp_info : NULL));
+    /* If we've been given a VDSO to load, do so.  */
+    if (VDSO_BASENAME) {
+        load_elf_vdso(VDSO_BASENAME, &vdso_info, bprm->buf);
+    }
+
+    bprm->p = create_elf_tables(bprm->p, bprm->argc, bprm->envc,
+                                &elf_ex, info,
+                                (elf_interpreter ? &interp_info : NULL),
+                                (VDSO_BASENAME ? &vdso_info : NULL));
     info->start_stack = bprm->p;
 
     /* If we have an interpreter, set that as the program's entry point.
-- 
1.8.3.1

Re: [Qemu-devel] [PATCH 0/2] vdso for x86_64-linux-user

[Peter Maydell]

On 23 July 2013 21:27, Richard Henderson <rth@twiddle.net> wrote:
> This is a refresh of a patch I wrote in 2010, and have re-posted every
> 6 months thereafter.  To my knowledge, it has never been reviewed.
>
> It supplies a replacement for the required x86-64 vdso.  Anyone trying
> to emulate x86_64-linux on a host other than same will quickly run into
> the lack of a gettimeofday syscall, which glibc assumes is always
> provided by the vdso.

Do we really need to mess with building an x86 shared object
and pulling it in, rather than the kind of ad-hoc way we
handle the ARM commpage?

-- PMM

Re: [Qemu-devel] [PATCH 0/2] vdso for x86_64-linux-user

[Richard Henderson]

On 07/23/2013 11:15 AM, Peter Maydell wrote:
> On 23 July 2013 21:27, Richard Henderson <rth@twiddle.net> wrote:
>> This is a refresh of a patch I wrote in 2010, and have re-posted every
>> 6 months thereafter.  To my knowledge, it has never been reviewed.
>>
>> It supplies a replacement for the required x86-64 vdso.  Anyone trying
>> to emulate x86_64-linux on a host other than same will quickly run into
>> the lack of a gettimeofday syscall, which glibc assumes is always
>> provided by the vdso.
> 
> Do we really need to mess with building an x86 shared object
> and pulling it in, rather than the kind of ad-hoc way we
> handle the ARM commpage?

Isn't the arm ad-hoc really the much larger and uglier hack?


r~

Re: [Qemu-devel] [PATCH 0/2] vdso for x86_64-linux-user

[Peter Maydell]

On 24 July 2013 17:34, Richard Henderson <rth@twiddle.net> wrote:
> On 07/23/2013 11:15 AM, Peter Maydell wrote:
>> On 23 July 2013 21:27, Richard Henderson <rth@twiddle.net> wrote:
>>> This is a refresh of a patch I wrote in 2010, and have re-posted every
>>> 6 months thereafter.  To my knowledge, it has never been reviewed.
>>>
>>> It supplies a replacement for the required x86-64 vdso.  Anyone trying
>>> to emulate x86_64-linux on a host other than same will quickly run into
>>> the lack of a gettimeofday syscall, which glibc assumes is always
>>> provided by the vdso.
>>
>> Do we really need to mess with building an x86 shared object
>> and pulling it in, rather than the kind of ad-hoc way we
>> handle the ARM commpage?
>
> Isn't the arm ad-hoc really the much larger and uglier hack?

Maaaybe, but it doesn't require a cross-compiler :-)

-- PMM

Re: [Qemu-devel] [PATCH 0/2] vdso for x86_64-linux-user

[Richard Henderson]

On 07/24/2013 06:39 AM, Peter Maydell wrote:
> On 24 July 2013 17:34, Richard Henderson <rth@twiddle.net> wrote:
>> On 07/23/2013 11:15 AM, Peter Maydell wrote:
>>> On 23 July 2013 21:27, Richard Henderson <rth@twiddle.net> wrote:
>>>> This is a refresh of a patch I wrote in 2010, and have re-posted every
>>>> 6 months thereafter.  To my knowledge, it has never been reviewed.
>>>>
>>>> It supplies a replacement for the required x86-64 vdso.  Anyone trying
>>>> to emulate x86_64-linux on a host other than same will quickly run into
>>>> the lack of a gettimeofday syscall, which glibc assumes is always
>>>> provided by the vdso.
>>>
>>> Do we really need to mess with building an x86 shared object
>>> and pulling it in, rather than the kind of ad-hoc way we
>>> handle the ARM commpage?
>>
>> Isn't the arm ad-hoc really the much larger and uglier hack?
> 
> Maaaybe, but it doesn't require a cross-compiler :-)

The 7k binary is checked in to the repository, so a cross-compiler
(or host compiler for x86_64, which is easier to come by) would
only be needed when the source changes.  ;-)


r~