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Re: [PATCH] Enable VDSO for static linking on s390

Hi Rafael,

sorry for the delay. I'm just returned from vacation.

Starting with your previous message, I saw the patch.
But if I look at "Re: [PATCH] Enable VDSO for static linking on s390" (https://www.sourceware.org/ml/libc-alpha/2018-12/msg00757.html) I can't see it.
Anyway on s390 the vdso is currently only mapped for dynamically linked elf binaries! See <kernel-src>/arch/s390/kernel/vdso.c: 
/*
 * This is called from binfmt_elf, we create the special vma for the
 * vDSO and insert it into the mm struct tree
 */
int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
{
	struct mm_struct *mm = current->mm;
	struct vm_area_struct *vma;
	unsigned long vdso_pages;
	unsigned long vdso_base;
	int rc;

	if (!vdso_enabled)
		return 0;
	/*
	 * Only map the vdso for dynamically linked elf binaries.
	 */
	if (!uses_interp)
		return 0;
...

What is your motivation to enable vdso for static binaries?
Do you have a special workload in mind?

Bye.
Stefan

On 12/26/2018 05:41 PM, Rafael Avila de Espindola wrote:

Hi Stefan,

Have you had a change to try the patch?

Thanks,
Rafael

"Rafael Avila de Espindola" <rafael@espindo.la> writes:


"Stefan Liebler" <stli@linux.ibm.com> writes:


Hi Rafael,

can you please resend the patch?


Attached.


But I have a question: Do I need a special kernel parameter / configuration?


I don't think so, but I don't know if there is something special on s390x.


When I run it on Intel, I recognize that there is a vdso mapped and
AT_SYSINFO_EHDR contains the address.


That was already working. What was missing is just glibc using the
loaded vdso.

What I have been using for testing is running the following program with
strace:

#include <time.h>
#include <stdio.h>
int main() {
     struct timespec ts;
     clock_gettime(CLOCK_REALTIME, &ts);
     printf("%ld.%09ld\n", ts.tv_sec, ts.tv_nsec);
     return 0;
}

My expectation is

* If built as shared, no syscall for clock_realtime.
* If built as static with glibc master, there will be a syscall.
* The patch avoids the syscall.

Cheers,
Rafael


 From ffe4dc79ffd5ffef09a1275208f56ec5686c74a1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Rafael=20=C3=81vila=20de=20Esp=C3=ADndola?=
  <rafael@espindo.la>
Date: Thu, 13 Dec 2018 19:25:34 -0800
Subject: [PATCH] Enable VDSO for static linking on s390

I don't have access to a s390, so I have not been able to test this.
---
  sysdeps/unix/sysv/linux/s390/init-first.c     | 8 +++-----
  sysdeps/unix/sysv/linux/s390/libc-vdso.h      | 3 ---
  sysdeps/unix/sysv/linux/s390/s390-32/sysdep.h | 3 +++
  sysdeps/unix/sysv/linux/s390/s390-64/sysdep.h | 3 +++
  4 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/sysdeps/unix/sysv/linux/s390/init-first.c b/sysdeps/unix/sysv/linux/s390/init-first.c
index 3a862309bf..10f47ef346 100644
--- a/sysdeps/unix/sysv/linux/s390/init-first.c
+++ b/sysdeps/unix/sysv/linux/s390/init-first.c
@@ -16,9 +16,8 @@
     License along with the GNU C Library; if not, see
     <http://www.gnu.org/licenses/>.  */
-#ifdef SHARED 
-# include <dl-vdso.h>
-# include <libc-vdso.h>
+#include <dl-vdso.h>
+#include <libc-vdso.h>
long int (*VDSO_SYMBOL(gettimeofday)) (struct timeval *, void *) 
     attribute_hidden;
@@ -54,7 +53,6 @@ _libc_vdso_platform_setup (void)
    VDSO_SYMBOL (getcpu) = p;
  }
-# define VDSO_SETUP _libc_vdso_platform_setup 
-#endif
+#define VDSO_SETUP _libc_vdso_platform_setup
#include <csu/init-first.c> 
diff --git a/sysdeps/unix/sysv/linux/s390/libc-vdso.h b/sysdeps/unix/sysv/linux/s390/libc-vdso.h
index 664bd15f3d..0d4ecb39a8 100644
--- a/sysdeps/unix/sysv/linux/s390/libc-vdso.h
+++ b/sysdeps/unix/sysv/linux/s390/libc-vdso.h
@@ -20,8 +20,6 @@
  #ifndef _LIBC_VDSO_H
  #define _LIBC_VDSO_H
-#ifdef SHARED 
-
  #include <sysdep-vdso.h>
extern long int (*VDSO_SYMBOL(gettimeofday)) (struct timeval *, void *) 
@@ -33,6 +31,5 @@ extern long int (*VDSO_SYMBOL(clock_getres)) (clockid_t, struct timespec *);
extern long int (*VDSO_SYMBOL(getcpu)) (unsigned *, unsigned *, void *) 
     attribute_hidden;
-#endif
#endif /* _LIBC_VDSO_H */ 
diff --git a/sysdeps/unix/sysv/linux/s390/s390-32/sysdep.h b/sysdeps/unix/sysv/linux/s390/s390-32/sysdep.h
index 0d683a5bcb..cebd4cbfad 100644
--- a/sysdeps/unix/sysv/linux/s390/s390-32/sysdep.h
+++ b/sysdeps/unix/sysv/linux/s390/s390-32/sysdep.h
@@ -19,6 +19,9 @@
  #ifndef _LINUX_S390_SYSDEP_H
  #define _LINUX_S390_SYSDEP_H
+/* Always enable vsyscalls on s390-32. */ 
+#define ALWAYS_USE_VSYSCALL 1
+
  #include <sysdeps/s390/s390-32/sysdep.h>
  #include <sysdeps/unix/sysdep.h>
  #include <sysdeps/unix/sysv/linux/sysdep.h>
diff --git a/sysdeps/unix/sysv/linux/s390/s390-64/sysdep.h b/sysdeps/unix/sysv/linux/s390/s390-64/sysdep.h
index 0414fc5f2c..348f1afb58 100644
--- a/sysdeps/unix/sysv/linux/s390/s390-64/sysdep.h
+++ b/sysdeps/unix/sysv/linux/s390/s390-64/sysdep.h
@@ -20,6 +20,9 @@
  #ifndef _LINUX_S390_SYSDEP_H
  #define _LINUX_S390_SYSDEP_H
+/* Always enable vsyscalls on s390-64. */ 
+#define ALWAYS_USE_VSYSCALL 1
+
  #include <sysdeps/s390/s390-64/sysdep.h>
  #include <sysdeps/unix/sysdep.h>
  #include <sysdeps/unix/sysv/linux/sysdep.h>
--
2.19.2
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