[03/12] s390: Enable VDSO for static linking
Commit Message
On 8/2/19 2:34 PM, Adhemerval Zanella wrote:
> Ping.
>
> On 14/06/2019 12:28, Adhemerval Zanella wrote:
>> Although s390 explicit does not enable vDSO for binaries without
>> (arch/s390/kernel/vdso.c:217), there is no indication in the code
>> the rationale for disabling it. In fact, I rebuilt a kernel with the
>> check removed and the vDSO does work for static build for supplied
>> symbols.
Hi Adhemerval,
Sorry, I haven't recognized this patch as it was hidden behind the
email-thread starting with "[PATCH 01/12] m68k: Remove vDSO support".
Please cc me if I'm not responding for s390 patches.
I've just had a look into the kernel arch/s390/kernel/vdso.c file
and I'm a little bit confused regarding the line number 217 (see my
excerpt below).
Just to be sure, have you removed the "if (!uses_interp)" or the "if
(!vdso_enabled)"?
/*
* 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;
217: if (!vdso_enabled)
return 0;
/*
* Only map the vdso for dynamically linked elf binaries.
*/
222: if (!uses_interp)
return 0;
As far as I know, vdso was disabled for statically linked binaries as
glibc had not supported it and thus nothing "useless" was mapped
(especially on 31bit).
I've also cc'ed Heiko. Perhaps he can also enable it on s390 for
statically linked binaries.
Nevertheless this patch breaks s390. I've just committed the attached
fix which adds the removed VDSO_SETUP macro definition.
Bye.
Stefan
Comments
On 06/08/2019 11:08, Stefan Liebler wrote:
> On 8/2/19 2:34 PM, Adhemerval Zanella wrote:
>> Ping.
>>
>> On 14/06/2019 12:28, Adhemerval Zanella wrote:
>>> Although s390 explicit does not enable vDSO for binaries without
>>> (arch/s390/kernel/vdso.c:217), there is no indication in the code
>>> the rationale for disabling it. In fact, I rebuilt a kernel with the
>>> check removed and the vDSO does work for static build for supplied
>>> symbols.
>
> Hi Adhemerval,
>
> Sorry, I haven't recognized this patch as it was hidden behind the email-thread starting with "[PATCH 01/12] m68k: Remove vDSO support". Please cc me if I'm not responding for s390 patches.
>
> I've just had a look into the kernel arch/s390/kernel/vdso.c file
> and I'm a little bit confused regarding the line number 217 (see my excerpt below).
> Just to be sure, have you removed the "if (!uses_interp)" or the "if (!vdso_enabled)"?
>
> /*
> * 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;
>
> 217: if (!vdso_enabled)
> return 0;
> /*
> * Only map the vdso for dynamically linked elf binaries.
> */
> 222: if (!uses_interp)
> return 0;
In fact it was the !uses_interp that I commented out to enable the vDSO page on
the system emulated environment I used.
>
>
> As far as I know, vdso was disabled for statically linked binaries as glibc had not supported it and thus nothing "useless" was mapped (especially on 31bit).
> I've also cc'ed Heiko. Perhaps he can also enable it on s390 for statically linked binaries.
Yeah, I noted that s390 is an outlier here where all the other architectures do
map the vDSO even for statically linked binaries. Thanks for checking on it.
>
> Nevertheless this patch breaks s390. I've just committed the attached fix which adds the removed VDSO_SETUP macro definition.
Sigh, this line was removed with a cherry-pick, sorry about that.
On Tue, Aug 06, 2019 at 04:08:02PM +0200, Stefan Liebler wrote:
> 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;
>
> 217: if (!vdso_enabled)
> return 0;
> /*
> * Only map the vdso for dynamically linked elf binaries.
> */
> 222: if (!uses_interp)
> return 0;
>
>
> As far as I know, vdso was disabled for statically linked binaries as glibc
> had not supported it and thus nothing "useless" was mapped (especially on
> 31bit).
> I've also cc'ed Heiko. Perhaps he can also enable it on s390 for statically
> linked binaries.
That was introduced in the kernel with
commit fc5243d98ac2575ad14a974b3c097e9ba874c03d
Author: Martin Schwidefsky <schwidefsky@de.ibm.com>
Date: Thu Dec 25 13:38:35 2008 +0100
[S390] arch_setup_additional_pages arguments
arch_setup_additional_pages currently gets two arguments, the binary
format descripton and an indication if the process uses an executable
stack or not. The second argument is not used by anybody, it could
be removed without replacement.
What actually does make sense is to pass an indication if the process
uses the elf interpreter or not. The glibc code will not use anything
from the vdso if the process does not use the dynamic linker, so for
statically linked binaries the architecture backend can choose not
to map the vdso.
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
And as it looks like only s390 ever made use of this optimization,
which now isn't an optimization anymore. So this can simply be
removed.
commit cf6ac72fdd2026e91c0672ccf0eefd2e58920bdc
Author: Stefan Liebler <stli@linux.ibm.com>
Date: Tue Aug 6 14:15:09 2019 +0200
s390: Fix Enable VDSO for static linking
The commit 5e855c8954014bca7b0d6f07312ec09553695ffd
"s390: Enable VDSO for static linking" removed the definition of VDSO_SETUP
which leads to not setup the vdso symbols.
Instead it jumps to false addresses.
This patch just re adds the removed VDSO_SETUP macro definition.
ChangeLog:
* sysdeps/unix/sysv/linux/s390/init-first.c (VDSO_SETUP): New define.
@@ -53,4 +53,6 @@ _libc_vdso_platform_setup (void)
VDSO_SYMBOL (getcpu) = p;
}
+#define VDSO_SETUP _libc_vdso_platform_setup
+
#include <csu/init-first.c>