Bug 959013

Summary:	x86_64 vDSO has grown 4KB -> 8KB
Product:	[Fedora] Fedora	Reporter:	Jan Kratochvil <jan.kratochvil>
Component:	kernel	Assignee:	Kernel Maintainer List <kernel-maint>
Status:	CLOSED NOTABUG	QA Contact:	Fedora Extras Quality Assurance <extras-qa>
Severity:	low	Docs Contact:
Priority:	low
Version:	18	CC:	gansalmon, itamar, jan.kratochvil, jonathan, kernel-maint, madhu.chinakonda, roland
Target Milestone:	---
Target Release:	---
Hardware:	x86_64
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:	312011	Environment:
Last Closed:	2013-07-24 20:22:27 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	312011
Bug Blocks:

Description Jan Kratochvil 2013-05-03 01:30:08 UTC

+++ This bug was initially created as a clone of Bug #312011 +++

Description of problem:
on recent x86_64 kernels the kernel VDSO has grown from 4KB to 8KB.
This affects reading debug info of vDSO in various GDB variants.

Version-Release number of selected component (if applicable):
kernel-3.8.8-202.fc18.x86_64

How reproducible:
Always.

Steps to Reproduce:
cat /proc/self/maps | grep vdso

Actual results:
7fff9db67000-7fff9db69000 r-xp 00000000 00:00 0 [vdso]

Expected results:
7fff9db67000-7fff9db68000 r-xp 00000000 00:00 0 [vdso]

Comment 2 Josh Boyer 2013-07-02 16:23:59 UTC

As far as I can tell, the text section itself of vdso.so is almost 4K.  When combined with the rest of the sections, the overall size of the vdso is 5560 bytes (on a 3.9.6-301 f19 kernel).  That is then page aligned, so we get 8K total.

I might be missing something, but unlike the original bug I don't see the vDSO being fully contained within a single page?  So it seems comment #3 from that bug might still be applicable.

If I've missed something, please let me know.

Comment 3 Jan Kratochvil 2013-07-24 20:22:27 UTC

At least kernel-3.10.0-2.el7.x86_64 has:

Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  LOAD           0x0000000000000000 0xffffffffff700000 0xffffffffff700000
                 0x000000000000102d 0x000000000000102d  R E    1000

so it should not be a problem.

It was not a case for kernel-3.9.9-201.fc18.x86_64 but let's forget about F-18.

Problem was when the runtime (segment) informatio was 4KB but some sections (debug) information were 8KB, they were cut then.

Confirming that it seems vDSO really contains so much code nowadays.