From: will.deacon@arm•com (Will Deacon)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v7 8/9] ARM: vdso initialization, mapping, and synchronization
Date: Wed, 2 Jul 2014 17:27:26 +0100 [thread overview]
Message-ID: <20140702162726.GG24879@arm.com> (raw)
In-Reply-To: <53B430F3.9070804@mentor.com>
On Wed, Jul 02, 2014 at 05:18:59PM +0100, Nathan Lynch wrote:
> On 07/02/2014 10:54 AM, Andy Lutomirski wrote:
> > Caveat 2: (major) I'm kind of surprised that this, or the current
> > code, works reliably. You're doing something that I tried briefly for
> > x86_64:
> >
> > _end = .;
> > PROVIDE(end = .);
> >
> > . = ALIGN(PAGE_SIZE);
> > PROVIDE(_vdso_data = .);
> >
> > This sounds great, except that you're assuming that vdso_end -
> > vdso_start == ALIGN(_end, PAGE_SIZE) - (vdso base address).
> >
> > If you *fully* strip the vdso (eu-strip --strip-sections), then this
> > is true: eu-strip --strip-sections outputs just the PT_LOAD piece of
> > the vdso. But any binutils-generated incompletely stripped ELF image
> > contains a section table and possible non-allocatable sections at the
> > end. If these exceed the amount of unused space in the last PT_LOAD
> > page, then they'll spill into the next page, and _vdso_data in the
> > vdso will no longer match the address at which vdso.c loads it. Boom!
> >
> > I bet you're getting away with this because the whole arm64 vdso seems
> > to be written in assembly, so it seems extremely unlikely to exceed
> > one page minus a few hundred bytes. But if you start adding
> > complexity, you might get unlucky.
>
> This is why I switched (in v5) the proposed 32-bit ARM VDSO to place the
> data page before the code -- adding -frecord-gcc-switches to the
> compiler flags was enough to break it.
>
> I meant to call Will's attention to it at the time for arm64's sake, but
> I guess it slipped my mind... sorry.
Hmm, so I could definitely look at doing the same thing, but I don't know if
we actually need to for arm64. As Andy points out, we're written entirely in
assembly and we objcopy -S to create the vdso.so. I've dumped the headers
below and everything appears to be PT_LOAD.
Will
--->8
arch/arm64/kernel/vdso/vdso.so: file format elf64-littleaarch64
arch/arm64/kernel/vdso/vdso.so
architecture: aarch64, flags 0x00000150:
HAS_SYMS, DYNAMIC, D_PAGED
start address 0x00000000000002d0
Program Header:
LOAD off 0x0000000000000000 vaddr 0x0000000000000000 paddr 0x0000000000000000 align 2**4
filesz 0x00000000000006e8 memsz 0x00000000000006e8 flags r-x
DYNAMIC off 0x00000000000005d8 vaddr 0x00000000000005d8 paddr 0x00000000000005d8 align 2**3
filesz 0x00000000000000f0 memsz 0x00000000000000f0 flags r--
NOTE off 0x00000000000002b8 vaddr 0x00000000000002b8 paddr 0x00000000000002b8 align 2**2
filesz 0x0000000000000018 memsz 0x0000000000000018 flags r--
EH_FRAME off 0x00000000000004f0 vaddr 0x00000000000004f0 paddr 0x00000000000004f0 align 2**2
filesz 0x0000000000000034 memsz 0x0000000000000034 flags r--
Dynamic Section:
SONAME linux-vdso.so.1
HASH 0x0000000000000120
STRTAB 0x00000000000001f8
SYMTAB 0x0000000000000150
STRSZ 0x0000000000000077
SYMENT 0x0000000000000018
VERDEF 0x0000000000000280
VERDEFNUM 0x0000000000000002
VERSYM 0x0000000000000270
Version definitions:
1 0x01 0x0deebfa1 linux-vdso.so.1
2 0x00 0x075fcb89 LINUX_2.6.39
private flags = 0:
Sections:
Idx Name Size VMA LMA File off Algn
0 .hash 00000030 0000000000000120 0000000000000120 00000120 2**3
CONTENTS, ALLOC, LOAD, READONLY, DATA
1 .dynsym 000000a8 0000000000000150 0000000000000150 00000150 2**3
CONTENTS, ALLOC, LOAD, READONLY, DATA
2 .dynstr 00000077 00000000000001f8 00000000000001f8 000001f8 2**0
CONTENTS, ALLOC, LOAD, READONLY, DATA
3 .gnu.version 0000000e 0000000000000270 0000000000000270 00000270 2**1
CONTENTS, ALLOC, LOAD, READONLY, DATA
4 .gnu.version_d 00000038 0000000000000280 0000000000000280 00000280 2**3
CONTENTS, ALLOC, LOAD, READONLY, DATA
5 .note 00000018 00000000000002b8 00000000000002b8 000002b8 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA, LINK_ONCE_SAME_CONTENTS
6 .text 00000220 00000000000002d0 00000000000002d0 000002d0 2**4
CONTENTS, ALLOC, LOAD, READONLY, CODE
7 .eh_frame_hdr 00000034 00000000000004f0 00000000000004f0 000004f0 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
8 .eh_frame 000000b0 0000000000000528 0000000000000528 00000528 2**3
CONTENTS, ALLOC, LOAD, READONLY, DATA
9 .dynamic 000000f0 00000000000005d8 00000000000005d8 000005d8 2**3
CONTENTS, ALLOC, LOAD, DATA
10 .got 00000008 00000000000006c8 00000000000006c8 000006c8 2**3
CONTENTS, ALLOC, LOAD, DATA
11 .got.plt 00000018 00000000000006d0 00000000000006d0 000006d0 2**3
CONTENTS, ALLOC, LOAD, DATA
SYMBOL TABLE:
no symbols
next prev parent reply other threads:[~2014-07-02 16:27 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-23 3:11 [PATCH v7 0/9] ARM: VDSO Nathan Lynch
2014-06-23 3:11 ` [PATCH v7 1/9] clocksource: arm_arch_timer: change clocksource name if CP15 unavailable Nathan Lynch
2014-06-23 3:11 ` [PATCH v7 2/9] clocksource: arm_arch_timer: enable counter access for 32-bit ARM Nathan Lynch
2014-06-23 3:11 ` [PATCH v7 3/9] ARM: arch_timer: remove unused functions Nathan Lynch
2014-06-23 3:11 ` [PATCH v7 4/9] arm64: " Nathan Lynch
2014-06-23 3:11 ` [PATCH v7 5/9] ARM: place sigpage at a random offset above stack Nathan Lynch
2014-06-23 3:11 ` [PATCH v7 6/9] ARM: miscellaneous vdso infrastructure, preparation Nathan Lynch
2014-06-30 10:11 ` Arnd Bergmann
2014-06-30 12:27 ` Nathan Lynch
2014-06-30 13:06 ` Arnd Bergmann
2014-06-23 3:11 ` [PATCH v7 7/9] ARM: add vdso user-space code Nathan Lynch
2014-06-28 9:53 ` Russell King - ARM Linux
2014-06-28 10:03 ` Russell King - ARM Linux
2014-06-30 15:56 ` Andy Lutomirski
2014-06-28 15:19 ` Nathan Lynch
2014-06-28 15:26 ` Russell King - ARM Linux
2014-06-28 16:13 ` Nathan Lynch
2014-06-28 18:12 ` Russell King - ARM Linux
2014-06-28 19:45 ` Nathan Lynch
2014-06-28 20:11 ` Russell King - ARM Linux
2014-06-28 21:35 ` Nathan Lynch
2014-06-29 8:34 ` Russell King - ARM Linux
2014-06-29 15:48 ` Nathan Lynch
2014-06-29 16:07 ` Russell King - ARM Linux
2014-06-29 23:04 ` Nathan Lynch
2014-06-30 21:33 ` Andy Lutomirski
2014-06-30 15:59 ` Andy Lutomirski
2014-06-30 16:50 ` Nathan Lynch
2014-06-30 21:29 ` Andy Lutomirski
2014-07-01 9:00 ` Will Deacon
2014-07-01 13:34 ` Nathan Lynch
2014-07-01 14:11 ` Andy Lutomirski
2014-07-01 13:28 ` Nathan Lynch
2014-07-01 14:56 ` Andy Lutomirski
2014-06-23 3:11 ` [PATCH v7 8/9] ARM: vdso initialization, mapping, and synchronization Nathan Lynch
2014-06-30 21:37 ` Andy Lutomirski
2014-07-01 9:03 ` Will Deacon
2014-07-01 14:11 ` Nathan Lynch
2014-07-01 14:15 ` Will Deacon
2014-07-01 14:17 ` Andy Lutomirski
2014-07-01 17:27 ` Christopher Covington
2014-07-02 14:40 ` Will Deacon
2014-07-02 15:54 ` Andy Lutomirski
2014-07-02 16:18 ` Nathan Lynch
2014-07-02 16:27 ` Will Deacon [this message]
2014-07-02 16:47 ` Andy Lutomirski
2014-07-02 17:24 ` Will Deacon
2014-07-02 18:34 ` Andy Lutomirski
2014-07-02 18:54 ` Will Deacon
2014-07-22 0:14 ` Andy Lutomirski
2014-07-22 8:13 ` Will Deacon
2014-07-01 14:01 ` Nathan Lynch
2014-07-01 14:09 ` Andy Lutomirski
2014-07-01 14:14 ` Russell King - ARM Linux
2014-06-23 3:11 ` [PATCH v7 9/9] ARM: add CONFIG_VDSO Kconfig and Makefile bits Nathan Lynch
2014-06-27 8:51 ` [PATCH v7 0/9] ARM: VDSO Jan Glauber
2014-06-27 8:57 ` Russell King - ARM Linux
2014-06-27 9:41 ` Ard Biesheuvel
2014-06-27 9:46 ` Russell King - ARM Linux
2014-06-27 17:01 ` Nathan Lynch
2014-06-28 9:42 ` Russell King - ARM Linux
2014-06-28 9:55 ` Russell King - ARM Linux
2014-06-28 14:49 ` Russell King - ARM Linux
2014-06-30 7:27 ` Arnd Bergmann
2014-06-30 7:43 ` Arnd Bergmann
2014-06-30 18:27 ` Nathan Lynch
2014-06-27 16:00 ` Nathan Lynch
2014-06-30 16:03 ` Andy Lutomirski
2014-06-30 8:12 ` Ard Biesheuvel
2014-07-01 16:34 ` Nathan Lynch
2014-07-01 20:08 ` Ard Biesheuvel
2014-07-01 22:44 ` Russell King - ARM Linux
2014-06-30 14:40 ` Will Deacon
2014-06-30 15:42 ` Nathan Lynch
2014-06-30 21:56 ` Andy Lutomirski
2014-07-01 9:04 ` Will Deacon
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