From: luto@amacapital•net (Andy Lutomirski)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v7 7/9] ARM: add vdso user-space code
Date: Mon, 30 Jun 2014 08:56:03 -0700 [thread overview]
Message-ID: <53B18893.6040701@amacapital.net> (raw)
In-Reply-To: <20140628100347.GE32514@n2100.arm.linux.org.uk>
On 06/28/2014 03:03 AM, Russell King - ARM Linux wrote:
> On Sat, Jun 28, 2014 at 10:53:14AM +0100, Russell King - ARM Linux wrote:
>> On Sun, Jun 22, 2014 at 10:11:56PM -0500, Nathan Lynch wrote:
>>> Place vdso-related user-space code in arch/arm/kernel/vdso/.
>>>
>>> It is almost completely written in C with some assembly helpers to
>>> load the data page address, sample the counter, and fall back to
>>> system calls when necessary.
>>>
>>> If CONFIG_ARM_ARCH_TIMER is not enabled, the vdso cannot service
>>> high-resolution clocks and falls back to syscalls. Low-resolution
>>> clocks e.g. CLOCK_REALTIME_COARSE can be serviced regardless.
>>>
>>> Of particular note is that a post-processing step ("vdsomunge") is
>>> necessary to produce a shared object which is architecturally allowed
>>> to be used by both soft- and hard-float EABI programs.
>>>
>>> The 2012 edition of the ARM ABI defines Tag_ABI_VFP_args = 3 "Code is
>>> compatible with both the base and VFP variants; the user did not
>>> permit non-variadic functions to pass FP parameters/results."
>>> Unfortunately current toolchains do not support this tag, which is
>>> ideally what we would use.
>>>
>>> The best available option is to ensure that both EF_ARM_ABI_FLOAT_SOFT
>>> and EF_ARM_ABI_FLOAT_HARD are unset in the ELF header's e_flags,
>>> indicating that the shared object is "old" and should be accepted for
>>> backward compatibility's sake. While binutils < 2.24 appear to
>>> produce a vdso.so with both flags clear, 2.24 always sets
>>> EF_ARM_ABI_FLOAT_SOFT, with no way to inhibit this behavior. So we
>>> have to fix things up with a custom post-processing step.
>>>
>>> In fact, the VDSO code in glibc does much less validation (including
>>> checking these flags) than the code for handling conventional
>>> file-backed shared libraries, so this is a bit moot unless glibc's
>>> VDSO code becomes more strict.
>>>
>>> Signed-off-by: Nathan Lynch <nathan_lynch@mentor•com>
>>> ---
>>> arch/arm/kernel/asm-offsets.c | 5 +
>>> arch/arm/kernel/vdso/.gitignore | 1 +
>>> arch/arm/kernel/vdso/Makefile | 59 +++++++
>>> arch/arm/kernel/vdso/checkundef.sh | 9 +
>>> arch/arm/kernel/vdso/datapage.S | 15 ++
>>> arch/arm/kernel/vdso/vdso.S | 35 ++++
>>> arch/arm/kernel/vdso/vdso.lds.S | 88 ++++++++++
>>> arch/arm/kernel/vdso/vdsomunge.c | 193 +++++++++++++++++++++
>>> arch/arm/kernel/vdso/vgettimeofday.c | 320 +++++++++++++++++++++++++++++++++++
>>> 9 files changed, 725 insertions(+)
>>> create mode 100644 arch/arm/kernel/vdso/.gitignore
>>> create mode 100644 arch/arm/kernel/vdso/Makefile
>>> create mode 100755 arch/arm/kernel/vdso/checkundef.sh
>>> create mode 100644 arch/arm/kernel/vdso/datapage.S
>>> create mode 100644 arch/arm/kernel/vdso/vdso.S
>>> create mode 100644 arch/arm/kernel/vdso/vdso.lds.S
>>> create mode 100644 arch/arm/kernel/vdso/vdsomunge.c
>>> create mode 100644 arch/arm/kernel/vdso/vgettimeofday.c
>>
>> One change I would like to see (to stop the directory tree getting soo
>> deep) is to move this to arch/arm/vdso - just like x86 is arch/x86/vdso.
>> Was there a pressing reason to have it in arch/arm/kernel ?
>
> It also looks like there's something missing for vdso_install to work.
> arch/x86 has this:
>
> PHONY += vdso_install
> vdso_install:
> $(Q)$(MAKE) $(build)=arch/x86/vdso $@
>
> but doesn't list it in the arch help. I'm sure we can do better on ARM. :)
In 3.16-rc3 this is rather improved, albeit still undocumented. It's
probably worth matching x86's behavior for gdb's benefit.
--Andy
next prev parent reply other threads:[~2014-06-30 15:56 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 [this message]
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
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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