From: "H. Peter Anvin" <hpa@zytor.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: nicolas.pitre@linaro.org, linux-mips@linux-mips.org,
linux-sh@vger.kernel.org, benh@kernel.crashing.org,
Will Deacon <will.deacon@arm.com>,
paulus@samba.org, mpe@ellerman.id.au, jejb@parisc-linux.org,
Geert Uytterhoeven <geert@linux-m68k.org>,
Catalin Marinas <catalin.marinas@arm.com>,
gor@linux.vnet.ibm.com, mattst88@gmail.com,
uclinux-h8-devel@lists.sourceforge.jp,
Marc Zyngier <marc.zyngier@arm.com>,
linuxram@us.ibm.com, linux-um@lists.infradead.org,
Nicholas Piggin <npiggin@gmail.com>,
luto@kernel.org, shannon.nelson@oracle.com,
Thomas Gleixner <tglx@linutronix.de>,
alex.bennee@linaro.org, rth@twiddle.net, jkosina@suse.cz,
Nick Desaulniers <ndesaulniers@google.com>,
LKML <linux-kernel@vger.kernel.org>,
ralf@linux-mips.org, rkuo@codeaurora.org, paul.burton@mips.com,
aneesh.kumar@linux.vnet.ibm.com,
Greg KH <gregkh@linuxfoundation.org>,
Andrew Morton <akpm@linux-found>
Subject: Re: [PATCH] treewide: remove current_text_addr
Date: Mon, 27 Aug 2018 06:33:27 -0700 [thread overview]
Message-ID: <4d1a8f35-e2fc-70d2-ca0e-44b8574c86f1@zytor.com> (raw)
In-Reply-To: <20180827131103.GD24124@hirez.programming.kicks-ass.net>
On 08/27/18 06:11, Peter Zijlstra wrote:
> On Mon, Aug 27, 2018 at 05:26:53AM -0700, H. Peter Anvin wrote:
>
>> _THIS_IP_, however, is completely ill-defined, other than being an
>> address *somewhere* in the same global function (not even necessarily
>> the same function if the function is static!) As my experiment show, in
>> many (nearly) cases gcc will hoist the address all the way to the top of
>> the function, at least for the current generic implementation.
>
> It seems to have mostly worked so far... did anything change?
>
Most likely because the major architectures contain a arch-specific
assembly implementation. The generic implementation used in some places
is completely broken, as my experiments show.
>> For the case where _THIS_IP_ is passed to an out-of-line function in all
>> cases, it is extra pointless because all it does is increase the
>> footprint of every caller: _RET_IP_ is inherently passed to the function
>> anyway, and with tailcall protection it will uniquely identify a callsite.
>
> So I think we can convert many of the lockdep _THIS_IP_ calls to
> _RET_IP_ on the other side, with a wee bit of care.
>
> A little something like so perhaps...
I don't have time to look at this right now (I'm on sabbatical, and I'm
dealing with personal legal stuff right at the moment), but I think it
is the right direction.
-hpa
next prev parent reply other threads:[~2018-08-27 13:33 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAKwvOdkWL_2yTnJqM6n6R9UCPwY4iz-9BQYGN2MDAk9EzumUvA@mail.gmail.com>
[not found] ` <20180821202900.208417-1-ndesaulniers@google.com>
[not found] ` <207784db-4fcc-85e7-a0b2-fec26b7dab81@gmx.de>
2018-08-26 2:38 ` [PATCH] treewide: remove current_text_addr H. Peter Anvin
2018-08-26 3:16 ` H. Peter Anvin
2018-08-26 4:56 ` H. Peter Anvin
2018-08-26 19:30 ` H. Peter Anvin
2018-08-26 20:25 ` Linus Torvalds
2018-08-27 2:52 ` Nick Desaulniers
2018-08-27 7:33 ` Peter Zijlstra
2018-08-27 12:26 ` H. Peter Anvin
2018-08-27 13:11 ` Peter Zijlstra
2018-08-27 13:33 ` H. Peter Anvin [this message]
2018-08-31 16:48 ` Nick Desaulniers
2018-08-27 7:43 ` Nicholas Piggin
2018-08-26 23:20 ` H. Peter Anvin
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