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Message-ID: <20171005090633.5a6ce840@gandalf.local.home> Date: Thu, 5 Oct 2017 09:06:33 -0400 From: Steven Rostedt <rostedt@...dmis.org> To: Thomas Garnier <thgarnie@...gle.com> Cc: Herbert Xu <herbert@...dor.apana.org.au>, "David S . Miller" <davem@...emloft.net>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>, Peter Zijlstra <peterz@...radead.org>, Josh Poimboeuf <jpoimboe@...hat.com>, Arnd Bergmann <arnd@...db.de>, Kees Cook <keescook@...omium.org>, Matthias Kaehlcke <mka@...omium.org>, Tom Lendacky <thomas.lendacky@....com>, Andy Lutomirski <luto@...nel.org>, "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>, Borislav Petkov <bp@...e.de>, "Rafael J . Wysocki" <rjw@...ysocki.net>, Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>, Juergen Gross <jgross@...e.com>, Chris Wright <chrisw@...s-sol.org>, Alok Kataria <akataria@...are.com>, Rusty Russell <rusty@...tcorp.com.au>, Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>, Boris Ostrovsky <boris.ostrovsky@...cle.com>, Alexey Dobriyan <adobriyan@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, Paul Gortmaker <paul.gortmaker@...driver.com>, Chris Metcalf <cmetcalf@...lanox.com>, "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>, Nicolas Pitre <nicolas.pitre@...aro.org>, Borislav Petkov <bp@...en8.de>, "Luis R . Rodriguez" <mcgrof@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Christopher Li <sparse@...isli.org>, Jason Baron <jbaron@...mai.com>, Dou Liyang <douly.fnst@...fujitsu.com>, "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>, Mika Westerberg <mika.westerberg@...ux.intel.com>, Lukas Wunner <lukas@...ner.de>, Masahiro Yamada <yamada.masahiro@...ionext.com>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Markus Trippelsdorf <markus@...ppelsdorf.de>, Paolo Bonzini <pbonzini@...hat.com>, Radim Krčmář <rkrcmar@...hat.com>, Joerg Roedel <joro@...tes.org>, Rik van Riel <riel@...hat.com>, David Howells <dhowells@...hat.com>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, Waiman Long <longman@...hat.com>, Kyle Huey <me@...ehuey.com>, Andrey Ryabinin <aryabinin@...tuozzo.com>, Jonathan Corbet <corbet@....net>, Matthew Wilcox <mawilcox@...rosoft.com>, Michal Hocko <mhocko@...e.com>, Peter Foley <pefoley2@...oley.com>, Paul Bolle <pebolle@...cali.nl>, Jiri Kosina <jkosina@...e.cz>, Rob Landley <rob@...dley.net>, "H . J . Lu" <hjl.tools@...il.com>, Baoquan He <bhe@...hat.com>, "Jan H . Schönherr" <jschoenh@...zon.de>, Daniel Micay <danielmicay@...il.com>, x86@...nel.org, linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org, virtualization@...ts.linux-foundation.org, xen-devel@...ts.xenproject.org, linux-arch@...r.kernel.org, linux-sparse@...r.kernel.org, kvm@...r.kernel.org, linux-doc@...r.kernel.org, kernel-hardening@...ts.openwall.com Subject: Re: [RFC v3 20/27] x86/ftrace: Adapt function tracing for PIE support On Wed, 4 Oct 2017 14:19:56 -0700 Thomas Garnier <thgarnie@...gle.com> wrote: > When using -fPIE/PIC with function tracing, the compiler generates a > call through the GOT (call *__fentry__@...PCREL). This instruction > takes 6 bytes instead of 5 on the usual relative call. > > With this change, function tracing supports 6 bytes on traceable > function and can still replace relative calls on the ftrace assembly > functions. > > Position Independent Executable (PIE) support will allow to extended the > KASLR randomization range below the -2G memory limit. Question: This 6 bytes is only the initial call that gcc creates. When function tracing is enabled, the calls are back to the normal call to the ftrace trampoline? -- Steve
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