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Message-ID: <20160308142134.GB16832@treble.hsd1.ky.comcast.net> Date: Tue, 8 Mar 2016 08:21:34 -0600 From: Josh Poimboeuf <jpoimboe@...hat.com> To: Ingo Molnar <mingo@...nel.org> Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org, linux-kernel@...r.kernel.org, live-patching@...r.kernel.org, Michal Marek <mmarek@...e.cz>, Peter Zijlstra <peterz@...radead.org>, Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...en8.de>, Linus Torvalds <torvalds@...ux-foundation.org>, Andi Kleen <andi@...stfloor.org>, Pedro Alves <palves@...hat.com>, Namhyung Kim <namhyung@...il.com>, Bernd Petrovitsch <bernd@...rovitsch.priv.at>, Chris J Arges <chris.j.arges@...onical.com>, Andrew Morton <akpm@...ux-foundation.org>, Jiri Slaby <jslaby@...e.cz>, Arnaldo Carvalho de Melo <acme@...nel.org> Subject: Re: [PATCH v19 00/10] Compile-time stack metadata validation On Tue, Mar 08, 2016 at 02:44:57PM +0100, Ingo Molnar wrote: > > * Josh Poimboeuf <jpoimboe@...hat.com> wrote: > > > On Tue, Mar 08, 2016 at 11:37:16AM +0100, Ingo Molnar wrote: > > > > > > * Josh Poimboeuf <jpoimboe@...hat.com> wrote: > > > > > > > This is v19 of the compile-time stack metadata validation patch set. > > > > > > > > It's based on tip:core/objtool. > > > > > > So I've upgraded my main build box to Fedora 23, to: > > > > > > gcc version 5.3.1 20151207 (Red Hat 5.3.1-2) (GCC) > > > GNU assembler version 2.25 (x86_64-redhat-linux) using BFD version version 2.25-15.fc23 > > > GNU ld version 2.25-15.fc23 > > > > > > and I'm now getting a bunch of these warnings: > > > > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x2e7: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x2f3: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x2ff: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x30b: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x317: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x323: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x32f: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x33b: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x348: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x355: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x362: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x36f: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x37c: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x389: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x396: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x2e7: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x2f3: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x2ff: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x30b: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x317: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x323: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x32f: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x33b: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x348: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x355: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x362: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x36f: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x37c: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x389: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x396: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x19a: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x1a6: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x1b2: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x1be: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x1ca: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x1d6: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x1e2: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x1ee: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x1ff: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x210: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x221: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x251: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x262: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x273: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x284: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x295: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x2a6: frame pointer state mismatch > > > drivers/net/wireless/realtek/rtlwifi/base.o: warning: objtool: rtlwifi_rate_mapping()+0x2b7: frame pointer state mismatch > > > > > > I see nothing particularly weird about rtlwifi_rate_mapping(), except the tons of > > > switch statements - maybe GCC does something really clever here? > > > > > > In any case this needs to be addressed before the merge window. Also, I think we > > > should limit the number of objtool warnings to one per function? > > > > This is a bug in objtool's handling of switch statement jump tables. In > > fact, the 0-day bot warned me about this bug yesterday, but I > > misinterpreted it: > > > > https://lkml.kernel.org/r/201603060006.yNZ9xTcs%fengguang.wu@intel.com > > > > I'll fix it up today. I'll also limit the warnings to one per function. > > > > BTW, I was only able to recreate this particular issue after updating to > > today's tip/master. It was triggered by a new config option: > > CONFIG_UBSAN_SANITIZE_ALL. > > ah, makes sense! I also upgraded to the latestest Fedora and misinterpreted the > warning. > > Btw., I like it how in other cases you didn't try to work the warning around in > objtool, but improved the C code itself. We can consider this warning as a > 'unnecessarily complex switch statement' warning. So the bug is that when there's more than one switch statement in a function, objtool interprets all the switch jump tables as a single table. If the targets of one jump table assume a stack frame and the targets of another one don't, you'll see frame pointer warnings like those above. It *is* interesting that both functions which triggered this bug -- rtlwifi_rate_mapping() and cik_tiling_mode_table_init() -- are cases where the code is way too complex and can be simplified. But, unless we want to institute an "only one switch statement allowed per function" policy, I think I should still fix the bug. Because I don't really have the clout to tell people "you need to clean up your code because my tool is buggy." :-) -- Josh
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