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Fri, 01 Dec 2023 14:59:47 -0800 (PST) Message-ID: <4597db06-dabc-4bb2-9f24-bd30e07ff86d@broadcom.com> Date: Fri, 1 Dec 2023 14:59:45 -0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: ARM Ftrace Function Graph Fails With UNWINDER_FRAME_POINTER To: Steven Rostedt Cc: Ard Biesheuvel , mhiramat@kernel.org, mark.rutland@arm.com, linux@armlinux.org.uk, linux-trace-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Florian Fainelli , Doug Berger References: <81af85b4-5274-4362-9413-890425c60524@broadcom.com> <20231201130702.2824115c@gandalf.local.home> From: Justin Chen In-Reply-To: <20231201130702.2824115c@gandalf.local.home> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20231201_145951_472082_76060CBD X-CRM114-Status: GOOD ( 23.33 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: multipart/mixed; boundary="===============6348939340585415049==" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org --===============6348939340585415049== Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-256; boundary="000000000000a716f3060b7ab975" --000000000000a716f3060b7ab975 Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 12/1/23 10:07 AM, Steven Rostedt wrote: > On Fri, 1 Dec 2023 09:25:59 -0800 > Justin Chen wrote: > >>> It appears the sub instruction at 0x6dd0 correctly accounts for the >>> extra 8 bytes, so the frame pointer is valid. So it is our assumption >>> that there are no gaps between the stack frames is invalid. >> >> Thanks for the assistance. The gap between the stack frame depends on >> the function. Most do not have a gap. Some have 8 (as shown above), some >> have 12. A single assumption here is not going to work. I'm having a >> hard time finding out the reasoning for this gap. I tried disabling a >> bunch of gcc flags as well as -O2 and the gap still exists. > > That code was originally added because of some strange things that gcc did > with mcount (for example, it made a copy of the stack frame that it passed > to mcount, where the function graph tracer replaced the copy of the return > stack making the shadow stack go out of sync and crash). This was very hard > to debug and I added this code to detect it if it happened again. > > Well it's been over a decade since that happened (2009). > > 71e308a239c09 ("function-graph: add stack frame test") > > I'm happy assuming that the compiler folks are aware of our tricks with > hijacking return calls and I don't expect it to happen again. We can just > rip out those checks. That is, if it's only causing false positives, I > don't think it's worth keeping around. > > Has it detected any real issues on the Arm platforms? > > -- Steve I am not familiar enough to make a call. But from my limited testing with ARM, I didn't see any issues. If you would like me to, I can submit a patch to remove the check entirely. Or maybe only disable it for ARM? Thanks, Justin --000000000000a716f3060b7ab975 Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIIQagYJKoZIhvcNAQcCoIIQWzCCEFcCAQExDzANBglghkgBZQMEAgEFADALBgkqhkiG9w0BBwGg gg3BMIIFDTCCA/WgAwIBAgIQeEqpED+lv77edQixNJMdADANBgkqhkiG9w0BAQsFADBMMSAwHgYD VQQLExdHbG9iYWxTaWduIFJvb3QgQ0EgLSBSMzETMBEGA1UEChMKR2xvYmFsU2lnbjETMBEGA1UE AxMKR2xvYmFsU2lnbjAeFw0yMDA5MTYwMDAwMDBaFw0yODA5MTYwMDAwMDBaMFsxCzAJBgNVBAYT AkJFMRkwFwYDVQQKExBHbG9iYWxTaWduIG52LXNhMTEwLwYDVQQDEyhHbG9iYWxTaWduIEdDQyBS MyBQZXJzb25hbFNpZ24gMiBDQSAyMDIwMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA vbCmXCcsbZ/a0fRIQMBxp4gJnnyeneFYpEtNydrZZ+GeKSMdHiDgXD1UnRSIudKo+moQ6YlCOu4t rVWO/EiXfYnK7zeop26ry1RpKtogB7/O115zultAz64ydQYLe+a1e/czkALg3sgTcOOcFZTXk38e aqsXsipoX1vsNurqPtnC27TWsA7pk4uKXscFjkeUE8JZu9BDKaswZygxBOPBQBwrA5+20Wxlk6k1 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--000000000000a716f3060b7ab975-- --===============6348939340585415049== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel --===============6348939340585415049==--