Whoops wrong compiler. Here is an update. I added the flags so this one reproduces the issue.
https://godbolt.org/#z:OYLghAFBqd5QCxAYwPYBMCmBRdBLAF1QCcAaPECAMzwBtMA7AQwFtMQByARg9KtQYEAysib0QXACx8BBAKoBnTAAUAHpwAMvAFYTStJg1DIApACYAQuYukl9ZATwDKjdAGFUtAK4sGIM6SuADJ4DJgAcj4ARpjEINIADqgKhE4MHt6%2B/qRJKY4CIWGRLDFx0naYDmlCBEzEBBk%2BfgEVVQI1dQSFEdGx8ba19Y1ZLYNdoT0lfZIAlLaoXsTI7BwA9KsA1AAqAJ4JmBs7C8QbaFgbCLGYpBskG7SoTOgbhhuYqqwJ9AB0JhoAgqECBsFABHLx1TAQIEbBg%2BGYbEwAdisAI26I2xEwBEWDFhPg2ACp8SwTABmVH/ZEAEQ4c1onAArLw/BwtKRUJw3NZrCDjstEWYyTxSARNHS5gBrECMjT6TiSFnijmcXgKEBysVsumkOCwJBoFgJOixciUQ3G%2BhxYBcMxcPh0AixdUQKLKqKhOo7Tgiw1sQQAeQYtG92tIWBYhmA4jD%2BCxVQAbph1WH3pUvE6fbwgZgGWHaHgosQvR4sMqCMQ8Cws3MqAZgAoAGp4TAAdwD%2B1ZIv4ghEYnYUhkgkUKnUYd09oMRhQPMs%2BkL6sgc1QCXyDBTAFoA2SNhvI0sEOTqQpJTsDJLMGrc5U1y4GO5PE09MEJsVSnpcqkBMM/PbP2vujfPp7VaNcOiGR8shA682gYcDxiKXo4hAsYfz0BQxkApCJDmBR%2BQHUUsRWHh6SZJUw05DhVAADgANg3WjJA2YBkGQDZbW%2BLgNggblLGsG5cEIO5zGFG4PCNE0ThErgZl4LUtDmCADVQCSrTNCALUklApxtSQNDlGhaCdYgXTdMMPWYYhQ19FT/QIIMQ2VCMoxjdk4xvPAkxTdk02QDNiOzQRc2VAsixLDAVnZCsqxrPh6ybFt207LMh2EURxEHHt5CUNRlV0AIdJnPi51CxcIGXVc0k3bdd33ZBDzJY9T3PS9bBg28IFcND7RfRCpmQnJki/dJIN/Qa8jSLD%2BvQ9rqlQ0aZvsMDMNfbCUM6bqBk6Kb3xk%2BZFmWPQK0wALSI4ZlSFZdlKJo%2BjGNOHT2Mkb4NBe7jeKsOcNkEogpKFe0NnEy1YkFMkzFk0VxUUpB8CoKh1KyvsMukLKR1y/MEHVSdMdhqgCD2dg5WITHsmJhRcfx/YNTOi6rt4SjqTwOGNmbNsQduhimJYtiOK4hMFA2Dn7uQR6pBel65KhqUZTlPNFUu5VKLVbJ5IleUODMcjrtVSHtRmOYkxMtJ4iAA Thanks, Andrew Fish > On May 18, 2023, at 11:45 AM, Andrew Fish via groups.io > <afish=apple....@groups.io> wrote: > > Mike, > > This is a good way to play around with fixes, and to report bugs. You can see > the assembler for different compilers with different flag. > > https://godbolt.org/#z:OYLghAFBqd5QCxAYwPYBMCmBRdBLAF1QCcAaPECAMzwBtMA7AQwFtMQByARg9KtQYEAysib0QXACx8BBAKoBnTAAUAHpwAMvAFYTStJg1DIApACYAQuYukl9ZATwDKjdAGFUtAK4sGIM6SuADJ4DJgAcj4ARpjEINIADqgKhE4MHt6%2B/qRJKY4CIWGRLDFx0naYDmlCBEzEBBk%2BfgEVVQI1dQSFEdGx8ba19Y1ZLYNdoT0lfZIAlLaoXsTI7BwA9KsA1AAqAJ4JmBs7C8QbaFgbCLGYpBskG7SoTOgbhhuYqqwJ9AB0JhoAgqECBsFABHLx1TAQIEbBg%2BGYbEwAdisAI26I2xEwBEWDFhPg2ACp8SwTABmVH/ZEAEQ4c1onAArLw/BwtKRUJw3NZrCDjstEWYyTxSARNHS5gBrECMjT6TiSFnijmcXgKEBysVsumkOCwJBoFgJOixciUQ3G%2BhxYBcMxcPh0AixdUQKLKqKhOo7Tgiw1sQQAeQYtG92tIWBYhmA4jD%2BCxVQAbph1WH3pUvE6fbwgZgGWHaHgosQvR4sMqCMQ8Cws3MqAZgAoAGp4TAAdwD%2B1ZIv4ghEYnYUhkgkUKnUYd09oMRhQPMs%2BkL6sgc1QCXyDBTAFoA2SNhvI0sEOTqQpJTsDJLMGrc5U1y4GO5PE09MEJsVSnpcqkBMM/PbP2vujfPp7VaNcOiGR8shA682gYcDxiKXo4hAsYfz0BQxkApCJDmBR%2BQHUUsRWHh6SZJUw05DhVAADgANg3WjJA2YBkGQDZbW%2BLgNggblLGsG5cEIO5zGFG4PCNE0ThErgZl4LUtDmCADVQCSrTNCALUklApxtSQNDlGhaCdYgXTdMMPWYYhQ19FT/QIIMQ2VCMoxjdk4xvPAkxTdk02QDNiOzQRc2VAsixLDAVnZCsqxrPh6ybFt207LMh2EURxEHHt5CUNRlV0AIdJnPi51CxcIGXVc0k3bdd33ZBDzJY9T3PS9bBg28IFcND7RfRCpmQnJki/dJIN/Qa8jSLD%2BvQ9rqlQ0aZvsMDMNfbCUM6bqBk6Kb3xk%2BZFmWPQK0wALSI4ZlSFZdlKJo%2BjGNOHT2Mkb4NBe7jeKsOcNkEogpKFe0NnEy1YkFMkzFk0VxUUpB8CoKh1KyvsMukLKR1y/MEHVSdMdhqgCD2dg5WITHsmJhRcfx/YNTOi6rt4SjqTwOGNmbNsQduhimJYtiOK4hMFA2Dn7uQR6pBel65KhqUZTlPNFUu5VKLVbJ5IleUODMcjrtVSHtRmOYkxMtJ4iAA > > Sorry I’m traveling and in Cupertino with lots of meetings so I did not have > time to adjust the compiler flags…. > > Thanks, > > Andrew Fish > >> On May 18, 2023, at 10:24 AM, Andrew (EFI) Fish <af...@apple.com> wrote: >> >> Mike, >> >> I guess my other question… If this turns out to be a compiler bug should we >> scope the change to the broken toolchain. I’m not sure what the right answer >> is for that, but I want to ask the question? >> >> Thanks, >> >> Andrew Fish >> >>> On May 18, 2023, at 10:19 AM, Michael D Kinney <michael.d.kin...@intel.com> >>> wrote: >>> >>> Andrew, >>> >>> This might work for XIP. Set non const global to initial value that is >>> expected value to stay in dead loop. >>> >>> UINTN mDeadLoopCount = 0; >>> >>> VOID >>> CpuDeadLoop( >>> VOID >>> ) >>> { >>> while (mDeadLoopCount == 0) { >>> CpuPause(); >>> } >>> } >>> >>> When deadloop is entered, developer can not change value of mDeadLoopCount, >>> but they can use debugger to force exit loop and return from function. >>> >>> Mike >>> >>> >>> From: Andrew (EFI) Fish <af...@apple.com <mailto:af...@apple.com>> >>> Sent: Thursday, May 18, 2023 10:09 AM >>> To: Kinney, Michael D <michael.d.kin...@intel.com >>> <mailto:michael.d.kin...@intel.com>> >>> Cc: edk2-devel-groups-io <devel@edk2.groups.io >>> <mailto:devel@edk2.groups.io>>; Ni, Ray <ray...@intel.com >>> <mailto:ray...@intel.com>>; Rebecca Cran <rebe...@bsdio.com >>> <mailto:rebe...@bsdio.com>> >>> Subject: Re: [edk2-devel] CpuDeadLoop() is optimized by compiler >>> >>> Mike, >>> >>> Good point, that is why we are using the stack …. >>> >>> The only other thing I can think of is to pass the address of Index to some >>> inline assembler, or an asm no op function, to give it a side effect the >>> compiler can’t resolve. >>> >>> Thanks, >>> >>> Andrew Fish >>> >>> >>> On May 18, 2023, at 10:05 AM, Kinney, Michael D <michael.d.kin...@intel.com >>> <mailto:michael.d.kin...@intel.com>> wrote: >>> >>> Static global will not work for XIP >>> >>> Mike >>> >>> From: Andrew (EFI) Fish <af...@apple.com <mailto:af...@apple.com>> >>> Sent: Thursday, May 18, 2023 9:49 AM >>> To: edk2-devel-groups-io <devel@edk2.groups.io >>> <mailto:devel@edk2.groups.io>>; Kinney, Michael D >>> <michael.d.kin...@intel.com <mailto:michael.d.kin...@intel.com>> >>> Cc: Ni, Ray <ray...@intel.com <mailto:ray...@intel.com>>; Rebecca Cran >>> <rebe...@bsdio.com <mailto:rebe...@bsdio.com>> >>> Subject: Re: [edk2-devel] CpuDeadLoop() is optimized by compiler >>> >>> Mike, >>> >>> I pinged some compiler experts to see if our code is correct, or if the >>> compiler has an issue. Seems to be trending compiler issue right now, but >>> I’ve NOT gotten feedback from anyone on the spec committee yet. >>> >>> If we move Index to a static global that would likely work around the >>> compiler issue. >>> >>> Thanks, >>> >>> Andrew Fish >>> >>> >>> >>> On May 18, 2023, at 8:36 AM, Michael D Kinney <michael.d.kin...@intel.com >>> <mailto:michael.d.kin...@intel.com>> wrote: >>> >>> Hi Ray, >>> >>> So the code generated does deadloop, but is just not easy to resume from as >>> we have been able to do in the past. >>> >>> We use CpuDeadloop() for 2 purposes. One is a terminal condition with no >>> reason to ever continue. >>> >>> The 2nd is a debug aide for developers to halt the system at a specific >>> location and then continue from that point, usually with a debugger, to >>> step through code to an area to evaluate unexpected behavior. >>> >>> We may have to do a NASM implementation of CpuDeadloop() to make sure it >>> meets both use cases. >>> >>> Mike >>> >>> From: Ni, Ray <ray...@intel.com <mailto:ray...@intel.com>> >>> Sent: Thursday, May 18, 2023 3:00 AM >>> To: devel@edk2.groups.io <mailto:devel@edk2.groups.io> >>> Cc: Kinney, Michael D <michael.d.kin...@intel.com >>> <mailto:michael.d.kin...@intel.com>>; Rebecca Cran <rebe...@bsdio.com >>> <mailto:rebe...@bsdio.com>>; Ni, Ray <ray...@intel.com >>> <mailto:ray...@intel.com>> >>> Subject: CpuDeadLoop() is optimized by compiler >>> >>> Hi, >>> Starting from certain version of Visual Studio C compiler (I don’t have the >>> exact version. I am using VS2019), CpuDeadLoop is now optimized quite well >>> by compiler. >>> >>> The optimization is so “good” that it becomes harder for developers to >>> break out of the deadloop. >>> >>> I copied the assembly instructions as below for your reference. >>> The compiler does not generate instructions that jump out of the loop when >>> the Index is not zero. >>> So in order to break out of the loop, developers need to: >>> Manually adjust rsp by increasing 40 >>> Manually “ret” >>> >>> I am not sure if anyone has interest to re-write this function so that >>> compiler can be “fooled” again. >>> Thanks, >>> Ray >>> >>> ======================= >>> ; Function compile flags: /Ogspy >>> ; File e:\work\edk2\MdePkg\Library\BaseLib\CpuDeadLoop.c >>> ; COMDAT CpuDeadLoop >>> _TEXT SEGMENT >>> Index$ = 48 >>> CpuDeadLoop PROC >>> ; COMDAT >>> >>> ; 26 : { >>> >>> $LN12: >>> 00000 48 83 ec 28 sub rsp, 40 >>> ; 00000028H >>> >>> ; 27 : volatile UINTN Index; >>> ; 28 : >>> ; 29 : for (Index = 0; Index == 0;) { >>> >>> 00004 48 c7 44 24 30 >>> 00 00 00 00 mov QWORD PTR Index$[rsp], 0 >>> $LN10@CpuDeadLoo: >>> >>> ; 30 : CpuPause (); >>> >>> 0000d 48 8b 44 24 30 mov rax, QWORD PTR Index$[rsp] >>> 00012 e8 00 00 00 00 call CpuPause >>> 00017 eb f4 jmp SHORT $LN10@CpuDeadLoo >>> CpuDeadLoop ENDP >>> _TEXT ENDS >>> END >>> >>> >>> >> > > -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. 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