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. View/Reply Online (#105048): https://edk2.groups.io/g/devel/message/105048 Mute This Topic: https://groups.io/mt/98987896/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/leave/9847357/21656/1706620634/xyzzy [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
