From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from rn-mailsvcp-ppex-lapp14.apple.com (rn-mailsvcp-ppex-lapp14.apple.com [17.179.253.33]) by mx.groups.io with SMTP id smtpd.web09.12654.1658871530949467318 for ; Tue, 26 Jul 2022 14:38:51 -0700 Authentication-Results: mx.groups.io; dkim=pass header.i=@apple.com header.s=20180706 header.b=qyAb3qsY; spf=pass (domain: apple.com, ip: 17.179.253.33, mailfrom: afish@apple.com) Received: from pps.filterd (rn-mailsvcp-ppex-lapp14.rno.apple.com [127.0.0.1]) by rn-mailsvcp-ppex-lapp14.rno.apple.com (8.16.1.2/8.16.1.2) with SMTP id 26QLZXGi014827; Tue, 26 Jul 2022 14:38:50 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=apple.com; h=from : message-id : content-type : mime-version : subject : date : in-reply-to : cc : to : references; s=20180706; bh=R+u8zu0yLA6dZDQ4JmLY5t7XXi8jOz7vPzJaUQIR6vs=; b=qyAb3qsYuwBkXvDvmAWkO6f7zX6Nkr3t0uR3AYqzvwKHuheGFzgYLLkZ5TdcYS1eizKj bc2ueNfAGz2+B9U7UlBwifCATYdI7EOuuseAhWmnP2AayWhYZbpt2YRbTtNHFC5xDt0P Qu5TUxX9X7o1+N3IAg0a27dYwSl6ksa6XFq76WJIsqwiw0B2IsFlJfjrAPYaV2SevBl4 bcd+JXTwkhRqlfGkskEd7pwbA/J38KTU/fwk/ZQ1hrfwecQmc8f4cUuhTVmEymoULzyx JEXKfdTVcqTOIErxXOLC3hQtSRrxp+A4kP8ziUD3y99wnhZQdahSP6dtQgDnflR3LpIs ag== Received: from rn-mailsvcp-mta-lapp01.rno.apple.com (rn-mailsvcp-mta-lapp01.rno.apple.com [10.225.203.149]) by rn-mailsvcp-ppex-lapp14.rno.apple.com with ESMTP id 3hgdvap85k-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NO); Tue, 26 Jul 2022 14:38:50 -0700 Received: from rn-mailsvcp-mmp-lapp02.rno.apple.com (rn-mailsvcp-mmp-lapp02.rno.apple.com [17.179.253.15]) by rn-mailsvcp-mta-lapp01.rno.apple.com (Oracle Communications Messaging Server 8.1.0.18.20220407 64bit (built Apr 7 2022)) with ESMTPS id <0RFN00A0ZDGQ2KE0@rn-mailsvcp-mta-lapp01.rno.apple.com>; Tue, 26 Jul 2022 14:38:50 -0700 (PDT) Received: from process_milters-daemon.rn-mailsvcp-mmp-lapp02.rno.apple.com by rn-mailsvcp-mmp-lapp02.rno.apple.com (Oracle Communications Messaging Server 8.1.0.18.20220407 64bit (built Apr 7 2022)) id <0RFN00D00DFKWF00@rn-mailsvcp-mmp-lapp02.rno.apple.com>; Tue, 26 Jul 2022 14:38:50 -0700 (PDT) X-Va-A: X-Va-T-CD: 42bcc3738539b68059edd2bc024c3397 X-Va-E-CD: fa9e1aa2e33b303a80c7290ebbbc84ef X-Va-R-CD: b22de2176895e5e0422f5f3b61053f8b X-Va-CD: 0 X-Va-ID: 8b9f4ce7-a7ca-4fbf-997d-8665d01aa4f7 X-V-A: X-V-T-CD: 42bcc3738539b68059edd2bc024c3397 X-V-E-CD: fa9e1aa2e33b303a80c7290ebbbc84ef X-V-R-CD: b22de2176895e5e0422f5f3b61053f8b X-V-CD: 0 X-V-ID: ec970992-0c0e-46c0-9328-95f89d178f37 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.517,18.0.883 definitions=2022-07-26_07:2022-07-26,2022-07-26 signatures=0 Received: from smtpclient.apple (unknown [17.235.33.95]) by rn-mailsvcp-mmp-lapp02.rno.apple.com (Oracle Communications Messaging Server 8.1.0.18.20220407 64bit (built Apr 7 2022)) with ESMTPSA id <0RFN00OG2DG3Q200@rn-mailsvcp-mmp-lapp02.rno.apple.com>; Tue, 26 Jul 2022 14:38:31 -0700 (PDT) From: "Andrew Fish" Message-id: <6824753D-9F86-400C-ACCE-683A50C29F48@apple.com> MIME-version: 1.0 (Mac OS X Mail 16.0 \(3729.0.22.1.1\)) Subject: Re: [edk2-devel] Casting i128 into f64 in UEFI Rust pagefaults Date: Tue, 26 Jul 2022 14:38:16 -0700 In-reply-to: <7be4fe49-1fd3-f2cb-bf53-a471bc945718@gmail.com> Cc: Mike Kinney , "mikuback@linux.microsoft.com" , "Gaibusab, Jabeena B" , "Yao, Jiewen" To: edk2-devel-groups-io , ayushdevel1325@gmail.com References: <15b0ac38-4b55-4b19-3f76-506c5b858949@gmail.com> <170523E2507C1293.4676@groups.io> <116DE63D-B96C-4D2F-9CF6-299F053329D7@apple.com> <57E4EE5B-4A4C-4592-A811-14DB025C58E1@apple.com> <17a84748-381f-e438-a338-c6ab0dbabdc6@gmail.com> <47BEA05F-B1E1-4BCC-B281-E596AD9B5781@apple.com> <7be4fe49-1fd3-f2cb-bf53-a471bc945718@gmail.com> X-Mailer: Apple Mail (2.3729.0.22.1.1) X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.517,18.0.883 definitions=2022-07-26_07:2022-07-26,2022-07-26 signatures=0 Content-type: multipart/alternative; boundary="Apple-Mail=_2E242AA4-B78A-463B-89C0-BAD73FA066B6" --Apple-Mail=_2E242AA4-B78A-463B-89C0-BAD73FA066B6 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 Ayush, Well bugs in the runtime are a classic case when have good debugging infras= tructure pays off and that class of issue is what started this email thread= .=20 It is not hard to try out gdb to see what happens if you are using QEMU.=20 >>From the root of the edk2 repo: $ OvmfPkg/build.sh qemu -gdb tcp::9000 Then from another terminal=20 $ cd BaseTools/Scripts $ gdb -ex "target remote localhost:9000" -ex "source efi_gdb.py" That should get you a symbolicated stack frame.=20 The QEMU -gdb works like a JTAG debugger. You can put dead loops in your co= de, let it run, and then attach.=20 Thanks, Andrew Fish > On Jul 26, 2022, at 12:15 PM, Ayush Singh wrot= e: >=20 > Hi Andrew. I do agree with having better debugging support for Rust-UEFI.= However, I am not much experienced with even the C side of UEFI debugging,= so it has been difficult for me to do much on the Rust side either. It isn= 't like Rust UEFI debugging is not possible. There are some examples ([1]),= but as you might guess, they are quite few. Additionally, most of them see= m to be concentrated around Windows. Finally, there is actually quite good = debugging support in uefi-rs [2], but well, that's licensed under MPL-2.0, = so I have stayed clear of it. >=20 >=20 >=20 > Another reason I have gone so long without using any actual debugger is b= ecause, well, Rust makes it quite explicit where wired errors can occur. Mo= st functions, even inside the std, don't use pointers but rather use `NonNu= ll`, `MaybeUninint` or some other safe abstraction. Even on the worst failu= re, the program will abort instead of crash. On aborting, Rust also gives a= nice message on stderr stating exactly where the error occurred along with= all the details of the error. Basically, it was always so clear what cause= d the error and where it occurred that I simply didn't feel the need to att= ach a debugger, till now. >=20 >=20 >=20 > There is some work going on to actually document using Rust for UEFI in t= he rustc docs, sponsored by Red Hat [3], so the situation should improve so= on. What I do know is that the `.pdb` files generated by Rust (which are al= ways generated) should contain all the symbols for debugging. I can work on= debugging once I finish up with solving all other errors which are due to = my implementation of std rather than the ones that have been caused by the = rust intrinsic. >=20 >=20 >=20 > Ayush Singh >=20 >=20 >=20 > [1]: https://xitan.me/posts/rust-uefi-runtime-driver/ >=20 > [2]: https://github.com/rust-osdev/uefi-rs >=20 > [3]: https://github.com/rust-lang/rust/pull/99760 >=20 >=20 >=20 > On 7/26/22 23:20, Andrew Fish wrote: >>> On Jul 25, 2022, at 10:43 PM, Ayush Singh wrote: >>>=20 >>> Hi Andrew. Thanks for all your work. The more I look at this, the more = it feels like it might be a problem on the LLVM side instead of Rust. I als= o found some more tests (all related to numbers btw) which can cause differ= ent types of exceptions, so I think I will try filing bugs upstream.=20 >>>=20 >>=20 >> Ayush, >>=20 >> In general If we want to move to Rust we are going to need a way to debu= g issues like this down to the root cause. I think figuring out how to debu= g will make it easier to move forward with the Rust port in general. It wil= l time well spent.=20 >>=20 >> The best way to get LLVM fixed, if it is even broken, is to provide a si= mple test case that reproduces the behavior. I don=E2=80=99t think at this = point we know what is going on. It is very unlikely that some random LLVM d= eveloper is going to invest the time in trying to setup some UEFI environme= nt to try and root cause this bug. I general find I have to create a simple= at desk example and then I get stuff fixed quickly. Basically a test case = the LLVM developer can compile at their desk and see the error in assembler= , or at least run it at desk and have bogus output.=20 >>=20 >> I=E2=80=99m not 100% sure what toolchain you are using. Can you `objdump= -d hello_world_std.efi`and get some symbols with the disassembly? For VC++= I think it would be `DUMPBIN /DISASM`. >>=20 >> What are you planning on using for source level debugging Rust? I wrote = some gdb[1] and lldb[2] debugging commands in Python. I=E2=80=99m guessing = loading Rust symbols from PE/COFF images should be similar, as long as the = debugger knows about rust.=20 >>=20 >> I=E2=80=99m happy to help you figure out stuff related to debugging Rust= .=20 >>=20 >> [1] https://github.com/tianocore/edk2/blob/master/BaseTools/Scripts/efi_= gdb.py >> [2] https://github.com/tianocore/edk2/blob/master/BaseTools/Scripts/efi_= lldb.py >>=20 >> Thanks, >>=20 >> Andrew Fish >>=20 >>> Yours Sincerely, >>>=20 >>> Ayush Singh >>>=20 >>>=20 >>>=20 >>> On 7/26/22 00:24, Andrew Fish wrote: >>>> I guess I could at least dump to the end (req)=E2=80=A6. Going backwar= ds is a bit painful in x86.=20 >>>>=20 >>>> (lldb) dis -s 0x0000000140001B60 -b -c 30 >>>> hello_world_std.efi[0x140001b60]: 48 8b 09 movq = (%rcx), %rcx >>>> hello_world_std.efi[0x140001b63]: 48 01 c1 addq = %rax, %rcx >>>> hello_world_std.efi[0x140001b66]: 4c 89 c2 movq = %r8, %rdx >>>> hello_world_std.efi[0x140001b69]: 48 11 c2 adcq = %rax, %rdx >>>> hello_world_std.efi[0x140001b6c]: 48 31 c1 xorq = %rax, %rcx >>>> hello_world_std.efi[0x140001b6f]: 48 31 c2 xorq = %rax, %rdx >>>> hello_world_std.efi[0x140001b72]: 48 be 00 00 00 00 00 00 00 80 movab= sq $-0x8000000000000000, %rsi ; imm =3D 0x8000000000000000=20 >>>> hello_world_std.efi[0x140001b7c]: 4c 21 c6 andq = %r8, %rsi >>>> hello_world_std.efi[0x140001b7f]: e8 5c 55 00 00 callq= 0x1400070e0 >>>> hello_world_std.efi[0x140001b84]: 48 09 f0 orq = %rsi, %rax >>>> hello_world_std.efi[0x140001b87]: 48 83 c4 20 addq = $0x20, %rsp >>>> hello_world_std.efi[0x140001b8b]: 5e popq = %rsi >>>> hello_world_std.efi[0x140001b8c]: c3 retq = =20 >>>> hello_world_std.efi[0x140001b8d]: cc int3 = =20 >>>> hello_world_std.efi[0x140001b8e]: cc int3 = =20 >>>> hello_world_std.efi[0x140001b8f]: cc int3 = =20 >>>> hello_world_std.efi[0x140001b90]: e9 db 55 00 00 jmp = 0x140007170 >>>> hello_world_std.efi[0x140001b95]: cc int3 = =20 >>>> =E2=80=A6 >>>>=20 >>>> Then we can guess based on how functions get aligned to find the start= =E2=80=A6. >>>>=20 >>>> hello_world_std.efi[0x140001b50]: 56 = pushq %rsi >>>> hello_world_std.efi[0x140001b51]: 48 83 ec 20 = subq $0x20, %rsp >>>> hello_world_std.efi[0x140001b55]: 4c 8b 41 08 = movq 0x8(%rcx), %r8 >>>> hello_world_std.efi[0x140001b59]: 4c 89 c0 = movq %r8, %rax >>>> hello_world_std.efi[0x140001b5c]: 48 c1 f8 3f = sarq $0x3f, %rax >>>> hello_world_std.efi[0x140001b60]: 48 8b 09 = movq (%rcx), %rcx >>>> hello_world_std.efi[0x140001b63]: 48 01 c1 = addq %rax, %rcx >>>> hello_world_std.efi[0x140001b66]: 4c 89 c2 = movq %r8, %rdx >>>> hello_world_std.efi[0x140001b69]: 48 11 c2 = adcq %rax, %rdx >>>> hello_world_std.efi[0x140001b6c]: 48 31 c1 = xorq %rax, %rcx >>>> hello_world_std.efi[0x140001b6f]: 48 31 c2 = xorq %rax, %rdx >>>> hello_world_std.efi[0x140001b72]: 48 be 00 00 00 00 00 00 00 80 = movabsq $-0x8000000000000000, %rsi ; imm =3D 0x8000000000000000=20 >>>> hello_world_std.efi[0x140001b7c]: 4c 21 c6 = andq %r8, %rsi >>>> hello_world_std.efi[0x140001b7f]: e8 5c 55 00 00 = callq 0x1400070e0 >>>> hello_world_std.efi[0x140001b84]: 48 09 f0 = orq %rsi, %rax >>>> hello_world_std.efi[0x140001b87]: 48 83 c4 20 = addq $0x20, %rsp >>>> hello_world_std.efi[0x140001b8b]: 5e = popq %rsi >>>> hello_world_std.efi[0x140001b8c]: c3 = retq =20 >>>>=20 >>>> So the faulting function is getting passed a bad pointer as its 1st ar= g.=20 >>>>=20 >>>> Thanks, >>>>=20 >>>> Andrew Fish >>>>=20 >>>>> On Jul 25, 2022, at 11:45 AM, Andrew Fish wrote: >>>>>=20 >>>>> Ops=E2=80=A6 Looks like your PE/COFF is linked at 0x0000000140000000,= so 0x140001b60 is the interesting bit. >>>>>=20 >>>>> (lldb) dis -s 0x0000000140001B60 -b >>>>> hello_world_std.efi[0x140001b60]: 48 8b 09 movq= (%rcx), %rcx >>>>> hello_world_std.efi[0x140001b63]: 48 01 c1 addq= %rax, %rcx >>>>> hello_world_std.efi[0x140001b66]: 4c 89 c2 movq= %r8, %rdx >>>>> hello_world_std.efi[0x140001b69]: 48 11 c2 adcq= %rax, %rdx >>>>> hello_world_std.efi[0x140001b6c]: 48 31 c1 xorq= %rax, %rcx >>>>> hello_world_std.efi[0x140001b6f]: 48 31 c2 xorq= %rax, %rdx >>>>> hello_world_std.efi[0x140001b72]: 48 be 00 00 00 00 00 00 00 80 mova= bsq $-0x8000000000000000, %rsi ; imm =3D 0x8000000000000000=20 >>>>> hello_world_std.efi[0x140001b7c]: 4c 21 c6 andq= %r8, %rsi >>>>>=20 >>>>> RCX - FFFFFFFFFFFFFFFF >>>>>=20 >>>>> So yea that looks like the fault.=20 >>>>>=20 >>>>> I don=E2=80=99t see that pattern in your .s file=E2=80=A6.=20 >>>>>=20 >>>>> Can you figure out what function is @ 0x140001b60 in the PE/COFF imag= e. Do you have a map file from the linker? >>>>>=20 >>>>> Thanks, >>>>>=20 >>>>> Andrew Fish >>>>>=20 >>>>> PS Again sorry I don=E2=80=99t have anything installed to crack PDB f= iles.=20 >>>>>=20 >>>>> Thanks, >>>>>=20 >>>>> Andrew Fish >>>>>=20 >>>>>> On Jul 25, 2022, at 10:51 AM, Andrew Fish via groups.io wrote: >>>>>>=20 >>>>>> Ayush, >>>>>>=20 >>>>>> CR2 is the fault address so 0xFFFFFFFFFFFFFFFF. Given for EFI Virt = =3D=3D Physical the fault address looks like a bad pointer.=20 >>>>>>=20 >>>>>> Sorry I=E2=80=99ve not used VC++ in a long time so I don=E2=80=99t k= now how to debug with VC++, but If I was using clang/lldb I=E2=80=99d look = at the source and assembly for the fault address.=20 >>>>>>=20 >>>>>> The image base is: 0x000000000603C000 >>>>>> The fault PC/RIP is: 000000000603DB60 >>>>>>=20 >>>>>> So the faulting code is at 0x1B60 in the image. Given the images are= linked at zero you should be able to load the build product into the debug= ger and look at what code is at offset 0x1B60. The same should work for any= tools that dump the binary.=20 >>>>>>=20 >>>>>> Thanks, >>>>>>=20 >>>>>> Andrew Fish >>>>>>=20 >>>>>>> On Jul 25, 2022, at 10:33 AM, Ayush Singh wrote: >>>>>>>=20 >>>>>>> Hello everyone.While running Rust tests in UEFI environment, I have= come across a numeric test that causes a pagefault. A simple reproducible = example for this is given below: >>>>>>>=20 >>>>>>> ```rust >>>>>>>=20 >>>>>>> fn main() { >>>>>>> use std::hint::black_box as b; >>>>>>>=20 >>>>>>> let z: i128 =3D b(1); >>>>>>> assert!((-z as f64) < 0.0); >>>>>>> } >>>>>>>=20 >>>>>>> ``` >>>>>>>=20 >>>>>>>=20 >>>>>>> The exception output is as follows: >>>>>>>=20 >>>>>>> ``` >>>>>>>=20 >>>>>>> !!!! X64 Exception Type - 0E(#PF - Page-Fault) CPU Apic ID - 00000= 000 !!!! >>>>>>> ExceptionData - 0000000000000000 I:0 R:0 U:0 W:0= P:0 PK:0 SS:0 SGX:0 >>>>>>> RIP - 000000000603DB60, CS - 0000000000000038, RFLAGS - 000000000= 0000246 >>>>>>> RAX - 0000000000000000, RCX - FFFFFFFFFFFFFFFF, RDX - FFFFFFFFFFFF= FFFF >>>>>>> RBX - 0000000000000000, RSP - 0000000007EDF1D0, RBP - 0000000007ED= F4C0 >>>>>>> RSI - 0000000007EDF360, RDI - 0000000007EDF3C0 >>>>>>> R8 - 0000000000000000, R9 - 0000000000000038, R10 - 000000000000= 0000 >>>>>>> R11 - 0000000000000000, R12 - 00000000060C6018, R13 - 0000000007ED= F520 >>>>>>> R14 - 0000000007EDF6A8, R15 - 0000000005FA9490 >>>>>>> DS - 0000000000000030, ES - 0000000000000030, FS - 000000000000= 0030 >>>>>>> GS - 0000000000000030, SS - 0000000000000030 >>>>>>> CR0 - 0000000080010033, CR2 - FFFFFFFFFFFFFFFF, CR3 - 0000000007C0= 1000 >>>>>>> CR4 - 0000000000000668, CR8 - 0000000000000000 >>>>>>> DR0 - 0000000000000000, DR1 - 0000000000000000, DR2 - 000000000000= 0000 >>>>>>> DR3 - 0000000000000000, DR6 - 00000000FFFF0FF0, DR7 - 000000000000= 0400 >>>>>>> GDTR - 00000000079DE000 0000000000000047, LDTR - 0000000000000000 >>>>>>> IDTR - 0000000007418018 0000000000000FFF, TR - 0000000000000000 >>>>>>> FXSAVE_STATE - 0000000007EDEE30 >>>>>>> !!!! Find image based on IP(0x603DB60) /var/home/ayush/Documents/Pr= ogramming/Rust/uefi/hello_world_std/target/x86_64-unknown-uefi/debug/deps/h= ello_world_std-338028f9369e2d42.pdb (ImageBase=3D000000000603C000, EntryPoi= nt=3D000000000603D8C0) !!!! >>>>>>>=20 >>>>>>> ``` >>>>>>>=20 >>>>>>>=20 >>>>>>> From my testing, the exception only occurs when a few conditions ar= e met. >>>>>>>=20 >>>>>>> 1. The binary is compiled in Debug mode. No error in Release mode. >>>>>>>=20 >>>>>>> 2. `i128` is in a black_box [1]. Does not occur if `black_box` is n= ot present. >>>>>>>=20 >>>>>>> 3. It has to be `i128`. `i64` or something else work fine. >>>>>>>=20 >>>>>>> 4. The cast has to be done on `-z`. Doing the same with `+z` is fin= e. >>>>>>>=20 >>>>>>>=20 >>>>>>> I have also been discussing this in the Rust zulipchat [2], so feel= free to chime in there. >>>>>>>=20 >>>>>>>=20 >>>>>>> Additionally, here are links for more information about this progra= m: >>>>>>>=20 >>>>>>> 1. Assembly: https://rust-lang.zulipchat.com/user_uploads/4715/od51= Y9Dkfjahcg9HHcOud8Fm/hello_world_std-338028f9369e2d42.s >>>>>>>=20 >>>>>>> 2. EFI Binary: https://rust-lang.zulipchat.com/user_uploads/4715/Ck= nqtXLR8SaJZmyOnXctQkpL/hello_world_std.efi >>>>>>>=20 >>>>>>> 3. PDB file: https://rust-lang.zulipchat.com/user_uploads/4715/zV4i= 6DsjgQXotp_gS1naEsU0/hello_world_std-338028f9369e2d42.pdb >>>>>>>=20 >>>>>>>=20 >>>>>>> Yours Sincerely, >>>>>>>=20 >>>>>>> Ayush Singh >>>>>>>=20 >>>>>>>=20 >>>>>>> [1]: https://doc.rust-lang.org/std/hint/fn.black_box.html >>>>>>>=20 >>>>>>> [2]: https://rust-lang.zulipchat.com/#narrow/stream/182449-t-compil= er.2Fhelp/topic/Casting.20i128.20to.20f64.20in.20black_box.20causes.20excep= tion.20in.20UEFI >>>>>>>=20 >>>>>>>=20 >>>>>>>=20 >>>>>>=20 >>>>>=20 >>>>=20 >>=20 >=20 >=20 --Apple-Mail=_2E242AA4-B78A-463B-89C0-BAD73FA066B6 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=utf-8 Ayush,


Well bugs in the runtime are a classic case when have good debuggin= g infrastructure pays off and that class of issue is what started this emai= l thread. 

It is not hard to try out gdb to s= ee what happens if you are using QEMU. 
From the root of the= edk2 repo:
$ OvmfPkg/build.sh qemu = -gdb tcp::9000

Then from another terminal =
$ cd BaseTools/Scripts
$  gdb -ex "target remote localhost:9000" -ex "source efi_gdb.= py"

That should get you a symbolicated stac= k frame. 

The QEMU -gdb works like a JTAG deb= ugger. You can put dead loops in your code, let it run, and then attach.&nb= sp;

Thanks,

Andrew Fish

On Jul 26, 2022, at 12:15 PM, Ayu= sh Singh <ayushdevel1325@gmail.com> wrote:

=20 =20

Hi Andrew. I do agree with having better debugging support for Rust-UEFI. However, I am not much experienced with even the C side of UEFI debugging, so it has been difficult for me to do much on the Rust side either. It isn't like Rust UEFI debugging is not possible. There are some examples ([1]), but as you might guess, they are quite few. Additionally, most of them seem to be concentrated around Windows. Finally, there is actually quite good debugging support in uefi-rs [2], but well, that's licensed under MPL-2.0, so I have stayed clear of it.


Another reason I have gone so long without using any actual debugger is because, well, Rust makes it quite explicit where wired errors can occur. Most functions, even inside the std, don't use pointers but rather use `NonNull`, `MaybeUninint` or some other safe abstraction. Even on the worst failure, the program will abort instead of crash. On aborting, Rust also gives a nice message on stderr stating exactly where the error occurred along with all the details of the error. Basically, it was always so clear what caused the error and where it occurred that I simply didn't feel the need to attach a debugger, till now.


There is some work going on to actually document using Rust for UEFI in the rustc docs, sponsored by Red Hat [3], so the situation should improve soon. What I do know is that the `.pdb` files generated by Rust (which are always generated) should contain all the symbols for debugging. I can work on debugging once I finish up with solving all other errors which are due to my implementation of std rather than the ones that have been caused by the rust intrinsic.


Ayush Singh


[1]: https://xitan.me/posts/rust-uefi-runtime-= driver/

[2]: https://github.com/rust-osdev/uefi-rs

=

[3]: https://github.com/rust-lang/rust/pull/99760


On 7/26/22 23:20, Andrew Fish wrote:
On Jul 25, 2022, at 10:43 PM, Ayush Singh <ayushdevel1325@gmail.com> wrote:

Hi Andrew. Thanks for all your work. The more I look at this, the more it feels like it might be a problem on the LLVM side instead of Rust. I also found some more tests (all related to numbers btw) which can cause different types of exceptions, so I think I will try filing bugs upstream.


Ayush,

In general If we want to move to Rust we are going to need a way to debug issues like this down to the root cause. I think figuring out how to debug will make it easier to move forward with the Rust port in general. It will time well spent. 

The best way to get LLVM fixed, if it is even broken, is to provide a simple test case that reproduces the behavior. I don=E2=80=99t think at this point we know what is going on. I= t is very unlikely that some random LLVM developer is going to invest the time in trying to setup some UEFI environment to try and root cause this bug. I general find I have to create a simple at desk example and then I get stuff fixed quickly. Basically a test case the LLVM developer can compile at their desk and see the error in assembler, or at least run it at desk and have bogus output. 

I=E2=80=99m not 100% sure what toolchain you are using. Can = you `objdump -d hello_world_std.efi`and get some symbols with the disassembly? For VC++ I think it would be `DUMPBIN /DISASM`.

What are you planning on using for source level debugging Rust? I wrote some gdb[1] and lldb[2] debugging commands in Python. I=E2=80=99m guessing loading Rust symbols from PE/COFF images should be similar, as long as the debugger knows about rust. 

I=E2=80=99m happy to help you figure out stuff related to debugging Rust. 


Thanks,

Andrew Fish

Yours Sincerely,

Ayush Singh


On 7/26/22 00:24, Andrew Fish wrote:
I guess I could at least dump to the end (req)=E2=80=A6. Go= ing backwards is a bit painful in x86. 

(lldb) dis -s 0x0000000140001B60 -b -c 30
hello_world_std.efi[0x140001b60]= : 48 8b 09             &n= bsp;         movq   (%rcx), %rcx
hello_world_std.efi[0x140001b63]= : 48 01 c1             &n= bsp;         addq   %rax, %rcx
hello_world_std.efi[0x140001b66]= : 4c 89 c2             &n= bsp;         movq   %r8, %rdx
hello_world_std.efi[0x140001b69]= : 48 11 c2             &n= bsp;         adcq   %rax, %rdx
hello_world_std.efi[0x140001b6c]= : 48 31 c1             &n= bsp;         xorq   %rax, %rcx
hello_world_std.efi[0x140001b6f]= : 48 31 c2             &n= bsp;         xorq   %rax, %rdx
hello_world_std.efi[0x140001b72]= : 48 be 00 00 00 00 00 00 00 80  movabsq $-0x8000000000000000, %rsi ; imm =3D 0x8000000000000000 
hello_world_std.efi[0x140001b7c]= : 4c 21 c6             &n= bsp;         andq   %r8, %rsi
hello_world_std.efi[0x140001b7f]= : e8 5c 55 00 00           &nb= sp;     callq  0x1400070e0
hello_world_std.efi[0x140001b84]= : 48 09 f0             &n= bsp;         orq    %rsi, %rax
hello_world_std.efi[0x140001b87]= : 48 83 c4 20            =         addq   $0x20, %rsp
hello_world_std.efi[0x140001b8b]= : 5e               &= nbsp;             popq   %rsi
hello_world_std.efi[0x140001b8c]= : c3               &= nbsp;             retq   
hello_world_std.efi[0x140001b8d]= : cc               &= nbsp;             int3   
hello_world_std.efi[0x140001b8e]= : cc               &= nbsp;             int3   
hello_world_std.efi[0x140001b8f]= : cc               &= nbsp;             int3   
hello_world_std.efi[0x140001b90]= : e9 db 55 00 00           &nb= sp;     jmp    0x140007170
hello_world_std.efi[0x140001b95]= : cc               &= nbsp;             int3   
=E2=80=A6

Then we can guess based on how functions get aligned to find the start=E2=80=A6.=

hello_world_std.efi[0x140001= b50]: 56             &nbs= p;                     pu= shq  %rsi
hello_world_std.efi[0x140001= b51]: 48 83 ec 20          &nb= sp;               subq   $0x20, %rsp
hello_world_std.efi[0x140001= b55]: 4c 8b 41 08          &nb= sp;               movq   0x8(%rcx), %r8
hello_world_std.efi[0x140001= b59]: 4c 89 c0            = ;                 movq   %r8, %rax
hello_world_std.efi[0x140001= b5c]: 48 c1 f8 3f          &nb= sp;               sarq   $0x3f, %rax
hello_world_std.efi[0x140001= b60]: 48 8b 09            = ;                 movq   (%rcx), %rcx
hello_world_std.efi[0x140001= b63]: 48 01 c1            = ;                 addq   %rax, %rcx
hello_world_std.efi[0x140001= b66]: 4c 89 c2            = ;                 movq   %r8, %rdx
hello_world_std.efi[0x140001= b69]: 48 11 c2            = ;                 adcq   %rax, %rdx
hello_world_std.efi[0x140001= b6c]: 48 31 c1            = ;                 xorq   %rax, %rcx
hello_world_std.efi[0x140001= b6f]: 48 31 c2            = ;                 xorq   %rax, %rdx
hello_world_std.efi[0x140001= b72]: 48 be 00 00 00 00 00 00 00 80     =   movabsq $-0x8000000000000000, %rsi ; imm =3D 0x8000000000000000 
hello_world_std.efi[0x140001= b7c]: 4c 21 c6            = ;                 andq   %r8, %rsi
hello_world_std.efi[0x140001= b7f]: e8 5c 55 00 00          =             callq  0x1400070e0
hello_world_std.efi[0x140001= b84]: 48 09 f0            = ;                 orq    %rsi, %rax
hello_world_std.efi[0x140001= b87]: 48 83 c4 20          &nb= sp;               addq   $0x20, %rsp
hello_world_std.efi[0x140001= b8b]: 5e             &nbs= p;                     po= pq   %rsi
hello_world_std.efi[0x140001= b8c]: c3             &nbs= p;                     re= tq   

So the faulting function is getting passed a bad pointer as its 1st arg. 

Thanks,

Andrew Fish

On Jul 25, 2022, at 11:45 AM, Andrew Fish <afish@apple.com> wrote:

Ops=E2=80=A6 Looks like your PE/COFF is linked at 0x0000000140000000, so 0x140001b60 is the interesting bit.

(lldb) dis -s 0x0000000140001B60 -b
hello_world_std.efi[0x= 140001b60]: 48 8b 09          =             movq   (%rcx), %rcx
hello_world_std.efi[0x= 140001b63]: 48 01 c1          =             addq   %rax, %rcx
hello_world_std.efi[0x= 140001b66]: 4c 89 c2          =             movq   %r8, %rdx
hello_world_std.efi[0x= 140001b69]: 48 11 c2          =             adcq   %rax, %rdx
hello_world_std.efi[0x= 140001b6c]: 48 31 c1          =             xorq   %rax, %rcx
hello_world_std.efi[0x= 140001b6f]: 48 31 c2          =             xorq   %rax, %rdx
hello_world_std.efi[0x= 140001b72]: 48 be 00 00 00 00 00 00 00 80  movabsq $-0x8000000000000000, %rsi ; imm =3D 0x8000000000000000 
hello_world_std.efi[0x= 140001b7c]: 4c 21 c6          =             andq   %r8, %rsi

 RCX - FFFFFFFFFFFFFFFF

So yea that looks like the fault. 

I don=E2=80=99t see th= at pattern in your .s file=E2=80=A6. 

Can you figure out what function is @ 0x140001b60 in the PE/COFF image. Do you have a map file from the linker?

Thanks,

Andrew Fish

PS Again sorry I don=E2=80=99t have anything installed to cr= ack PDB files. 

Thanks,

Andrew Fish

On Jul 25, 2022, at 10:51 AM, Andrew Fish via groups.io <afish=3Dapple.com@groups.io> wrote:

Ayush,

CR2 is the fault address so 0xFFFFFFFFFFFFFFFF. Given for EFI Virt =3D=3D Physical the fault address looks like a bad pointer. 

Sorry I=E2=80= =99ve not used VC++ in a long time so I don=E2=80=99t know how to debug with VC= ++, but If I was using clang/lldb I=E2=80= =99d look at the source and assembly for the fault address. 

The image base is: 0x000000000603C000
The fault PC/RIP is: 000000000603DB60

So the faulting code is at 0x1B60 in the image. Given the images are linked at zero you should be able to load the build product into the debugger and look at what code is at offset 0x1B60. The same should work for any tools that dump the binary. 

Thanks,

Andrew Fish

On Jul 25, 2022, at 10:33 AM, Ayush Singh <ayushdevel1325@gmail.com> wrote:

Hello everyone.While running Rust tests in UEFI environment, I have come across a numeric test that causes a pagefault. A simple reproducible example for this is given below:

```rust

fn main() {=
   = use std::hint::black_box as b;

   = let z: i128 =3D b(1);
   = assert!((-z as f64) < 0.0);
}

```


The exception output is as follows:
```

!!!! X64 Exception Type - 0E(#PF - Page-Fault)  CPU Apic ID - 00000000 !!!!
ExceptionData - 0000000000000000  I:0 R:0 U:0 W:0 P:0 PK:0 SS:0 SGX:0
RIP  - 000000000603DB60, CS  - 0000000000000038, RFLAGS - 0000000000000246
RAX  - 0000000000000000, RCX - FFFFFFFFFFFFFFFF, RDX - FFFFFFFFFFFFFFFF
RBX  - 0000000000000000, RSP - 0000000007EDF1D0, RBP - 0000000007EDF4C0
RSI  - 0000000007EDF360, RDI - 0000000007EDF3C0
R8   - 0000000000000000, R9  - 0000000000000038, R10 - 0000000000000000
R11  - 0000000000000000, R12 - 00000000060C6018, R13 - 0000000007EDF520
R14  - 0000000007EDF6A8, R15 - 0000000005FA9490
DS   - 0000000000000030, ES  - 0000000000000030, FS  - 0000000000000030
GS   - 0000000000000030, SS  - 0000000000000030
CR0  - 0000000080010033, CR2 - FFFFFFFFFFFFFFFF, CR3 - 0000000007C01000
CR4  - 0000000000000668, CR8 - 0000000000000000
DR0  - 0000000000000000, DR1 - 0000000000000000, DR2 - 0000000000000000
DR3  - 0000000000000000, DR6 - 00000000FFFF0FF0, DR7 - 0000000000000400
GDTR - 00000000079DE000 0000000000000047, LDTR - 0000000000000000
IDTR - 0000000007418018 0000000000000FFF,   T= R - 0000000000000000
FXSAVE_STATE - 0000000007EDEE30
!!!! Find image based on IP(0x603DB60) /var/home/ayush/Documents/Programming/Rust/uefi/hello_world_std/target/x86_= 64-unknown-uefi/debug/deps/hello_world_std-338028f9369e2d42.pdb (ImageBase=3D000000000603C000, EntryPoint=3D000000000603D8C0) !!!!

```


From my testing, the exception only occurs when a few conditions are met.

1. The binary is compiled in Debug mode. No error in Release mode.

2. `i128` is in a black_box [1]. Does not occur if `black_box` is not present.

3. It has to be `i128`. `i64` or something else work fine.

4. The cast has to be done on `-z`. Doing the same with `+z` is fine.


I have also been discussing this in the Rust zulipchat [2], so feel free to chime in there.<= br style=3D"caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;">

Additionally, here are links for more information about this program:

1. Assembly: https://rust-lang.zulipchat.com/user_upload= s/4715/od51Y9Dkfjahcg9HHcOud8Fm/hello_world_std-338028f9369e2d42.s

2. EFI Binary: https://rust-lang.zulipchat.com/user_upload= s/4715/CknqtXLR8SaJZmyOnXctQkpL/hello_world_std.efi

3. PDB file: https://rust-lang.zulipchat.com/user_upload= s/4715/zV4i6DsjgQXotp_gS1naEsU0/hello_world_std-338028f9369e2d42.pdb

Yours Sincerely,

Ayush Singh=


[1]: https://doc.rust-lang.org/std/hint/fn.black= _box.html

[2]: https://rust-lang.zulipchat.com/#narrow/str= eam/182449-t-compiler.2Fhelp/topic/Casting.20i128.20to.20f64.20in.20black_b= ox.20causes.20exception.20in.20UEFI




=20



=20

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