[edk2-devel] ovmf miscompiles with gcc-12

[joeyli via groups.io]

Hi all, 

I have filed this issue on tianocore bugzilla:

Bug 3934 - ovmf miscompiles with gcc-12
https://bugzilla.tianocore.org/show_bug.cgi?id=3934

Thanks
Joey Lee

On Thu, May 19, 2022 at 07:43:12AM +0200, Jiri Slaby via groups.io wrote:
> Hi,
> 
> we discovered that qemu-ovmf-x86_64 doesn't start when compiled using
> gcc-12. Originally reported as:
> https://bugzilla.suse.com/show_bug.cgi?id=1199597
> 
> I run qemu as:
> qemu-kvm -drive file=/dev/null,format=raw -drive
> if=pflash,format=raw,unit=0,readonly=on,file=OVMF.fd -m 3000
> 
> The platform repeatedly resets after TemporaryRamMigration as can be seen in
> the debuglog:
> https://bugzilla.suse.com/attachment.cgi?id=858969
> 
> The reason is TemporaryRamMigration() overwrites rbp unconditionally -- it
> adds an offset to rbp even if rbp is NOT used as a frame pointer
> (-fomit-frame-pointer was always used for compilation here). So commenting
> out:
> > //JumpBuffer.Rbp = JumpBuffer.Rbp + DebugAgentContext.StackMigrateOffset;
> 
> makes it all work again. Also marking TemporaryRamMigration() as:
> __attribute__((optimize("-fno-omit-frame-pointer")))
> works around the problem too. (But that doesn't guarantee anything.)
> 
> The code is:
> >   if (SetJump (&JumpBuffer) == 0) {
> >  #if defined (MDE_CPU_IA32)
> >     JumpBuffer.Esp = JumpBuffer.Esp + DebugAgentContext.StackMigrateOffset;
> >     JumpBuffer.Ebp = JumpBuffer.Ebp + DebugAgentContext.StackMigrateOffset;
> >  #endif
> >  #if defined (MDE_CPU_X64)
> >     JumpBuffer.Rsp = JumpBuffer.Rsp + DebugAgentContext.StackMigrateOffset;
> >     JumpBuffer.Rbp = JumpBuffer.Rbp + DebugAgentContext.StackMigrateOffset;
> >  #endif
> >     LongJump (&JumpBuffer, (UINTN)-1);
> >   }
> 
> It was only coincidence this ever worked -- gcc-11 omits the frame pointer
> too, but apparently the caller (PeiCheckAndSwitchStack) does not use rbp.
> 
> PeiCheckAndSwitchStack() (gcc-12):
> 
> >     79a6:       4c 29 fd                sub    %r15,%rbp <------ used rbp
> >     79a9:       4d 29 fe                sub    %r15,%r14
> >     79ac:       48 83 ec 20             sub    $0x20,%rsp
> >     79b0:       4d 89 e0                mov    %r12,%r8
> >     79b3:       48 8d 4b 08             lea    0x8(%rbx),%rcx
> >     79b7:       48 8b 44 24 50          mov    0x50(%rsp),%rax
> >     79bc:       48 8b 54 24 20          mov    0x20(%rsp),%rdx
> >     79c1:       4d 29 e8                sub    %r13,%r8
> >     79c4:       4c 8b 4c 24 30          mov    0x30(%rsp),%r9
> >     79c9:       ff 10                   call   *(%rax)  <----------- call to TemporaryRamMigration
> >     79cb:       48 83 c4 20             add    $0x20,%rsp
> >     79cf:       be 01 00 00 00          mov    $0x1,%esi
> >     79d4:       4c 89 f7                mov    %r14,%rdi
> >     79d7:       e8 f4 a8 ff ff          call   22d0 <MigrateMemoryPages>
> >     79dc:       48 83 ec 20             sub    $0x20,%rsp
> >     79e0:       4d 89 f0                mov    %r14,%r8
> >     79e3:       31 d2                   xor    %edx,%edx
> >     79e5:       48 89 e9                mov    %rbp,%rcx   <------ rbp used
> 
> gcc-11 seems to copy rbp to r8 first and operates on r8 there instead.
> 
> Now, what is the right way to fix this? Do the SetJump/LongJump in assembly
> and wrap it into push rbp/pop rbp?
> 
> thanks,
> -- 
> js
> suse labs
> 
> 
> 
> 



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