Re: [linus:master] [x86/bugs] 6613d82e61: general_protection_fault:#[##]

[Pawan Gupta]

On Thu, Mar 28, 2024 at 03:36:28PM +0800, kernel test robot wrote:
> compiler: clang-17
> test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G
> 
> (please refer to attached dmesg/kmsg for entire log/backtrace)
> 
> 
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> | Closes: https://lore.kernel.org/oe-lkp/202403281553.79f5a16f-lkp@xxxxxxxxx
> 
> 
> [   25.175767][  T670] VFS: Warning: trinity-c2 using old stat() call. Recompile your binary.
> [   25.245597][  T669] general protection fault: 0000 [#1] PREEMPT SMP
> [   25.246417][  T669] CPU: 1 PID: 669 Comm: trinity-c1 Not tainted 6.8.0-rc5-00004-g6613d82e617d #1 85a4928d2e6b42899c3861e57e26bdc646c4c5f9
> [   25.247743][  T669] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> [ 25.248865][ T669] EIP: restore_all_switch_stack (kbuild/src/consumer/arch/x86/entry/entry_32.S:957) 
> [ 25.249510][ T669] Code: 4c 24 10 36 89 48 fc 8b 4c 24 0c 81 e1 ff ff 00 00 36 89 48 f8 8b 4c 24 08 36 89 48 f4 8b 4c 24 04 36 89 48 f0 59 8d 60 f0 58 <0f> 00 2d 00 94 d5 c1 cf 6a 00 68 88 6b d4 c1 eb 00 fc 0f a0 50 b8
> All code
> ========
>    0:	4c 24 10             	rex.WR and $0x10,%al
>    3:	36 89 48 fc          	ss mov %ecx,-0x4(%rax)
>    7:	8b 4c 24 0c          	mov    0xc(%rsp),%ecx
>    b:	81 e1 ff ff 00 00    	and    $0xffff,%ecx
>   11:	36 89 48 f8          	ss mov %ecx,-0x8(%rax)
>   15:	8b 4c 24 08          	mov    0x8(%rsp),%ecx
>   19:	36 89 48 f4          	ss mov %ecx,-0xc(%rax)
>   1d:	8b 4c 24 04          	mov    0x4(%rsp),%ecx
>   21:	36 89 48 f0          	ss mov %ecx,-0x10(%rax)
>   25:	59                   	pop    %rcx
>   26:	8d 60 f0             	lea    -0x10(%rax),%esp
>   29:	58                   	pop    %rax
>   2a:*	0f 00 2d 00 94 d5 c1 	verw   -0x3e2a6c00(%rip)        # 0xffffffffc1d59431		<-- trapping instruction

This is due to 64-bit addressing with CONFIG_X86_32=y on clang.

I haven't tried with clang, but I don't see this happening with gcc-11:

	entry_INT80_32:
	...
	<+446>:   mov    0x4(%esp),%ecx
	<+450>:   mov    %ecx,%ss:-0x10(%eax)
	<+454>:   pop    %ecx
	<+455>:   lea    -0x10(%eax),%esp
	<+458>:   pop    %eax
	<+459>:   verw   0xc1d5c700              <----------
	<+466>:   iret

>   31:	cf                   	iret
>   32:	6a 00                	push   $0x0
>   34:	68 88 6b d4 c1       	push   $0xffffffffc1d46b88
>   39:	eb 00                	jmp    0x3b
..

The config has CONFIG_X86_32=y, but it is possible that in 32-bit build
with clang, 64-bit mode expansion of "VERW (_ASM_RIP(addr))" is getting
used i.e. __ASM_FORM_RAW(b) below:

  file: arch/x86/include/asm/asm.h
  ...
  #ifndef __x86_64__
  /* 32 bit */
  # define __ASM_SEL(a,b)         __ASM_FORM(a)
  # define __ASM_SEL_RAW(a,b)     __ASM_FORM_RAW(a)
  #else
  /* 64 bit */
  # define __ASM_SEL(a,b)         __ASM_FORM(b)
  # define __ASM_SEL_RAW(a,b)     __ASM_FORM_RAW(b)   <--------
  #endif
  ...
  /* Adds a (%rip) suffix on 64 bits only; for immediate memory references */
  #define _ASM_RIP(x)     __ASM_SEL_RAW(x, x (__ASM_REGPFX rip))

Possibly __x86_64__ is being defined with clang even when CONFIG_X86_32=y.

I am not sure about current level of 32-bit mode support in clang. This
seems inconclusive:

  https://discourse.llvm.org/t/x86-32-bit-testing/65480

Does anyone care about 32-bit mode builds with clang?