[Qemu-devel] [Bug 1248168] [NEW] MIPS, self-modifying code and uncached memory

[Nikita Kanunnikov]

Public bug reported:

Self-modifying code does not work properly in MIPS in uncached and
unmapped kseg1 memory region.

For example, when running this code I get unexpected behavior:

   0:   e3000010        b       0x390
   4:   00000000        nop
        ...
 380:   00701f40        mfc0    ra,c0_epc
 384:   0400e0bb        swr     zero,4(ra)
 388:   18000042        eret
 38c:   00000000        nop
 390:   25500000        move    t2,zero
 394:   02000b34        li      t3,0x2
 398:   23504b01        subu    t2,t2,t3
 39c:   e9003c0b        j       0xcf003a4
 3a0:   0a004a21        addi    t2,t2,10
 3a4:   ffff0010        b       0x3a4
 3a8:   00000000        nop
 3ac:   00000000        nop

  I expect that swr instruction in line 384 would change `addi  t2,t2,1`0 to 
`nop`
This should work because no cache is used for this memory region.

** Affects: qemu
     Importance: Undecided
         Status: New

-- 
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1248168

Title:
  MIPS, self-modifying code and uncached memory

Status in QEMU:
  New

Bug description:
  Self-modifying code does not work properly in MIPS in uncached and
  unmapped kseg1 memory region.

  For example, when running this code I get unexpected behavior:

     0: e3000010        b       0x390
     4: 00000000        nop
        ...
   380: 00701f40        mfc0    ra,c0_epc
   384: 0400e0bb        swr     zero,4(ra)
   388: 18000042        eret
   38c: 00000000        nop
   390: 25500000        move    t2,zero
   394: 02000b34        li      t3,0x2
   398: 23504b01        subu    t2,t2,t3
   39c: e9003c0b        j       0xcf003a4
   3a0: 0a004a21        addi    t2,t2,10
   3a4: ffff0010        b       0x3a4
   3a8: 00000000        nop
   3ac: 00000000        nop

    I expect that swr instruction in line 384 would change `addi        
t2,t2,1`0 to `nop`
  This should work because no cache is used for this memory region.

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1248168/+subscriptions