Re: [Qemu-devel] sparc-softmmu uninitialized memory read?

[Blue Swirl]

On Sat, May 5, 2012 at 3:37 PM, Andreas Färber <address@hidden> wrote:
> Hello Blue,
>
> Testing a potential AREG0 fix for ppc host by malc I got an error
> running `./sparc-softmmu/sparc-softmmu` (same with CD/kernel):
>
> qemu: fatal: Trap 0x07 while interrupts disabled, Error state
> pc: 00005e0c  npc: 00005e10
> General Registers:
> %g0-7: 00000000 00000001 babababa 00000000 00000020 07ffff08 07ffe000
> babababa
>
> Current Register Window:
> %o0-7: 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> 00000000
> %l0-7: 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> 00000000
> %i0-7: 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> 00000000
>
> Floating Point Registers:
> %f00: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> %f08: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> %f16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> %f24: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> psr: 048000c0 (icc: N--- SPE: SP-) wim: 00000001
> fsr: 00000000 y: 00000020
> Abgebrochen
>
> The 0xbabababa in %g2 and %g7 is a signature I've seen in uninitialized
> memory on openSUSE 12.1 Betas. So I ran valgrind, and the following
> caught my eye on both ppc and x86_64:
>
> ==18801== Command: ./sparc-softmmu/qemu-system-sparc
> ==18801==
> ==18801== Thread 2:
> ==18801== Conditional jump or move depends on uninitialised value(s)
> ==18801==    at 0x25C5AF: compute_all_logic (cc_helper.c:37)
> ==18801==    by 0x25C648: helper_compute_psr (cc_helper.c:470)
> ==18801==    by 0x8CD0981: ???
> ==18801==  Uninitialised value was created by a heap allocation
> ==18801==    at 0x4C27CE8: memalign (in
> /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
> ==18801==    by 0x4C27D97: posix_memalign (in
> /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
> ==18801==    by 0x1F2101: qemu_memalign (oslib-posix.c:93)
> ==18801==    by 0x1F21A9: qemu_vmalloc (oslib-posix.c:126)
> ==18801==    by 0x2665F6: qemu_ram_alloc_from_ptr (exec.c:2647)
> ==18801==    by 0x286D76: memory_region_init_ram (memory.c:954)
> ==18801==    by 0x297FFD: ram_init1 (sun4m.c:757)
> ==18801==    by 0x204DAE: qdev_init (qdev.c:151)
> ==18801==    by 0x204EEC: qdev_init_nofail (qdev.c:258)
> ==18801==    by 0x298845: ram_init.constprop.7 (sun4m.c:783)
> ==18801==    by 0x298980: sun4m_hw_init (sun4m.c:862)
> ==18801==    by 0x2994A2: ss5_init (sun4m.c:1289)
>
> This is at 8f473dd104f0937ce98523fa6f9de0bd845aebbe, and cc_helper.c:37
> is int32_t dst argument of get_NZ_icc(), which is always called with
> CC_DST, i.e. env->cc_dst.
>
> This seems to indicate that a read from uninitialized memory occurred,
> from which cc_dst is being initialized?

This should happen in target-sparc/cpu.c:45
    memset(env, 0, offsetof(CPUSPARCState, breakpoints));

cc_dst is between structure start and CPU_COMMON.

89aaf60dedbe0e6415acfe816e02b538e5c54e68 fixed a bug relating to reset recently.

>
> Any idea where that could originate from or how to further debug?
> It doesn't seem to be caused by the
> 7d21dcc84b8c07918124a9c0708694d2fb013f65 OpenBIOS r1056 update.
>
> Regards,
>
> Andreas
>
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