[Qemu-devel] valgrind errors (was: [PATCH 7/8] qemu/queue.h: simplify reverse access to QTAILQ)

[Thomas Huth]

On 2018-12-10 19:28, Paolo Bonzini wrote:
> The new definition of QTAILQ does not require passing the headname,
> remove it.

 Hi Paolo,

when running current QEMU master branch with valgrind, I get
"Conditional jump or move depends on uninitialised value" errors. I've
bisected it to your patch series here. Everything is still fine and calm
with f481ee2d5e3d77c12a4c9a7756b8c2612aad84c6 ("qemu/queue.h: typedef
QTAILQ heads"), but starting with commit
eae3eb3e185028d6e862db747e3b7397600d6762 ("qemu/queue.h: simplify
reverse access to QTAILQ"), I now get:

==14580== Thread 3:
==14580== Conditional jump or move depends on uninitialised value(s)
==14580==    at 0x40C267: tcg_reg_alloc (tcg.c:3123)
==14580==    by 0x40F8FB: tcg_reg_alloc_op (tcg.c:3506)
==14580==    by 0x40F8FB: tcg_gen_code (tcg.c:3948)
==14580==    by 0x47FAFF: tb_gen_code (translate-all.c:1748)
==14580==    by 0x47E153: tb_find (cpu-exec.c:404)
==14580==    by 0x47E153: cpu_exec (cpu-exec.c:724)
==14580==    by 0x43D981: tcg_cpu_exec (cpus.c:1429)
==14580==    by 0x43FB4F: qemu_tcg_cpu_thread_fn (cpus.c:1733)
==14580==    by 0x879075: qemu_thread_start (qemu-thread-posix.c:502)
==14580==    by 0xB528DD4: start_thread (in /usr/lib64/libpthread-2.17.so)
==14580==    by 0xB83BB3C: clone (in /usr/lib64/libc-2.17.so)

Unfortunately, the commits in between do not compile, so I can not
determine the exact commit that introduced the problem, but it
definitely seems to happen due to your queue rework. Could you please
have a look?

 Thanks,
  Thomas