[Qemu-devel] Segmentation Fault running Raspberry Pi OS.

[Julio Faracco]

Hi guys,

I was developing a simple OS for Raspberry Pi 2.
When I was debugging my OS using "-s -S" options for QEMU, I was
getting a segfault: Segmentation fault (core dumped).

After that, I decided to run QEMU (for ARM using a raspi2 machine) inside GDB.

$ gdb ./arm-softmmu/qemu-system-arm
(gdb) run -kernel ~/myos/kernel.elf -cpu arm1176 -m 256 -M raspi2 -s -S

After starting my kernel in another GDB instance, I got a segfault as
I mentioned.
Here is the error and the backtrace:

Thread 1 "qemu-system-arm" received signal SIGSEGV, Segmentation fault.
0x0000555555785da7 in tb_page_remove (tb=0x7fffd2cf40f0, ptb=0x30) at
/home/julio/qemu/translate-all.c:1033
1033        ptb = &tb1->page_next[n1];
(gdb) bt
#0  0x0000555555785da7 in tb_page_remove (tb=0x7fffd2cf40f0, ptb=0x30)
at /home/julio/qemu/translate-all.c:1033
#1  tb_phys_invalidate (tb=0x7fffd2cf40f0,
address@hidden)
    at /home/julio/qemu/translate-all.c:1119
#2  0x0000555555786844 in tb_invalidate_phys_page_range (start=65948,
end=65949, address@hidden)
    at /home/julio/qemu/translate-all.c:1519
#3  0x0000555555786c9a in tb_invalidate_phys_addr (as=<optimized out>,
addr=<optimized out>)
    at /home/julio/qemu/translate-all.c:1714
#4  0x000055555577b13a in breakpoint_invalidate (cpu=0x7fffd2b84088,
pc=65948) at /home/julio/qemu/exec.c:704
#5  0x000055555577d8cf in cpu_breakpoint_remove_by_ref (cpu=<optimized
out>, breakpoint=0x5555570105f0)
    at /home/julio/qemu/exec.c:869
#6  0x000055555577d927 in cpu_breakpoint_remove
(address@hidden, address@hidden,
address@hidden)
    at /home/julio/qemu/exec.c:857
#7  0x00005555557bd889 in gdb_breakpoint_remove (type=<optimized out>,
len=<optimized out>, addr=65948)
    at /home/julio/qemu/gdbstub.c:717
#8  gdb_handle_packet (address@hidden,
address@hidden "z0,1019c,4")
    at /home/julio/qemu/gdbstub.c:1035
#9  0x00005555557be352 in gdb_read_byte (ch=52, s=0x55555700a000) at
/home/julio/qemu/gdbstub.c:1459
#10 gdb_chr_receive (opaque=<optimized out>, buf=<optimized out>,
size=<optimized out>) at /home/julio/qemu/gdbstub.c:1672
#11 0x00005555558cfde1 in tcp_chr_read (chan=<optimized out>,
cond=<optimized out>, opaque=0x55555700ff00) at qemu-char.c:3145
#12 0x00007fffe23e205a in g_main_context_dispatch () from
/lib/x86_64-linux-gnu/libglib-2.0.so.0
#13 0x0000555555a7c79b in glib_pollfds_poll () at main-loop.c:215
#14 os_host_main_loop_wait (timeout=<optimized out>) at main-loop.c:260
#15 main_loop_wait (nonblocking=<optimized out>) at main-loop.c:508
#16 0x0000555555776c74 in main_loop () at vl.c:1966
#17 main (argc=<optimized out>, argv=<optimized out>, envp=<optimized
out>) at vl.c:4684

I noticed that the function page_find_alloc(); sometime returns a NULL pointer.
So, the ptb pointer (tb1 = *ptb at the begining) is NULL and when the
code is trying to access the attribute "page_next", it does not work.

Can it be the cause? Please, any guidance for this issue?

Thanks!

--
Julio Cesar Faracco