[Bug gdb/13987] New: jit debug interface fails attaching to pieexecutables

["rth at gcc dot gnu.org" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=13987

             Bug #: 13987
           Summary: jit debug interface fails attaching to pie executables
           Product: gdb
           Version: unknown
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gdb
        AssignedTo: unassigned@sourceware.org
        ReportedBy: rth@gcc.gnu.org
    Classification: Unclassified


It appears that when we *attach* to a pie executable, the jit load happens
before the symbols are relocated to the actual pie base address.

Test case is mainline qemu.  Run x86_64-softmmu/qemu-system-x86_64 without
arguments (a window will open booting the bios).  Three scenarios:

(1) Attach gdb to running process:

Attaching to process 28585
jit_inferior_init
Reading symbols from
/home/rth/work/qemu/bld/x86_64-softmmu/qemu-system-x86_64...done.
jit_inferior_init
jit_inferior_init, descriptor_addr = 0x637580
Unable to read JIT descriptor from remote memory!
(gdb) bt
#0  0x00007ff8df1c3403 in ?? ()
#1  0x0000000000000000 in ?? ()


(2) Running qemu directly under gdb:

GNU gdb (GDB) Fedora (7.3.50.20110722-13.fc16)
...
jit_inferior_init
Reading symbols from
/home/rth/work/qemu/bld/x86_64-softmmu/qemu-system-x86_64...done.
jit_inferior_init
jit_inferior_init, descriptor_addr = 0x637580
jit_breakpoint_re_set_internal, breakpoint_addr = 0x237290
(gdb) run
Starting program: /home/rth/work/qemu/bld/x86_64-softmmu/qemu-system-x86_64 
jit_inferior_init
jit_inferior_init
jit_inferior_init, descriptor_addr = 0x555555b8b580
jit_breakpoint_re_set_internal, breakpoint_addr = 0x55555578b290
jit_inferior_init, descriptor_addr = 0x555555b8b580
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
jit_register_code, symfile_addr = 0x555556439f70, symfile_size = 848
[New Thread 0x7fffef088700 (LWP 28666)]
[New Thread 0x7fffe6585700 (LWP 28667)]

Program received signal SIG38, Real-time event 38.
[Switching to Thread 0x7fffef088700 (LWP 28666)]
tlb_set_page (env=0x5555564415b0, vaddr=946176, paddr=946176, prot=7,
mmu_idx=0, size=<optimized out>) at /home/rth/work/qemu/qemu/exec.c:2223
2223        if (is_ram_rom(section)) {
Missing separate debuginfos, use: debuginfo-install
celt051-0.5.1.3-3.fc15.x86_64 libgcc-4.6.3-2.fc16.x86_64
spice-server-0.10.1-1.fc16.x86_64
(gdb) bt
#0  tlb_set_page (env=0x5555564415b0, vaddr=946176, paddr=946176, prot=7,
mmu_idx=0, size=<optimized out>)
    at /home/rth/work/qemu/qemu/exec.c:2223
#1  0x0000555555730264 in cpu_x86_handle_mmu_fault (env=0x5555564415b0,
addr=<optimized out>, is_write1=1, mmu_idx=0)
    at /home/rth/work/qemu/qemu/target-i386/helper.c:762
#2  0x0000555555762ebc in tlb_fill (env1=<optimized out>, addr=<optimized out>,
is_write=<optimized out>, mmu_idx=<optimized out>, retaddr=
    1073754945) at /home/rth/work/qemu/qemu/target-i386/op_helper.c:5015
#3  0x0000555555768b5c in __stb_mmu (addr=949231, val=137 '\211', mmu_idx=0) at
/home/rth/work/qemu/qemu/softmmu_template.h:305
#4  0x0000000040003342 in code_gen_buffer ()
#5  0x000055555570dce1 in cpu_x86_exec (env=0x5555564415b0) at
/home/rth/work/qemu/qemu/cpu-exec.c:565
#6  0x00005555557123ab in tcg_cpu_exec (env=0x5555564415b0) at
/home/rth/work/qemu/qemu/cpus.c:1097
#7  tcg_exec_all () at /home/rth/work/qemu/qemu/cpus.c:1129
#8  qemu_tcg_cpu_thread_fn (arg=<optimized out>) at
/home/rth/work/qemu/qemu/cpus.c:833
#9  0x00007ffff60bad90 in start_thread (arg=0x7fffef088700) at
pthread_create.c:309
#10 0x00007ffff5119f5d in clone () at
../sysdeps/unix/sysv/linux/x86_64/clone.S:115


(3) Rebuild qemu with --disable-pie and attach to running process:


Attaching to process 28679
Reading symbols from
/home/rth/work/qemu/bld/x86_64-softmmu/qemu-system-x86_64...done.
...
Loaded symbols for /usr/lib64/libXfixes.so.3
jit_inferior_init
jit_inferior_init
jit_inferior_init, descriptor_addr = 0x9e5580
jit_breakpoint_re_set_internal, breakpoint_addr = 0x5e50b0
jit_inferior_init, descriptor_addr = 0x9e5580
0x0000003ef82ea403 in select () at ../sysdeps/unix/syscall-template.S:82
82    T_PSEUDO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)
(gdb) bt 
#0  0x0000003ef82ea403 in select () at ../sysdeps/unix/syscall-template.S:82
#1  0x0000000000548ee1 in os_host_main_loop_wait (timeout=1000) at
/home/rth/work/qemu/qemu/main-loop.c:304
#2  0x000000000054903b in main_loop_wait (nonblocking=0) at
/home/rth/work/qemu/qemu/main-loop.c:486
#3  0x000000000053bfdb in main_loop () at /home/rth/work/qemu/qemu/vl.c:1555
#4  0x0000000000542b10 in main (argc=1, argv=0x7fff2a711448,
envp=0x7fff2a711458) at /home/rth/work/qemu/qemu/vl.c:3643


Note that in case (2) we re-init the jit inferior again after the program
starts at its actual address, whereas in case (1) we use the unrelocated
symbol address, which then (apparently) causes the rest of symbol resolution
to fail as well.

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