Re: report a segment fault bug of systemtap

[maliubiao <maliubiao at gmail dot com>]

more information:

I wrote a gdb script to trace this problem, and found this
.....
die_name 0x7ffff4367e63 "objs/ngx_modules.c"
cu_name 0x21eed88 "ngx_modules.c"
die_name 0x7ffff4367e86 "elf-init.c"
cu_name 0x21eed88 "ngx_modules.c"
die_name 0x7ffff43101b3 "../sysdeps/x86_64/crtn.S"
cu_name 0x21eed88 "ngx_modules.c"
die_name 0x0
cu_name 0x21eed88 "ngx_modules.c
then segment fault

dwarf_diename(cudie) returns a null pointer

SCRIPT:
import gdb
parse_and_eval = gdb.parse_and_eval
class dwarf_query_segv(gdb.Breakpoint):
    def __init__(self):
        super(dwarf_query_segv, self).__init__(
                spec="tapsets.cxx:4192",
                type = gdb.WP_READ,
                wp_class = gdb.BP_READ_WATCHPOINT
                )
    def stop(self):
        die_name = parse_and_eval("die_name")
        cu_name = parse_and_eval("q->e.cu_name.c_str()")
        print "die_name", str(die_name)
        print "cu_name", str(cu_name)
dwarf_query_segv()

2013/12/28 maliubiao <maliubiao@gmail.com>:
> SCRIPT :
>
> global c = 0;
> probe process("/data/project/c/nginx-build/sbin/nginx").function("ngx_worker_process_cycle")
> {
>     if (c < 1) {
>         printf("%s\n", user_string($cycle->hostname->data))
>         c += 1
>     }
> }
>
> probe process("/data/project/c/nginx-build/sbin/nginx").function("ngx_epoll_process_events*")
> {
>     /* iter over array ngx_modules */
>     for (i=0; i < 512; i++) {
>         index = @var("ngx_modules@ngx_modules.c")[i]->index
>         if (index != i) {
>             break
>         }
>         ngx_modules = @var("ngx_modules@ngx_modules.c")[i]
>         ctx = @cast(ngx_modules, "ngx_module_s")->ctx
>         name = @cast(ctx, "ngx_core_module_t")->name->data
>         if (name) {
>             printf("index: %s\n", i, user_string(name));
>         }
>     }
> }
>
> STACK TRACE:
>
> Pass 1: parsed user script and 100 library script(s) using
> 89752virt/29968res/2480shr/28316data kb, in 150usr/10sys/26180real ms.
>
> Program received signal SIGSEGV, Segmentation fault.
> 0x00007ffff777e946 in __strcmp_sse42 () from /lib64/libc.so.6
> (gdb) bt
> #0  0x00007ffff777e946 in __strcmp_sse42 () from /lib64/libc.so.6
> #1  0x00000000004d57ad in dwarf_atvar_query::atvar_query_cu (cudie=0x24028a0,
>     data=0x7fffffffba80) at tapsets.cxx:4192
> #2  0x000000000054a862 in dwflpp::iterate_over_cus (this=<optimized out>,
>     callback=0x4d5760 <dwarf_atvar_query::atvar_query_cu(Dwarf_Die*, void*)>,
>     data=0x7fffffffba80, want_types=false) at dwflpp.cxx:466
> #3  0x00000000004b48cd in query_module (mod=<optimized out>,
>     name=<optimized out>, addr=4194304, arg=0x7fffffffba80) at tapsets.cxx:2132
> #4  0x00007ffff71edfa2 in dwfl_getmodules (dwfl=0x228cd60,
>     callback=0x4b4770 <query_module(Dwfl_Module*, void**, char const*,
> Dwarf_Addr, void*)>, arg=0x7fffffffba80, offset=0)
>     at ../.././elfutils-0.157/libdwfl/dwfl_getmodules.c:82
> #5  0x00000000004ca254 in dwarf_atvar_expanding_visitor::visit_atvar_op (
>     this=0x2284b40, e=0x23c4030) at tapsets.cxx:4296
> #6  0x0000000000453fb3 in update_visitor::require<expression> (this=0x2284b40,
>     src=<optimized out>, clearok=false) at staptree.h:970
> #7  0x00000000004c8e2b in replace<expression> (clearok=false,
>     src=@0x23c3d88: 0x23c4030, this=0x2284b40) at staptree.h:992
> #8  var_expanding_visitor::rewrite_lvalue (this=this@entry=0x2284b40,
>     tok=0x21eeaf0, eop="=", lvalue=@0x23c3d78: 0x23c3da0,
>     rvalue=@0x23c3d88: 0x23c4030) at tapsets.cxx:2354
> #9  0x00000000004c9369 in var_expanding_visitor::visit_assignment (
>     this=0x2284b40, e=0x23c3d60) at tapsets.cxx:2400
> ---Type <return> to continue, or q <return> to quit---
> #10 0x000000000044e1df in assignment::visit (this=0x23c3d60, u=0x2284b40)
>     at staptree.cxx:1469
> #11 0x0000000000453fb3 in update_visitor::require<expression> (this=0x2284b40,
>     src=<optimized out>, clearok=false) at staptree.h:970
> #12 0x000000000044c587 in replace<expression> (clearok=false,
>     src=<optimized out>, this=0x2284b40) at staptree.h:992
> #13 update_visitor::visit_expr_statement (this=0x2284b40, s=0x23c3d40)
>     at staptree.cxx:2599
> #14 0x000000000044a5bf in require<statement> (clearok=false,
>     src=<optimized out>, this=0x2284b40) at staptree.h:970
> #15 replace<statement> (clearok=false, src=@0x23c3d00: 0x23c3d40,
>     this=0x2284b40) at staptree.h:992
> #16 update_visitor::visit_block (this=0x2284b40, s=0x23c3cd0)
>     at staptree.cxx:2571
> #17 0x0000000000453af3 in update_visitor::require<statement> (this=0x2284b40,
>     src=<optimized out>, clearok=false) at staptree.h:970
> #18 0x000000000044cd8d in replace<statement> (clearok=false,
>     src=@0x23c37b8: 0x23c3cd0, this=0x2284b40) at staptree.h:992
> #19 update_visitor::visit_for_loop (this=0x2284b40, s=0x23c3790)
>     at staptree.cxx:2618
> #20 0x000000000044a5bf in require<statement> (clearok=false,
>     src=<optimized out>, this=0x2284b40) at staptree.h:970
> #21 replace<statement> (clearok=false, src=@0x23c3ab0: 0x23c3790,
> ---Type <return> to continue, or q <return> to quit---
>     this=0x2284b40) at staptree.h:992
> #22 update_visitor::visit_block (this=0x2284b40, s=0x23c3be0)
>     at staptree.cxx:2571
> #23 0x000000000045fba3 in require<statement> (clearok=false,
>     src=<optimized out>, this=0x2284b40) at staptree.h:970
> #24 replace<statement> (clearok=false, src=@0x23c3870: 0x23c3be0,
>     this=0x2284b40) at staptree.h:992
> #25 semantic_pass_symbols (s=...) at elaborate.cxx:1643
> #26 0x000000000046c71c in semantic_pass (s=...) at elaborate.cxx:1985
> #27 0x0000000000413c10 in passes_0_4 (s=...) at main.cxx:744
> #28 0x000000000040c97b in main (argc=<optimized out>, argv=<optimized out>)
>     at main.cxx:1101
>
> ENV:
> stap --version
> Systemtap translator/driver (version 2.4/0.157, commit
> release-2.3-131-g1acfc03 + changes)
> uname -a
> Linux linux-6pwq.site 3.11.1-1.16-desktop+ #2 SMP PREEMPT Sun Oct 6
> 11:07:07 CST 2013 x86_64 x86_64 x86_64 GNU/Linux
>
> any idea ?