Re: changed dlopen flags in dynlib.c, gccemacs crash

[Andrea Corallo]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: hx <silent2600@gmail.com>
>> Date: Sat, 11 Dec 2021 10:29:33 +0800
>> Cc: Andrea Corallo <akrl@sdf.org>, emacs-devel <emacs-devel@gnu.org>
>> 
>> git diff
>> diff --git a/src/comp.c b/src/comp.c
>> index 43feac6..2941f84 100644
>> --- a/src/comp.c
>> +++ b/src/comp.c
>> @@ -5191,6 +5191,8 @@ DEFUN ("comp--register-lambda", Fcomp__register_lambda,
>> Scomp__register_lambda,
>>     Lisp_Object maxarg, Lisp_Object type, Lisp_Object rest,
>>     Lisp_Object comp_u)
>>  {
>> +  CHECK_CONS(rest);
>> +
>>    Lisp_Object doc_idx = FIRST (rest);
>>    Lisp_Object intspec = SECOND (rest);
>>    struct Lisp_Native_Comp_Unit *cu = XNATIVE_COMP_UNIT (comp_u);
>> diff --git a/src/dynlib.c b/src/dynlib.c
>> index a8c8843..362530b 100644
>> --- a/src/dynlib.c
>> +++ b/src/dynlib.c
>> @@ -270,7 +270,8 @@ dynlib_close (dynlib_handle_ptr h)
>>  dynlib_handle_ptr
>>  dynlib_open (const char *path)
>>  {
>> -  return dlopen (path, RTLD_LAZY);
>> +  // return dlopen (path, RTLD_LAZY);
>> +  return dlopen (path, RTLD_LAZY|RTLD_GLOBAL);
>>  }
>>  
>> 
>> delete the eln-cache, execute with -nw -q in gdb, wait a few seconds:
>> (gdb) bt
>> #0  _dl_lookup_symbol_x (undef_name=0x555555e3814300 <error: Cannot access 
>> memory at address
>> 0x555555e3814300>, undef_map=0x555556059380, ref=0x7fffffffc1b8, 
>> symbol_scope=0x555556059718,
>> version=0x0, type_class=0, flags=2, skip_map=0x0) at dl-lookup.c:842
>> #1  0x00007ffff4082b74 in do_sym (handle=<optimized out>, 
>> name=0x555555e3814300 <error: Cannot
>> access memory at address 0x555555e3814300>, who=0x55555580b073 
>> <dynlib_sym+35>,
>> vers=vers@entry=0x0, flags=flags@entry=2) at dl-sym.c:165
>> #2  0x00007ffff408305d in _dl_sym (handle=<optimized out>, name=<optimized 
>> out>, who=<optimized out>)
>> at dl-sym.c:274
>> #3  0x00007ffff5bdf3b4 in dlsym_doit (a=a@entry=0x7fffffffc3f0) at dlsym.c:50
>> #4  0x00007ffff4083260 in __GI__dl_catch_exception 
>> (exception=exception@entry=0x7fffffffc390,
>> operate=0x7ffff5bdf3a0 <dlsym_doit>, args=0x7fffffffc3f0) at 
>> dl-error-skeleton.c:208
>> #5  0x00007ffff408331f in __GI__dl_catch_error (objname=0x555555dab830, 
>> errstring=0x555555dab838,
>> mallocedp=0x555555dab828, operate=<optimized out>, args=<optimized out>) at 
>> dl-error-skeleton.c:227
>> #6  0x00007ffff5bdfa65 in _dlerror_run (operate=operate@entry=0x7ffff5bdf3a0 
>> <dlsym_doit>,
>> args=args@entry=0x7fffffffc3f0) at dlerror.c:170
>> #7  0x00007ffff5bdf41c in __dlsym (handle=<optimized out>, name=<optimized 
>> out>) at dlsym.c:70
>> #8  0x000055555580b073 in dynlib_sym (h=0x555556059380, sym=0x555555e3814300 
>> <error: Cannot
>> access memory at address 0x555555e3814300>) at dynlib.c:280
>> #9  0x0000555555809f63 in make_subr (symbol_name=0x555555e38153, 
>> minarg=0x16, maxarg=0x16,
>> c_name=0x555555e38153, type=0xfc30, doc_idx=0xba, intspec=0x0, 
>> comp_u=0x555555df6d1d) at
>> comp.c:5147
>> #10 0x000055555580a156 in Fcomp__register_lambda (reloc_idx=0xa, 
>> c_name=0x555555e38153,
>> minarg=0x16, maxarg=0x16, type=0xfc30, rest=0x555555e17c03, 
>> comp_u=0x555555df6d1d) at comp.c:5203
>> #11 0x00007fffef0eed34 in late_top_level_run () at
>> /home/silent/.emacs.d/eln-cache/28.0.90-8dcada16/cconv-3b1f1f98-cca24f72.eln
>
> So I think this is a manifestation of the issue that Andrea was
> talking about: the way we produce native code is incompatible with
> RTLD_GLOBAL.
>
> So at this point, I think this bug report should be treated as
> "wishlist", i.e. a feature request: to support RTLD_GLOBAL in dynlib
> with native-comp.  Andrea, is that feasible, and if so, what would it
> entail?

Hi Eli,

yes, I think once we have verified the issue is what we suspect we could
dlopen eln files as before and have RTLD_GLOBAL added for the other
cases.

I'll have a look into next week and report on the feature request.

Thanks

  Andrea