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

[Eli Zaretskii]

> 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?