commit d0f07f7df8d9758c838674b70144ac73bcbd1634 Author: Florian Weimer Date: Tue May 30 13:25:50 2023 +0200 elf: Make more functions available for binding during dlclose (bug 30425) Previously, after destructors for a DSO have been invoked, ld.so refused to bind against that DSO in all cases. Relax this restriction somewhat if the referencing object is itself a DSO that is being unloaded. This assumes that the symbol reference is not going to be stored anywhere. The situation in the test case can arise fairly easily with C++ and objects that are built with different optimization levels and therefore define different functions with vague linkage. Reviewed-by: Carlos O'Donell Conflicts: elf/Makefile (usual test differences, link test with -ldl) diff --git a/elf/Makefile b/elf/Makefile index 6f0f36cdfe3961e8..ebf46a297d241d8f 100644 --- a/elf/Makefile +++ b/elf/Makefile @@ -362,6 +362,7 @@ tests += \ tst-big-note \ tst-debug1 \ tst-deep1 \ + tst-dlclose-lazy \ tst-dlmodcount \ tst-dlmopen1 \ tst-dlmopen3 \ @@ -711,6 +712,8 @@ modules-names = \ tst-deep1mod2 \ tst-deep1mod3 \ tst-dlmopen1mod \ + tst-dlclose-lazy-mod1 \ + tst-dlclose-lazy-mod2 \ tst-dlmopen-dlerror-mod \ tst-dlmopen-gethostbyname-mod \ tst-dlmopen-twice-mod1 \ @@ -2707,6 +2710,12 @@ $(objpfx)tst-dlmopen-twice.out: \ $(objpfx)tst-dlmopen-twice-mod1.so \ $(objpfx)tst-dlmopen-twice-mod2.so +LDFLAGS-tst-dlclose-lazy-mod1.so = -Wl,-z,lazy,--no-as-needed +$(objpfx)tst-dlclose-lazy-mod1.so: $(objpfx)tst-dlclose-lazy-mod2.so +$(objpfx)tst-dlclose-lazy: $(libdl) +$(objpfx)tst-dlclose-lazy.out: \ + $(objpfx)tst-dlclose-lazy-mod1.so $(objpfx)tst-dlclose-lazy-mod2.so + # The object tst-nodeps1-mod.so has no explicit dependencies on libc.so. $(objpfx)tst-nodeps1-mod.so: $(objpfx)tst-nodeps1-mod.os $(LINK.o) -nostartfiles -nostdlib -shared -o $@ $^ diff --git a/elf/dl-lookup.c b/elf/dl-lookup.c index 47acd134600b44b5..9e8f14b8483f5eba 100644 --- a/elf/dl-lookup.c +++ b/elf/dl-lookup.c @@ -380,8 +380,25 @@ do_lookup_x (const char *undef_name, uint_fast32_t new_hash, if ((type_class & ELF_RTYPE_CLASS_COPY) && map->l_type == lt_executable) continue; - /* Do not look into objects which are going to be removed. */ - if (map->l_removed) + /* Do not look into objects which are going to be removed, + except when the referencing object itself is being removed. + + The second part covers the situation when an object lazily + binds to another object while running its destructor, but the + destructor of the other object has already run, so that + dlclose has set l_removed. It may not always be obvious how + to avoid such a scenario to programmers creating DSOs, + particularly if C++ vague linkage is involved and triggers + symbol interposition. + + Accepting these to-be-removed objects makes the lazy and + BIND_NOW cases more similar. (With BIND_NOW, the symbol is + resolved early, before the destructor call, so the issue does + not arise.). Behavior matches the constructor scenario: the + implementation allows binding to symbols of objects whose + constructors have not run. In fact, not doing this would be + mostly incompatible with symbol interposition. */ + if (map->l_removed && !(undef_map != NULL && undef_map->l_removed)) continue; /* Print some debugging info if wanted. */ diff --git a/elf/tst-dlclose-lazy-mod1.c b/elf/tst-dlclose-lazy-mod1.c new file mode 100644 index 0000000000000000..8439dc1925cc8b41 --- /dev/null +++ b/elf/tst-dlclose-lazy-mod1.c @@ -0,0 +1,36 @@ +/* Lazy binding during dlclose. Directly loaded module. + Copyright (C) 2023 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +/* This function is called from exported_function below. It is only + defined in this module. The weak attribute mimics how G++ + implements vague linkage for C++. */ +void __attribute__ ((weak)) +lazily_bound_exported_function (void) +{ +} + +/* Called from tst-dlclose-lazy-mod2.so. */ +void +exported_function (int call_it) +{ + if (call_it) + /* Previous to the fix this would crash when called during dlclose + since symbols from the DSO were no longer available for binding + (bug 30425) after the DSO started being closed by dlclose. */ + lazily_bound_exported_function (); +} diff --git a/elf/tst-dlclose-lazy-mod2.c b/elf/tst-dlclose-lazy-mod2.c new file mode 100644 index 0000000000000000..767f69ffdb23a685 --- /dev/null +++ b/elf/tst-dlclose-lazy-mod2.c @@ -0,0 +1,49 @@ +/* Lazy binding during dlclose. Indirectly loaded module. + Copyright (C) 2023 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +#include +#include + +void +exported_function (int ignored) +{ + /* This function is interposed from tst-dlclose-lazy-mod1.so and + thus never called. */ + abort (); +} + +static void __attribute__ ((constructor)) +init (void) +{ + puts ("info: tst-dlclose-lazy-mod2.so constructor called"); + + /* Trigger lazy binding to the definition in + tst-dlclose-lazy-mod1.so, but not for + lazily_bound_exported_function in that module. */ + exported_function (0); +} + +static void __attribute__ ((destructor)) +fini (void) +{ + puts ("info: tst-dlclose-lazy-mod2.so destructor called"); + + /* Trigger the lazily_bound_exported_function call in + exported_function in tst-dlclose-lazy-mod1.so. */ + exported_function (1); +} diff --git a/elf/tst-dlclose-lazy.c b/elf/tst-dlclose-lazy.c new file mode 100644 index 0000000000000000..976a6bb6f64fa981 --- /dev/null +++ b/elf/tst-dlclose-lazy.c @@ -0,0 +1,47 @@ +/* Test lazy binding during dlclose (bug 30425). + Copyright (C) 2023 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +/* This test re-creates a situation that can arise naturally for C++ + applications due to the use of vague linkage and differences in the + set of compiler-emitted functions. A function in + tst-dlclose-lazy-mod1.so (exported_function) interposes a function + in tst-dlclose-lazy-mod2.so. This function is called from the + destructor in tst-dlclose-lazy-mod2.so, after the destructor for + tst-dlclose-lazy-mod1.so has already completed. Prior to the fix + for bug 30425, this would lead to a lazy binding failure in + tst-dlclose-lazy-mod1.so because dlclose had already marked the DSO + as unavailable for binding (by setting l_removed). */ + +#include +#include +#include + +int +main (void) +{ + /* Load tst-dlclose-lazy-mod1.so, indirectly loading + tst-dlclose-lazy-mod2.so. */ + void *handle = xdlopen ("tst-dlclose-lazy-mod1.so", RTLD_GLOBAL | RTLD_LAZY); + + /* Invoke the destructor of tst-dlclose-lazy-mod2.so, which calls + into tst-dlclose-lazy-mod1.so after its destructor has been + called. */ + xdlclose (handle); + + return 0; +}