From a64afc225240b2b27129ccfb0516d7c958b98040 Mon Sep 17 00:00:00 2001 From: Florian Weimer Date: Wed, 21 Apr 2021 11:50:43 +0200 Subject: [PATCH] nptl_db: Support different libpthread/ld.so load orders (bug 27744) libthread_db is loaded once GDB encounters libpthread, and at this point, ld.so may not have been processed by GDB yet. As a result, _rtld_global cannot be accessed by regular means from libthread_db. To make this work until GDB can be fixed, acess _rtld_global through a pointer stored in libpthread. The new test does not reproduce bug 27744 with --disable-hardcoded-path-in-tests, but is still a valid smoke test. With --enable-hardcoded-path-in-tests, it is necessary to avoid add-symbol-file because this can tickle a GDB bug. Fixes commit 1daccf403b1bd86370eb94edca794dc106d02039 ("nptl: Move stack list variables into _rtld_global"). Tested-by: Emil Velikov --- nptl/Makefile | 19 +++- nptl/pthread_create.c | 8 ++ nptl/tst-pthread-gdb-attach-static.c | 1 + nptl/tst-pthread-gdb-attach.c | 143 +++++++++++++++++++++++++++ nptl_db/structs.def | 3 +- nptl_db/td_init.c | 15 +-- nptl_db/thread_dbP.h | 2 + 7 files changed, 180 insertions(+), 11 deletions(-) create mode 100644 nptl/tst-pthread-gdb-attach-static.c create mode 100644 nptl/tst-pthread-gdb-attach.c Index: glibc-2.33/nptl/Makefile =================================================================== --- glibc-2.33.orig/nptl/Makefile +++ glibc-2.33/nptl/Makefile @@ -294,7 +294,8 @@ tests = tst-attr2 tst-attr3 tst-default- tst-thread-affinity-sched \ tst-pthread-defaultattr-free \ tst-pthread-attr-sigmask \ - tst-pthread-timedlock-lockloop + tst-pthread-timedlock-lockloop \ + tst-pthread-gdb-attach tst-pthread-gdb-attach-static tests-container = tst-pthread-getattr @@ -344,6 +345,22 @@ CPPFLAGS-test-cond-printers.c := $(CFLAG CPPFLAGS-test-rwlockattr-printers.c := $(CFLAGS-printers-tests) CPPFLAGS-test-rwlock-printers.c := $(CFLAGS-printers-tests) +# Reuse the CFLAGS setting for the GDB attaching test. It needs +# debugging information. +CFLAGS-tst-pthread-gdb-attach.c := $(CFLAGS-printers-tests) +CPPFLAGS-tst-pthread-gdb-attach.c := $(CFLAGS-printers-tests) +ifeq ($(build-shared)$(build-hardcoded-path-in-tests),yesno) +CPPFLAGS-tst-pthread-gdb-attach.c += -DDO_ADD_SYMBOL_FILE=1 +else +CPPFLAGS-tst-pthread-gdb-attach.c += -DDO_ADD_SYMBOL_FILE=0 +endif +CFLAGS-tst-pthread-gdb-attach-static.c := $(CFLAGS-printers-tests) +CPPFLAGS-tst-pthread-gdb-attach-static.c := \ + $(CFLAGS-printers-tests) -DDO_ADD_SYMBOL_FILE=0 +# As of version 9.2, GDB cannot attach properly to PIE programs that +# were launched with an explicit ld.so invocation. +tst-pthread-gdb-attach-no-pie = yes + ifeq ($(build-shared),yes) tests-printers-libs := $(shared-thread-library) else @@ -415,7 +432,8 @@ link-libc-static := $(common-objpfx)libc tests-static += tst-stackguard1-static \ tst-cancel24-static \ tst-mutex8-static tst-mutexpi8-static tst-sem11-static \ - tst-sem12-static tst-cond11-static + tst-sem12-static tst-cond11-static \ + tst-pthread-gdb-attach-static tests += tst-cancel24-static Index: glibc-2.33/nptl/pthread_create.c =================================================================== --- glibc-2.33.orig/nptl/pthread_create.c +++ glibc-2.33/nptl/pthread_create.c @@ -51,6 +51,14 @@ static td_thr_events_t __nptl_threads_ev /* Pointer to descriptor with the last event. */ static struct pthread *__nptl_last_event __attribute_used__; +#ifdef SHARED +/* This variable is used to access _rtld_global from libthread_db. If + GDB loads libpthread before ld.so, it is not possible to resolve + _rtld_global directly during libpthread initialization. */ +static struct rtld_global *__nptl_rtld_global __attribute_used__ + = &_rtld_global; +#endif + /* Number of threads running. */ unsigned int __nptl_nthreads = 1; Index: glibc-2.33/nptl/tst-pthread-gdb-attach-static.c =================================================================== --- /dev/null +++ glibc-2.33/nptl/tst-pthread-gdb-attach-static.c @@ -0,0 +1 @@ +#include "tst-pthread-gdb-attach.c" Index: glibc-2.33/nptl/tst-pthread-gdb-attach.c =================================================================== --- /dev/null +++ glibc-2.33/nptl/tst-pthread-gdb-attach.c @@ -0,0 +1,217 @@ +/* Smoke testing GDB process attach with thread-local variable access. + Copyright (C) 2021 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 runs GDB against a forked copy of itself, to check + whether libthread_db can be loaded, and that access to thread-local + variables works. */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +/* Starts out as zero, changed to 1 or 2 by the debugger, depending on + the thread. */ +__thread volatile int altered_by_debugger; + +/* Common prefix between 32-bit and 64-bit ELF. */ +struct elf_prefix +{ + unsigned char e_ident[EI_NIDENT]; + uint16_t e_type; + uint16_t e_machine; + uint32_t e_version; +}; +_Static_assert (sizeof (struct elf_prefix) == EI_NIDENT + 8, + "padding in struct elf_prefix"); + +/* Reads the ELF header from PATH. Returns true if the header can be + read, false if the file is too short. */ +static bool +read_elf_header (const char *path, struct elf_prefix *elf) +{ + int fd = xopen (path, O_RDONLY, 0); + bool result = read (fd, elf, sizeof (*elf)) == sizeof (*elf); + xclose (fd); + return result; +} + +/* Searches for "gdb" alongside the path variable. See execvpe. */ +static char * +find_gdb (void) +{ + const char *path = getenv ("PATH"); + if (path == NULL) + return NULL; + while (true) + { + const char *colon = strchrnul (path, ':'); + char *candidate = xasprintf ("%.*s/gdb", (int) (colon - path), path); + if (access (candidate, X_OK) == 0) + return candidate; + free (candidate); + if (*colon == '\0') + break; + path = colon + 1; + } + return NULL; +} + +/* Writes the GDB script to run the test to PATH. */ +static void +write_gdbscript (const char *path, int tested_pid) +{ + FILE *fp = xfopen (path, "w"); + fprintf (fp, + "set trace-commands on\n" + "set debug libthread-db 1\n" +#if DO_ADD_SYMBOL_FILE + /* Do not do this unconditionally to work around a GDB + assertion failure: ../../gdb/symtab.c:6404: + internal-error: CORE_ADDR get_msymbol_address(objfile*, + const minimal_symbol*): Assertion `(objf->flags & + OBJF_MAINLINE) == 0' failed. */ + "add-symbol-file %1$s/nptl/tst-pthread-gdb-attach\n" +#endif + "set auto-load safe-path %1$s/nptl_db\n" + "set libthread-db-search-path %1$s/nptl_db\n" + "attach %2$d\n", + support_objdir_root, tested_pid); + fputs ("break debugger_inspection_point\n" + "continue\n" + "thread 1\n" + "print altered_by_debugger\n" + "print altered_by_debugger = 1\n" + "thread 2\n" + "print altered_by_debugger\n" + "print altered_by_debugger = 2\n" + "continue\n", + fp); + xfclose (fp); +} + +/* The test sets a breakpoint on this function and alters the + altered_by_debugger thread-local variable. */ +void __attribute__ ((weak)) +debugger_inspection_point (void) +{ +} + +/* Thread function for the test thread in the subprocess. */ +static void * +subprocess_thread (void *closure) +{ + /* Wait until altered_by_debugger changes the value away from 0. */ + while (altered_by_debugger == 0) + { + usleep (100 * 1000); + debugger_inspection_point (); + } + + TEST_COMPARE (altered_by_debugger, 2); + return NULL; +} + +/* This function implements the subprocess under test. It creates a + second thread, waiting for its value to change to 2, and checks + that the main thread also changed its value to 1. */ +static void +in_subprocess (void) +{ + pthread_t thr = xpthread_create (NULL, subprocess_thread, NULL); + TEST_VERIFY (xpthread_join (thr) == NULL); + TEST_COMPARE (altered_by_debugger, 1); + _exit (0); +} + +static int +do_test (void) +{ + char *gdb_path = find_gdb (); + if (gdb_path == NULL) + FAIL_UNSUPPORTED ("gdb command not found in PATH: %s", getenv ("PATH")); + + /* Check that libthread_db is compatible with the gdb architecture + because gdb loads it via dlopen. */ + { + char *threaddb_path = xasprintf ("%s/nptl_db/libthread_db.so", + support_objdir_root); + struct elf_prefix elf_threaddb; + TEST_VERIFY_EXIT (read_elf_header (threaddb_path, &elf_threaddb)); + struct elf_prefix elf_gdb; + /* If the ELF header cannot be read or "gdb" is not an ELF file, + assume this is a wrapper script that can run. */ + if (read_elf_header (gdb_path, &elf_gdb) + && memcmp (&elf_gdb, ELFMAG, SELFMAG) == 0) + { + if (elf_gdb.e_ident[EI_CLASS] != elf_threaddb.e_ident[EI_CLASS]) + FAIL_UNSUPPORTED ("GDB at %s has wrong class", gdb_path); + if (elf_gdb.e_ident[EI_DATA] != elf_threaddb.e_ident[EI_DATA]) + FAIL_UNSUPPORTED ("GDB at %s has wrong data", gdb_path); + if (elf_gdb.e_machine != elf_threaddb.e_machine) + FAIL_UNSUPPORTED ("GDB at %s has wrong machine", gdb_path); + } + free (threaddb_path); + } + + pid_t tested_pid = xfork (); + if (tested_pid == 0) + in_subprocess (); + char *tested_pid_string = xasprintf ("%d", tested_pid); + + char *gdbscript; + xclose (create_temp_file ("tst-pthread-gdb-attach-", &gdbscript)); + write_gdbscript (gdbscript, tested_pid); + + pid_t gdb_pid = xfork (); + if (gdb_pid == 0) + { + xdup2 (STDOUT_FILENO, STDERR_FILENO); + execl (gdb_path, "gdb", "-nx", "-batch", "-x", gdbscript, NULL); + if (errno == ENOENT) + _exit (EXIT_UNSUPPORTED); + else + _exit (1); + } + + int status; + TEST_COMPARE (xwaitpid (gdb_pid, &status, 0), gdb_pid); + if (WIFEXITED (status) && WEXITSTATUS (status) == EXIT_UNSUPPORTED) + /* gdb is not installed. */ + return EXIT_UNSUPPORTED; + TEST_COMPARE (status, 0); + TEST_COMPARE (xwaitpid (tested_pid, &status, 0), tested_pid); + TEST_COMPARE (status, 0); + + free (tested_pid_string); + free (gdbscript); + free (gdb_path); + return 0; +} + +#include Index: glibc-2.33/nptl_db/structs.def =================================================================== --- glibc-2.33.orig/nptl_db/structs.def +++ glibc-2.33/nptl_db/structs.def @@ -100,8 +100,7 @@ DB_STRUCT_FIELD (pthread, dtvp) #endif #if !(IS_IN (libpthread) && !defined SHARED) -DB_STRUCT (rtld_global) -DB_RTLD_VARIABLE (_rtld_global) +DB_VARIABLE (__nptl_rtld_global) #endif DB_RTLD_GLOBAL_FIELD (dl_tls_dtv_slotinfo_list) DB_RTLD_GLOBAL_FIELD (dl_stack_user) Index: glibc-2.33/nptl_db/td_init.c =================================================================== --- glibc-2.33.orig/nptl_db/td_init.c +++ glibc-2.33/nptl_db/td_init.c @@ -33,13 +33,14 @@ td_init (void) bool __td_ta_rtld_global (td_thragent_t *ta) { - if (ta->ta_addr__rtld_global == 0 - && td_mod_lookup (ta->ph, LD_SO, SYM__rtld_global, - &ta->ta_addr__rtld_global) != PS_OK) + if (ta->ta_addr__rtld_global == 0) { - ta->ta_addr__rtld_global = (void*)-1; - return false; + psaddr_t rtldglobalp; + if (DB_GET_VALUE (rtldglobalp, ta, __nptl_rtld_global, 0) == TD_OK) + ta->ta_addr__rtld_global = rtldglobalp; + else + ta->ta_addr__rtld_global = (void *) -1; } - else - return ta->ta_addr__rtld_global != (void*)-1; + + return ta->ta_addr__rtld_global != (void *)-1; } Index: glibc-2.33/nptl_db/thread_dbP.h =================================================================== --- glibc-2.33.orig/nptl_db/thread_dbP.h +++ glibc-2.33/nptl_db/thread_dbP.h @@ -108,6 +108,8 @@ struct td_thragent # undef DB_SYMBOL # undef DB_VARIABLE + psaddr_t ta_addr__rtld_global; + /* The method of locating a thread's th_unique value. */ enum {