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/* Smoke testing GDB process attach with thread-local variable access.
Copyright (C) 2021-2024 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
<https://www.gnu.org/licenses/>. */
/* 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 <elf.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <support/capture_subprocess.h>
#include <support/check.h>
#include <support/xptrace.h>
#include <support/subprocess.h>
#include <support/support.h>
#include <support/temp_file.h>
#include <support/test-driver.h>
#include <support/xstdio.h>
#include <support/xthread.h>
#include <support/xunistd.h>
#include <unistd.h>
/* 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 *arg)
{
pthread_t thr = xpthread_create (NULL, subprocess_thread, NULL);
TEST_VERIFY (xpthread_join (thr) == NULL);
TEST_COMPARE (altered_by_debugger, 1);
_exit (0);
}
static void
gdb_process (const char *gdb_path, const char *gdbscript, pid_t *tested_pid)
{
/* Create a copy of current test to check with gdb. As the
target_process is a child of this gdb_process, gdb is also able
to attach to target_process if YAMA is configured to 1 =
"restricted ptrace". */
struct support_subprocess target = support_subprocess (in_subprocess, NULL);
write_gdbscript (gdbscript, target.pid);
*tested_pid = target.pid;
xdup2 (STDOUT_FILENO, STDERR_FILENO);
execl (gdb_path, "gdb", "-nx", "-batch", "-x", gdbscript, NULL);
if (errno == ENOENT)
_exit (EXIT_UNSUPPORTED);
else
_exit (1);
}
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);
}
/* Check if our subprocess can be debugged with ptrace. */
{
int ptrace_scope = support_ptrace_scope ();
if (ptrace_scope >= 2)
FAIL_UNSUPPORTED ("/proc/sys/kernel/yama/ptrace_scope >= 2");
}
char *gdbscript;
xclose (create_temp_file ("tst-pthread-gdb-attach-", &gdbscript));
/* Run 'gdb' on test subprocess which will be created in gdb_process.
The pid of the subprocess will be written to 'tested_pid'. */
pid_t *tested_pid = support_shared_allocate (sizeof (pid_t));
pid_t gdb_pid = xfork ();
if (gdb_pid == 0)
gdb_process (gdb_path, gdbscript, tested_pid);
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);
kill (*tested_pid, SIGKILL);
support_shared_free (tested_pid);
free (gdbscript);
free (gdb_path);
return 0;
}
#include <support/test-driver.c>
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