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7ae1a6a6cc
On Linux, we need to explicitly ptrace attach to all lwps of a process. Because GDB might not be connected yet when an attach is requested, and thus it may not be possible to activate thread_db, as that requires access to symbols (IOW, gdbserver --attach), a while ago we make linux_attach loop over the lwps as listed by /proc/PID/task to find the lwps to attach to. linux_attach_lwp_1 has: ... if (initial) /* If lwp is the tgid, we handle adding existing threads later. Otherwise we just add lwp without bothering about any other threads. */ ptid = ptid_build (lwpid, lwpid, 0); else { /* Note that extracting the pid from the current inferior is safe, since we're always called in the context of the same process as this new thread. */ int pid = pid_of (current_inferior); ptid = ptid_build (pid, lwpid, 0); } That "safe" comment referred to linux_attach_lwp being called by thread-db.c. But this was clearly missed when a new call to linux_attach_lwp_1 was added to linux_attach. As a result, current_inferior will be set to some random process, and non-initial lwps of the second inferior get assigned the pid of the wrong inferior. E.g., in the case of attaching to two inferiors, for the second inferior (and so on), non-initial lwps of the second inferior get assigned the pid of the first inferior. This doesn't trigger on the first inferior, when current_inferior is NULL, add_thread switches the current inferior to the newly added thread. Rather than making linux_attach switch current_inferior temporarily (thus avoiding further reliance on global state), or making linux_attach_lwp_1 get the tgid from /proc, which add extra syscalls, and will be wrong in case of the user having originally attached directly to a non-tgid lwp, and then that lwp spawning new clones (the ptid.pid field of further new clones should be the same as the original lwp's pid, which is not the tgid), we note that callers of linux_attach_lwp/linux_attach_lwp_1 always have the right pid handy already, so they can pass it down along with the lwpid. The only other reason for the "initial" parameter is to error out instead of warn in case of attach failure, when we're first attaching to a process. There are only three callers of linux_attach_lwp/linux_attach_lwp_1, and each wants to print a different warn/error string, so we can just move the error/warn out of linux_attach_lwp_1 to the callers, thus getting rid of the "initial" parameter. There really nothing gdbserver-specific about attaching to two threaded processes, so this adds a new test under gdb.multi/. The test passes cleanly against the native GNU/Linux target, but fails/triggers the bug against GDBserver (before the patch), with the native-extended-remote board (as plain remote doesn't support multi-process). Tested on x86_64 Fedora 17, with the native-extended-gdbserver board. gdb/gdbserver/ 2014-04-25 Pedro Alves <palves@redhat.com> PR server/16255 * linux-low.c (linux_attach_fail_reason_string): New function. (linux_attach_lwp): Delete. (linux_attach_lwp_1): Rename to ... (linux_attach_lwp): ... this. Take a ptid instead of a pid as argument. Remove "initial" parameter. Return int instead of void. Don't error or warn here. (linux_attach): Adjust to call linux_attach_lwp. Call error on failure to attach to the tgid. Call warning when failing to attach to an lwp. * linux-low.h (linux_attach_lwp): Take a ptid instead of a pid as argument. Remove "initial" parameter. Return int instead of void. Don't error or warn here. (linux_attach_fail_reason_string): New declaration. * thread-db.c (attach_thread): Adjust to linux_attach_lwp's interface change. Use linux_attach_fail_reason_string. gdb/ 2014-04-25 Pedro Alves <palves@redhat.com> PR server/16255 * common/linux-ptrace.c (linux_ptrace_attach_warnings): Rename to ... (linux_ptrace_attach_fail_reason): ... this. Remove "warning: " and newline from built string. * common/linux-ptrace.h (linux_ptrace_attach_warnings): Rename to ... (linux_ptrace_attach_fail_reason): ... this. * linux-nat.c (linux_nat_attach): Adjust to use linux_ptrace_attach_fail_reason. gdb/testsuite/ 2014-04-25 Simon Marchi <simon.marchi@ericsson.com> Pedro Alves <palves@redhat.com> PR server/16255 * gdb.multi/multi-attach.c: New file. * gdb.multi/multi-attach.exp: New file.
545 lines
16 KiB
C
545 lines
16 KiB
C
/* Linux-specific ptrace manipulation routines.
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Copyright (C) 2012-2014 Free Software Foundation, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#ifdef GDBSERVER
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#include "server.h"
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#else
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#include "defs.h"
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#include <string.h>
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#endif
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#include "linux-ptrace.h"
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#include "linux-procfs.h"
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#include "nat/linux-waitpid.h"
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#include "buffer.h"
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#include "gdb_assert.h"
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#include "gdb_wait.h"
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#include <stdint.h>
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/* Stores the currently supported ptrace options. A value of
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-1 means we did not check for features yet. A value of 0 means
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there are no supported features. */
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static int current_ptrace_options = -1;
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/* Find all possible reasons we could fail to attach PID and append
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these as strings to the already initialized BUFFER. '\0'
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termination of BUFFER must be done by the caller. */
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void
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linux_ptrace_attach_fail_reason (pid_t pid, struct buffer *buffer)
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{
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pid_t tracerpid;
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tracerpid = linux_proc_get_tracerpid (pid);
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if (tracerpid > 0)
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buffer_xml_printf (buffer, _("process %d is already traced "
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"by process %d"),
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(int) pid, (int) tracerpid);
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if (linux_proc_pid_is_zombie (pid))
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buffer_xml_printf (buffer, _("process %d is a zombie "
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"- the process has already terminated"),
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(int) pid);
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}
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#if defined __i386__ || defined __x86_64__
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/* Address of the 'ret' instruction in asm code block below. */
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extern void (linux_ptrace_test_ret_to_nx_instr) (void);
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#include <sys/reg.h>
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#include <sys/mman.h>
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#include <signal.h>
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#endif /* defined __i386__ || defined __x86_64__ */
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/* Test broken off-trunk Linux kernel patchset for NX support on i386. It was
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removed in Fedora kernel 88fa1f0332d188795ed73d7ac2b1564e11a0b4cd.
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Test also x86_64 arch for PaX support. */
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static void
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linux_ptrace_test_ret_to_nx (void)
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{
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#if defined __i386__ || defined __x86_64__
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pid_t child, got_pid;
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gdb_byte *return_address, *pc;
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long l;
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int status, kill_status;
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return_address = mmap (NULL, 2, PROT_READ | PROT_WRITE,
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MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
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if (return_address == MAP_FAILED)
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{
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warning (_("linux_ptrace_test_ret_to_nx: Cannot mmap: %s"),
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strerror (errno));
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return;
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}
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/* Put there 'int3'. */
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*return_address = 0xcc;
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child = fork ();
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switch (child)
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{
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case -1:
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warning (_("linux_ptrace_test_ret_to_nx: Cannot fork: %s"),
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strerror (errno));
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return;
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case 0:
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l = ptrace (PTRACE_TRACEME, 0, (PTRACE_TYPE_ARG3) NULL,
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(PTRACE_TYPE_ARG4) NULL);
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if (l != 0)
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warning (_("linux_ptrace_test_ret_to_nx: Cannot PTRACE_TRACEME: %s"),
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strerror (errno));
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else
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{
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#if defined __i386__
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asm volatile ("pushl %0;"
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".globl linux_ptrace_test_ret_to_nx_instr;"
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"linux_ptrace_test_ret_to_nx_instr:"
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"ret"
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: : "r" (return_address) : "%esp", "memory");
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#elif defined __x86_64__
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asm volatile ("pushq %0;"
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".globl linux_ptrace_test_ret_to_nx_instr;"
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"linux_ptrace_test_ret_to_nx_instr:"
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"ret"
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: : "r" ((uint64_t) (uintptr_t) return_address)
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: "%rsp", "memory");
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#else
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# error "!__i386__ && !__x86_64__"
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#endif
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gdb_assert_not_reached ("asm block did not terminate");
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}
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_exit (1);
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}
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errno = 0;
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got_pid = waitpid (child, &status, 0);
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if (got_pid != child)
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{
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warning (_("linux_ptrace_test_ret_to_nx: waitpid returned %ld: %s"),
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(long) got_pid, strerror (errno));
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return;
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}
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if (WIFSIGNALED (status))
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{
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if (WTERMSIG (status) != SIGKILL)
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warning (_("linux_ptrace_test_ret_to_nx: WTERMSIG %d is not SIGKILL!"),
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(int) WTERMSIG (status));
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else
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warning (_("Cannot call inferior functions, Linux kernel PaX "
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"protection forbids return to non-executable pages!"));
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return;
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}
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if (!WIFSTOPPED (status))
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{
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warning (_("linux_ptrace_test_ret_to_nx: status %d is not WIFSTOPPED!"),
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status);
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return;
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}
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/* We may get SIGSEGV due to missing PROT_EXEC of the return_address. */
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if (WSTOPSIG (status) != SIGTRAP && WSTOPSIG (status) != SIGSEGV)
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{
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warning (_("linux_ptrace_test_ret_to_nx: "
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"WSTOPSIG %d is neither SIGTRAP nor SIGSEGV!"),
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(int) WSTOPSIG (status));
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return;
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}
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errno = 0;
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#if defined __i386__
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l = ptrace (PTRACE_PEEKUSER, child, (PTRACE_TYPE_ARG3) (uintptr_t) (EIP * 4),
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(PTRACE_TYPE_ARG4) NULL);
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#elif defined __x86_64__
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l = ptrace (PTRACE_PEEKUSER, child, (PTRACE_TYPE_ARG3) (uintptr_t) (RIP * 8),
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(PTRACE_TYPE_ARG4) NULL);
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#else
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# error "!__i386__ && !__x86_64__"
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#endif
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if (errno != 0)
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{
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warning (_("linux_ptrace_test_ret_to_nx: Cannot PTRACE_PEEKUSER: %s"),
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strerror (errno));
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return;
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}
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pc = (void *) (uintptr_t) l;
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kill (child, SIGKILL);
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ptrace (PTRACE_KILL, child, (PTRACE_TYPE_ARG3) NULL,
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(PTRACE_TYPE_ARG4) NULL);
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errno = 0;
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got_pid = waitpid (child, &kill_status, 0);
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if (got_pid != child)
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{
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warning (_("linux_ptrace_test_ret_to_nx: "
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"PTRACE_KILL waitpid returned %ld: %s"),
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(long) got_pid, strerror (errno));
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return;
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}
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if (!WIFSIGNALED (kill_status))
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{
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warning (_("linux_ptrace_test_ret_to_nx: "
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"PTRACE_KILL status %d is not WIFSIGNALED!"),
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status);
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return;
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}
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/* + 1 is there as x86* stops after the 'int3' instruction. */
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if (WSTOPSIG (status) == SIGTRAP && pc == return_address + 1)
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{
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/* PASS */
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return;
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}
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/* We may get SIGSEGV due to missing PROT_EXEC of the RETURN_ADDRESS page. */
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if (WSTOPSIG (status) == SIGSEGV && pc == return_address)
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{
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/* PASS */
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return;
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}
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if ((void (*) (void)) pc != &linux_ptrace_test_ret_to_nx_instr)
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warning (_("linux_ptrace_test_ret_to_nx: PC %p is neither near return "
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"address %p nor is the return instruction %p!"),
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pc, return_address, &linux_ptrace_test_ret_to_nx_instr);
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else
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warning (_("Cannot call inferior functions on this system - "
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"Linux kernel with broken i386 NX (non-executable pages) "
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"support detected!"));
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#endif /* defined __i386__ || defined __x86_64__ */
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}
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/* Helper function to fork a process and make the child process call
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the function FUNCTION, passing CHILD_STACK as parameter.
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For MMU-less targets, clone is used instead of fork, and
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CHILD_STACK is used as stack space for the cloned child. If NULL,
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stack space is allocated via malloc (and subsequently passed to
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FUNCTION). For MMU targets, CHILD_STACK is ignored. */
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static int
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linux_fork_to_function (gdb_byte *child_stack, void (*function) (gdb_byte *))
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{
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int child_pid;
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/* Sanity check the function pointer. */
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gdb_assert (function != NULL);
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#if defined(__UCLIBC__) && defined(HAS_NOMMU)
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#define STACK_SIZE 4096
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if (child_stack == NULL)
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child_stack = xmalloc (STACK_SIZE * 4);
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/* Use CLONE_VM instead of fork, to support uClinux (no MMU). */
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#ifdef __ia64__
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child_pid = __clone2 (function, child_stack, STACK_SIZE,
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CLONE_VM | SIGCHLD, child_stack + STACK_SIZE * 2);
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#else /* !__ia64__ */
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child_pid = clone (function, child_stack + STACK_SIZE,
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CLONE_VM | SIGCHLD, child_stack + STACK_SIZE * 2);
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#endif /* !__ia64__ */
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#else /* !defined(__UCLIBC) && defined(HAS_NOMMU) */
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child_pid = fork ();
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if (child_pid == 0)
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function (NULL);
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#endif /* defined(__UCLIBC) && defined(HAS_NOMMU) */
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if (child_pid == -1)
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perror_with_name (("fork"));
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return child_pid;
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}
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/* A helper function for linux_check_ptrace_features, called after
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the child forks a grandchild. */
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static void
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linux_grandchild_function (gdb_byte *child_stack)
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{
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/* Free any allocated stack. */
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xfree (child_stack);
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/* This code is only reacheable by the grandchild (child's child)
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process. */
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_exit (0);
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}
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/* A helper function for linux_check_ptrace_features, called after
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the parent process forks a child. The child allows itself to
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be traced by its parent. */
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static void
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linux_child_function (gdb_byte *child_stack)
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{
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ptrace (PTRACE_TRACEME, 0, (PTRACE_TYPE_ARG3) 0, (PTRACE_TYPE_ARG4) 0);
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kill (getpid (), SIGSTOP);
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/* Fork a grandchild. */
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linux_fork_to_function (child_stack, linux_grandchild_function);
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/* This code is only reacheable by the child (grandchild's parent)
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process. */
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_exit (0);
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}
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static void linux_test_for_tracesysgood (int child_pid);
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static void linux_test_for_tracefork (int child_pid);
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/* Determine ptrace features available on this target. */
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static void
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linux_check_ptrace_features (void)
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{
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int child_pid, ret, status;
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/* Initialize the options. */
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current_ptrace_options = 0;
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/* Fork a child so we can do some testing. The child will call
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linux_child_function and will get traced. The child will
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eventually fork a grandchild so we can test fork event
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reporting. */
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child_pid = linux_fork_to_function (NULL, linux_child_function);
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ret = my_waitpid (child_pid, &status, 0);
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if (ret == -1)
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perror_with_name (("waitpid"));
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else if (ret != child_pid)
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error (_("linux_check_ptrace_features: waitpid: unexpected result %d."),
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ret);
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if (! WIFSTOPPED (status))
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error (_("linux_check_ptrace_features: waitpid: unexpected status %d."),
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status);
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linux_test_for_tracesysgood (child_pid);
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linux_test_for_tracefork (child_pid);
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/* Clean things up and kill any pending children. */
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do
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{
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ret = ptrace (PTRACE_KILL, child_pid, (PTRACE_TYPE_ARG3) 0,
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(PTRACE_TYPE_ARG4) 0);
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if (ret != 0)
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warning (_("linux_check_ptrace_features: failed to kill child"));
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my_waitpid (child_pid, &status, 0);
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}
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while (WIFSTOPPED (status));
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}
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/* Determine if PTRACE_O_TRACESYSGOOD can be used to catch
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syscalls. */
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static void
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linux_test_for_tracesysgood (int child_pid)
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{
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#ifdef GDBSERVER
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/* gdbserver does not support PTRACE_O_TRACESYSGOOD. */
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#else
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int ret;
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ret = ptrace (PTRACE_SETOPTIONS, child_pid, (PTRACE_TYPE_ARG3) 0,
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(PTRACE_TYPE_ARG4) PTRACE_O_TRACESYSGOOD);
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if (ret == 0)
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current_ptrace_options |= PTRACE_O_TRACESYSGOOD;
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#endif
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}
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/* Determine if PTRACE_O_TRACEFORK can be used to follow fork
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events. */
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static void
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linux_test_for_tracefork (int child_pid)
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{
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int ret, status;
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long second_pid;
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/* First, set the PTRACE_O_TRACEFORK option. If this fails, we
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know for sure that it is not supported. */
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ret = ptrace (PTRACE_SETOPTIONS, child_pid, (PTRACE_TYPE_ARG3) 0,
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(PTRACE_TYPE_ARG4) PTRACE_O_TRACEFORK);
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if (ret != 0)
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return;
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#ifdef GDBSERVER
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/* gdbserver does not support PTRACE_O_TRACEVFORKDONE yet. */
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#else
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/* Check if the target supports PTRACE_O_TRACEVFORKDONE. */
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ret = ptrace (PTRACE_SETOPTIONS, child_pid, (PTRACE_TYPE_ARG3) 0,
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(PTRACE_TYPE_ARG4) (PTRACE_O_TRACEFORK
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| PTRACE_O_TRACEVFORKDONE));
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if (ret == 0)
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current_ptrace_options |= PTRACE_O_TRACEVFORKDONE;
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#endif
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/* Setting PTRACE_O_TRACEFORK did not cause an error, however we
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don't know for sure that the feature is available; old
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versions of PTRACE_SETOPTIONS ignored unknown options.
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Therefore, we attach to the child process, use PTRACE_SETOPTIONS
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to enable fork tracing, and let it fork. If the process exits,
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we assume that we can't use PTRACE_O_TRACEFORK; if we get the
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fork notification, and we can extract the new child's PID, then
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we assume that we can.
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We do not explicitly check for vfork tracing here. It is
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assumed that vfork tracing is available whenever fork tracing
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is available. */
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ret = ptrace (PTRACE_CONT, child_pid, (PTRACE_TYPE_ARG3) 0,
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(PTRACE_TYPE_ARG4) 0);
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if (ret != 0)
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warning (_("linux_test_for_tracefork: failed to resume child"));
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ret = my_waitpid (child_pid, &status, 0);
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/* Check if we received a fork event notification. */
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if (ret == child_pid && WIFSTOPPED (status)
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&& status >> 16 == PTRACE_EVENT_FORK)
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{
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/* We did receive a fork event notification. Make sure its PID
|
|
is reported. */
|
|
second_pid = 0;
|
|
ret = ptrace (PTRACE_GETEVENTMSG, child_pid, (PTRACE_TYPE_ARG3) 0,
|
|
(PTRACE_TYPE_ARG4) &second_pid);
|
|
if (ret == 0 && second_pid != 0)
|
|
{
|
|
int second_status;
|
|
|
|
/* We got the PID from the grandchild, which means fork
|
|
tracing is supported. */
|
|
#ifdef GDBSERVER
|
|
/* Do not enable all the options for now since gdbserver does not
|
|
properly support them. This restriction will be lifted when
|
|
gdbserver is augmented to support them. */
|
|
current_ptrace_options |= PTRACE_O_TRACECLONE;
|
|
#else
|
|
current_ptrace_options |= PTRACE_O_TRACEFORK | PTRACE_O_TRACEVFORK
|
|
| PTRACE_O_TRACECLONE | PTRACE_O_TRACEEXEC;
|
|
|
|
/* Do not enable PTRACE_O_TRACEEXIT until GDB is more prepared to
|
|
support read-only process state. */
|
|
#endif
|
|
|
|
/* Do some cleanup and kill the grandchild. */
|
|
my_waitpid (second_pid, &second_status, 0);
|
|
ret = ptrace (PTRACE_KILL, second_pid, (PTRACE_TYPE_ARG3) 0,
|
|
(PTRACE_TYPE_ARG4) 0);
|
|
if (ret != 0)
|
|
warning (_("linux_test_for_tracefork: "
|
|
"failed to kill second child"));
|
|
my_waitpid (second_pid, &status, 0);
|
|
}
|
|
}
|
|
else
|
|
warning (_("linux_test_for_tracefork: unexpected result from waitpid "
|
|
"(%d, status 0x%x)"), ret, status);
|
|
}
|
|
|
|
/* Enable reporting of all currently supported ptrace events. */
|
|
|
|
void
|
|
linux_enable_event_reporting (pid_t pid)
|
|
{
|
|
/* Check if we have initialized the ptrace features for this
|
|
target. If not, do it now. */
|
|
if (current_ptrace_options == -1)
|
|
linux_check_ptrace_features ();
|
|
|
|
/* Set the options. */
|
|
ptrace (PTRACE_SETOPTIONS, pid, (PTRACE_TYPE_ARG3) 0,
|
|
(PTRACE_TYPE_ARG4) (uintptr_t) current_ptrace_options);
|
|
}
|
|
|
|
/* Returns non-zero if PTRACE_OPTIONS is contained within
|
|
CURRENT_PTRACE_OPTIONS, therefore supported. Returns 0
|
|
otherwise. */
|
|
|
|
static int
|
|
ptrace_supports_feature (int ptrace_options)
|
|
{
|
|
gdb_assert (current_ptrace_options >= 0);
|
|
|
|
return ((current_ptrace_options & ptrace_options) == ptrace_options);
|
|
}
|
|
|
|
/* Returns non-zero if PTRACE_EVENT_FORK is supported by ptrace,
|
|
0 otherwise. Note that if PTRACE_EVENT_FORK is supported so is
|
|
PTRACE_EVENT_CLONE, PTRACE_EVENT_EXEC and PTRACE_EVENT_VFORK,
|
|
since they were all added to the kernel at the same time. */
|
|
|
|
int
|
|
linux_supports_tracefork (void)
|
|
{
|
|
return ptrace_supports_feature (PTRACE_O_TRACEFORK);
|
|
}
|
|
|
|
/* Returns non-zero if PTRACE_EVENT_CLONE is supported by ptrace,
|
|
0 otherwise. Note that if PTRACE_EVENT_CLONE is supported so is
|
|
PTRACE_EVENT_FORK, PTRACE_EVENT_EXEC and PTRACE_EVENT_VFORK,
|
|
since they were all added to the kernel at the same time. */
|
|
|
|
int
|
|
linux_supports_traceclone (void)
|
|
{
|
|
return ptrace_supports_feature (PTRACE_O_TRACECLONE);
|
|
}
|
|
|
|
/* Returns non-zero if PTRACE_O_TRACEVFORKDONE is supported by
|
|
ptrace, 0 otherwise. */
|
|
|
|
int
|
|
linux_supports_tracevforkdone (void)
|
|
{
|
|
return ptrace_supports_feature (PTRACE_O_TRACEVFORKDONE);
|
|
}
|
|
|
|
/* Returns non-zero if PTRACE_O_TRACESYSGOOD is supported by ptrace,
|
|
0 otherwise. */
|
|
|
|
int
|
|
linux_supports_tracesysgood (void)
|
|
{
|
|
return ptrace_supports_feature (PTRACE_O_TRACESYSGOOD);
|
|
}
|
|
|
|
/* Display possible problems on this system. Display them only once per GDB
|
|
execution. */
|
|
|
|
void
|
|
linux_ptrace_init_warnings (void)
|
|
{
|
|
static int warned = 0;
|
|
|
|
if (warned)
|
|
return;
|
|
warned = 1;
|
|
|
|
linux_ptrace_test_ret_to_nx ();
|
|
}
|