diff options
| -rw-r--r-- | gdbstub/user.c | 212 |
1 files changed, 210 insertions, 2 deletions
diff --git a/gdbstub/user.c b/gdbstub/user.c index 1a7b582a40..7f9f19a124 100644 --- a/gdbstub/user.c +++ b/gdbstub/user.c @@ -25,6 +25,61 @@ #define GDB_NR_SYSCALLS 1024 typedef unsigned long GDBSyscallsMask[BITS_TO_LONGS(GDB_NR_SYSCALLS)]; +/* + * Forked child talks to its parent in order to let GDB enforce the + * follow-fork-mode. This happens inside a start_exclusive() section, so that + * the other threads, which may be forking too, do not interfere. The + * implementation relies on GDB not sending $vCont until it has detached + * either from the parent (follow-fork-mode child) or from the child + * (follow-fork-mode parent). + * + * The parent and the child share the GDB socket; at any given time only one + * of them is allowed to use it, as is reflected in the respective fork_state. + * This is negotiated via the fork_sockets pair as a reaction to $Hg. + * + * Below is a short summary of the possible state transitions: + * + * ENABLED : Terminal state. + * DISABLED : Terminal state. + * ACTIVE : Parent initial state. + * INACTIVE : Child initial state. + * ACTIVE -> DEACTIVATING: On $Hg. + * ACTIVE -> ENABLING : On $D. + * ACTIVE -> DISABLING : On $D. + * ACTIVE -> DISABLED : On communication error. + * DEACTIVATING -> INACTIVE : On gdb_read_byte() return. + * DEACTIVATING -> DISABLED : On communication error. + * INACTIVE -> ACTIVE : On $Hg in the peer. + * INACTIVE -> ENABLE : On $D in the peer. + * INACTIVE -> DISABLE : On $D in the peer. + * INACTIVE -> DISABLED : On communication error. + * ENABLING -> ENABLED : On gdb_read_byte() return. + * ENABLING -> DISABLED : On communication error. + * DISABLING -> DISABLED : On gdb_read_byte() return. + */ +enum GDBForkState { + /* Fully owning the GDB socket. */ + GDB_FORK_ENABLED, + /* Working with the GDB socket; the peer is inactive. */ + GDB_FORK_ACTIVE, + /* Handing off the GDB socket to the peer. */ + GDB_FORK_DEACTIVATING, + /* The peer is working with the GDB socket. */ + GDB_FORK_INACTIVE, + /* Asking the peer to close its GDB socket fd. */ + GDB_FORK_ENABLING, + /* Asking the peer to take over, closing our GDB socket fd. */ + GDB_FORK_DISABLING, + /* The peer has taken over, our GDB socket fd is closed. */ + GDB_FORK_DISABLED, +}; + +enum GDBForkMessage { + GDB_FORK_ACTIVATE = 'a', + GDB_FORK_ENABLE = 'e', + GDB_FORK_DISABLE = 'd', +}; + /* User-mode specific state */ typedef struct { int fd; @@ -36,6 +91,10 @@ typedef struct { */ bool catch_all_syscalls; GDBSyscallsMask catch_syscalls_mask; + bool fork_events; + enum GDBForkState fork_state; + int fork_sockets[2]; + pid_t fork_peer_pid, fork_peer_tid; } GDBUserState; static GDBUserState gdbserver_user_state; @@ -358,6 +417,18 @@ int gdbserver_start(const char *port_or_path) void gdbserver_fork_start(void) { + if (!gdbserver_state.init || gdbserver_user_state.fd < 0) { + return; + } + if (!gdbserver_user_state.fork_events || + qemu_socketpair(AF_UNIX, SOCK_STREAM, 0, + gdbserver_user_state.fork_sockets) < 0) { + gdbserver_user_state.fork_state = GDB_FORK_DISABLED; + return; + } + gdbserver_user_state.fork_state = GDB_FORK_INACTIVE; + gdbserver_user_state.fork_peer_pid = getpid(); + gdbserver_user_state.fork_peer_tid = qemu_get_thread_id(); } static void disable_gdbstub(CPUState *thread_cpu) @@ -376,23 +447,160 @@ static void disable_gdbstub(CPUState *thread_cpu) void gdbserver_fork_end(CPUState *cpu, pid_t pid) { - if (pid != 0 || !gdbserver_state.init || gdbserver_user_state.fd < 0) { + char b; + int fd; + + if (!gdbserver_state.init || gdbserver_user_state.fd < 0) { return; } - disable_gdbstub(cpu); + + if (pid == -1) { + if (gdbserver_user_state.fork_state != GDB_FORK_DISABLED) { + g_assert(gdbserver_user_state.fork_state == GDB_FORK_INACTIVE); + close(gdbserver_user_state.fork_sockets[0]); + close(gdbserver_user_state.fork_sockets[1]); + } + return; + } + + if (gdbserver_user_state.fork_state == GDB_FORK_DISABLED) { + if (pid == 0) { + disable_gdbstub(cpu); + } + return; + } + + if (pid == 0) { + close(gdbserver_user_state.fork_sockets[0]); + fd = gdbserver_user_state.fork_sockets[1]; + g_assert(gdbserver_state.process_num == 1); + g_assert(gdbserver_state.processes[0].pid == + gdbserver_user_state.fork_peer_pid); + g_assert(gdbserver_state.processes[0].attached); + gdbserver_state.processes[0].pid = getpid(); + } else { + close(gdbserver_user_state.fork_sockets[1]); + fd = gdbserver_user_state.fork_sockets[0]; + gdbserver_user_state.fork_state = GDB_FORK_ACTIVE; + gdbserver_user_state.fork_peer_pid = pid; + gdbserver_user_state.fork_peer_tid = pid; + + if (!gdbserver_state.allow_stop_reply) { + goto fail; + } + g_string_printf(gdbserver_state.str_buf, + "T%02xfork:p%02x.%02x;thread:p%02x.%02x;", + gdb_target_signal_to_gdb(gdb_target_sigtrap()), + pid, pid, (int)getpid(), qemu_get_thread_id()); + gdb_put_strbuf(); + } + + gdbserver_state.state = RS_IDLE; + gdbserver_state.allow_stop_reply = false; + gdbserver_user_state.running_state = 0; + for (;;) { + switch (gdbserver_user_state.fork_state) { + case GDB_FORK_ENABLED: + if (gdbserver_user_state.running_state) { + return; + } + QEMU_FALLTHROUGH; + case GDB_FORK_ACTIVE: + if (read(gdbserver_user_state.fd, &b, 1) != 1) { + goto fail; + } + gdb_read_byte(b); + break; + case GDB_FORK_DEACTIVATING: + b = GDB_FORK_ACTIVATE; + if (write(fd, &b, 1) != 1) { + goto fail; + } + gdbserver_user_state.fork_state = GDB_FORK_INACTIVE; + break; + case GDB_FORK_INACTIVE: + if (read(fd, &b, 1) != 1) { + goto fail; + } + switch (b) { + case GDB_FORK_ACTIVATE: + gdbserver_user_state.fork_state = GDB_FORK_ACTIVE; + break; + case GDB_FORK_ENABLE: + close(fd); + gdbserver_user_state.fork_state = GDB_FORK_ENABLED; + break; + case GDB_FORK_DISABLE: + gdbserver_user_state.fork_state = GDB_FORK_DISABLED; + break; + default: + g_assert_not_reached(); + } + break; + case GDB_FORK_ENABLING: + b = GDB_FORK_DISABLE; + if (write(fd, &b, 1) != 1) { + goto fail; + } + close(fd); + gdbserver_user_state.fork_state = GDB_FORK_ENABLED; + break; + case GDB_FORK_DISABLING: + b = GDB_FORK_ENABLE; + if (write(fd, &b, 1) != 1) { + goto fail; + } + gdbserver_user_state.fork_state = GDB_FORK_DISABLED; + break; + case GDB_FORK_DISABLED: + close(fd); + disable_gdbstub(cpu); + return; + default: + g_assert_not_reached(); + } + } + +fail: + close(fd); + if (pid == 0) { + disable_gdbstub(cpu); + } } void gdb_handle_query_supported_user(const char *gdb_supported) { + if (strstr(gdb_supported, "fork-events+")) { + gdbserver_user_state.fork_events = true; + } + g_string_append(gdbserver_state.str_buf, ";fork-events+"); } bool gdb_handle_set_thread_user(uint32_t pid, uint32_t tid) { + if (gdbserver_user_state.fork_state == GDB_FORK_ACTIVE && + pid == gdbserver_user_state.fork_peer_pid && + tid == gdbserver_user_state.fork_peer_tid) { + gdbserver_user_state.fork_state = GDB_FORK_DEACTIVATING; + gdb_put_packet("OK"); + return true; + } return false; } bool gdb_handle_detach_user(uint32_t pid) { + bool enable; + + if (gdbserver_user_state.fork_state == GDB_FORK_ACTIVE) { + enable = pid == gdbserver_user_state.fork_peer_pid; + if (enable || pid == getpid()) { + gdbserver_user_state.fork_state = enable ? GDB_FORK_ENABLING : + GDB_FORK_DISABLING; + gdb_put_packet("OK"); + return true; + } + } return false; } |