sysprofd: add support for unwinding without frame pointers

This provides a new sysprof-live-unwinder subprocess that runs as root to
allow accessing all processes on the system via /proc/$pid/. It is spawned
by sysprofd with various perf event FDs and a FD to write captures to.

Ideally the capture_fd is something that will naturally error if the client
application crashes (such as a socketpair() having the peer close). This
is not enforced but encouraged. Additionally, an event_fd is used to allow
the client application to signal the live-unwinder to exit.

Unwinding is performed by looking at the modules loaded into the target
pid and using libdwfl to access DWARF/CFI/etc state machinery. Stack data
does not touch the disk as it exists in a mmap buffer from perf and is
then translated into a callchain and sent to the Sysprof client.

Unwinding occurs as normal post-mortem though is improved through the use
of debuginfod to locate the appropriate symbols.

src/sysprof-live-unwinder/sysprof-live-process.h

@@ -0,0 +1,50 @@
+/*
+ * sysprof-live-pid.h
+ *
+ * Copyright 2024 Christian Hergert <chergert@redhat.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#pragma once
+
+#include <glib.h>
+
+G_BEGIN_DECLS
+
+typedef struct _SysprofLiveProcess SysprofLiveProcess;
+
+SysprofLiveProcess *sysprof_live_process_new       (GPid                pid);
+SysprofLiveProcess *sysprof_live_process_ref       (SysprofLiveProcess *self);
+void                sysprof_live_process_unref     (SysprofLiveProcess *self);
+gboolean            sysprof_live_process_is_active (SysprofLiveProcess *self);
+void                sysprof_live_process_add_map   (SysprofLiveProcess *self,
+                                                    guint64             begin,
+                                                    guint64             end,
+                                                    guint64             offset,
+                                                    guint64             inode,
+                                                    const char         *filename);
+guint               sysprof_live_process_unwind    (SysprofLiveProcess *self,
+                                                    GPid                tid,
+                                                    guint64             abi,
+                                                    const guint8       *stack,
+                                                    gsize               stack_len,
+                                                    const guint64      *registers,
+                                                    guint               n_registers,
+                                                    guint64            *addresses,
+                                                    guint               n_addresses);
+
+G_END_DECLS