From 5c06845e8676e5df693ca0186889f85fae667f13 Mon Sep 17 00:00:00 2001
From: Christian Hergert <chergert@redhat.com>
Date: Mon, 20 Feb 2023 21:04:21 -0800
Subject: [PATCH] tools: add helper to rewrite a PID

This is mostly useful when troubleshooting PIDs in container namespaces
that don't match the host.
---
 src/tools/meson.build   |  18 ++++--
 src/tools/rewrite-pid.c | 129 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 142 insertions(+), 5 deletions(-)
 create mode 100644 src/tools/rewrite-pid.c

diff --git a/src/tools/meson.build b/src/tools/meson.build
index 20d24f2a..c48c4e10 100644
--- a/src/tools/meson.build
+++ b/src/tools/meson.build
@@ -18,11 +18,19 @@ sysprof_cat = executable('sysprof-cat', 'sysprof-cat.c',
        install: false,
 )
 
-sysprof_dump = executable('sysprof-dump', 'sysprof-dump.c',
-  dependencies: [libsysprof_dep],
-        c_args: tools_cflags,
-       install: false,
-)
+if get_option('libsysprof')
+  sysprof_dump = executable('sysprof-dump', 'sysprof-dump.c',
+    dependencies: [libsysprof_dep],
+          c_args: tools_cflags,
+         install: false,
+  )
+
+  rewrite_pid = executable('rewrite-pid', ['rewrite-pid.c'],
+    dependencies: [libsysprof_dep],
+          c_args: tools_cflags,
+         install: false,
+  )
+endif
 
 if get_option('sysprofd') == 'bundled' or get_option('libsysprof')
   sysprof_profiler_ctl = executable('sysprof-profiler-ctl',
diff --git a/src/tools/rewrite-pid.c b/src/tools/rewrite-pid.c
new file mode 100644
index 00000000..07825ec3
--- /dev/null
+++ b/src/tools/rewrite-pid.c
@@ -0,0 +1,129 @@
+/* rewrite-pid.c
+ *
+ * Copyright 2023 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
+ */
+
+#include "config.h"
+
+#include <gio/gio.h>
+#include <sysprof-capture.h>
+
+/* Rewrite a capture file to change PID X to Y */
+
+static void
+rewrite_pid (guint8 *data,
+             gsize   len,
+             int     old_pid,
+             int     new_pid)
+{
+  SysprofCaptureFileHeader header;
+  guint8 *endptr = &data[len];
+  guint8 *frameptr = (guint8 *)&data[sizeof (SysprofCaptureFileHeader)];
+  gboolean swap;
+
+  if (len < sizeof header)
+    return;
+
+  memcpy (&header, data, sizeof header);
+
+#if G_BYTE_ORDER == G_LITTLE_ENDIAN
+  swap = !header.little_endian;
+#else
+  swap = header.little_endian;
+#endif
+
+  if (swap)
+    {
+      old_pid = GUINT16_SWAP_LE_BE (old_pid);
+      new_pid = GUINT16_SWAP_LE_BE (new_pid);
+    }
+
+  while (frameptr < endptr)
+    {
+      SysprofCaptureFrame *frame = (SysprofCaptureFrame *)frameptr;
+
+      if (frame->pid == old_pid)
+        frame->pid = new_pid;
+
+      if (swap)
+        frameptr += GUINT16_SWAP_LE_BE (frame->len);
+      else
+        frameptr += frame->len;
+    }
+}
+
+static gboolean
+parse_args (int          argc,
+            char       **argv,
+            const char **file,
+            int         *old_pid,
+            int         *new_pid)
+{
+  if (argc != 4)
+    return FALSE;
+
+  *file = argv[1];
+
+  if (!g_file_test (*file, G_FILE_TEST_IS_REGULAR))
+    return FALSE;
+
+  *old_pid = g_ascii_strtoll (argv[2], NULL, 10);
+  *new_pid = g_ascii_strtoll (argv[3], NULL, 10);
+
+  return *old_pid != 0 && *new_pid != 0;
+}
+
+int main (int argc,
+          char *argv[])
+{
+  g_autoptr(GBytes) bytes = NULL;
+  g_autoptr(GError) error = NULL;
+  g_autoptr(GFile) gfile = NULL;
+  const char *file;
+  int old;
+  int new;
+
+  if (!parse_args (argc, argv, &file, &old, &new))
+    {
+      g_printerr ("usage: rewrite-pid FILE OLD_PID NEW_PID\n");
+      return 1;
+    }
+
+  gfile = g_file_new_for_commandline_arg (file);
+
+  if (!(bytes = g_file_load_bytes (gfile, NULL, NULL, &error)))
+    {
+      g_printerr ("error: %s\n", error->message);
+      return 1;
+    }
+
+  rewrite_pid ((guint8 *)g_bytes_get_data (bytes, NULL),
+               g_bytes_get_size (bytes),
+               old, new);
+
+  if (!g_file_set_contents (file,
+                            (const char *)g_bytes_get_data (bytes, NULL),
+                            g_bytes_get_size (bytes),
+                            &error))
+    {
+      g_printerr ("error: %s\n", error->message);
+      return 1;
+    }
+
+  return 0;
+}