qemu: document GDB user mode, fix some stuff

README.adoc

@@ -7699,6 +7699,26 @@ It is already usable with:
 
 TODO: factor <<qemu-user-mode>> with this:
 
+===== QEMU user mode GDB
+
+It's nice when the obvious works, right?
+
+....
+./run --debug-guest --user ./x86_64.out
+....
+
+and on another shell:
+
+....
+./run-gdb --user ./x86_64.out main
+....
+
+or to stop at the very first instruction of a freestanding program:
+
+....
+./run-gdb --no-continue --user ./x86_64.out
+....
+
 ==== gem5 syscall emulation mode
 
 Analogous to <<qemu-user-mode>>, but less usable:
@@ -7752,7 +7772,7 @@ Then I was told that it is has never been tested outside of x86_64:
 ===== gem5 syscall emulation mode CLI options
 
 ....
-./run --gem5 --user ./aarch64.out -- --options 'op1 "op 2" op3'
+./run --gem5 --user ./x86_64.out -- --options 'op1 "op 2" op3'
 ....
 
 ==== User mode vs full system benchmark

common.py

@@ -792,6 +792,7 @@ def setup(parser):
     # Kernel modules.
     this_module.kernel_modules_build_base_dir = os.path.join(this_module.out_dir, 'kernel_modules')
     this_module.kernel_modules_build_dir = os.path.join(this_module.kernel_modules_build_base_dir, args.arch)
+    this_module.kernel_modules_build_subdir = os.path.join(this_module.kernel_modules_build_dir, kernel_modules_subdir)
     this_module.kernel_modules_build_host_dir = os.path.join(this_module.kernel_modules_build_base_dir, 'host')
     this_module.userland_build_dir = os.path.join(this_module.out_dir, 'userland', args.arch)
     this_module.out_rootfs_overlay_dir = os.path.join(this_module.out_dir, 'rootfs_overlay', args.arch)

run

@@ -36,6 +36,7 @@ defaults = {
     'tmux_args': '',
     'trace': None,
     'user': None,
+    'user_before': '',
     'vnc': False,
 }
 
@@ -91,7 +92,7 @@ def main(args, extra_args=None):
         do_trace = False
         # A dummy value that is already turned on by default and does not produce large output,
         # just to prevent QEMU from emitting a warning that '' is not valid.
-        trace_type = 'pr_manager_run'
+        trace_type = 'load_file'
     else:
         do_trace = True
         trace_type = args.trace
@@ -205,6 +206,7 @@ def main(args, extra_args=None):
                     os.path.join(common.qemu_build_dir, '{}-linux-user'.format(args.arch), 'qemu-{}'.format(args.arch)),
                 ] +
                 qemu_user_and_system_options +
+                shlex.split(args.user_before) +
                 debug_args +
                 [
                     args.user
@@ -503,6 +505,12 @@ to use this option:
         help='''\
 Run the given userland executable in user mode instead of full system mode.
 In gem5, user mode is called Syscall Emulation (SE) mode and uses se.py.
+'''
+    )
+    parser.add_argument(
+        '--user-before', default=defaults['user_before'],
+        help='''\
+Arguments to pass to the QEMU user mode CLI before the program to execute.
 '''
     )
     parser.add_argument(

run-gdb

@@ -11,11 +11,12 @@ import common
 defaults = {
     'after': '',
     'before': '',
-    'sim': False,
-    'no_continue': False,
-    'kgdb': False,
-    'no_lxsymbols': False,
     'break_at': None,
+    'kgdb': False,
+    'no_continue': False,
+    'no_lxsymbols': False,
+    'sim': False,
+    'user': None,
 }
 
 def main(args, extra_args=None):
@@ -34,26 +35,27 @@ def main(args, extra_args=None):
     args = common.resolve_args(defaults, args, extra_args)
     after = shlex.split(args.after)
     before = shlex.split(args.before)
-    if args.no_lxsymbols or args.baremetal is not None:
-        lx_symbols = []
-    else:
-        lx_symbols = ['-ex', 'lx-symbols {}'.format(common.kernel_modules_build_subdir)]
     if args.break_at is not None:
         break_at = ['-ex', 'break {}'.format(args.break_at)]
     else:
         break_at = []
-    if args.baremetal is None:
-        image = common.vmlinux
-        allowed_toolchains = ['buildroot', 'crosstool-ng', 'host']
+    linux_full_system = (args.baremetal is None and args.user is None)
+    if args.user:
+        image = args.user
+    elif args.baremetal:
+        image = args.baremetal
     else:
-        image = common.image
+        image = common.vmlinux
+    if args.baremetal:
         allowed_toolchains = ['crosstool-ng', 'buildroot', 'host']
+    else:
+        allowed_toolchains = ['buildroot', 'crosstool-ng', 'host']
     cmd = (
         [common.get_toolchain_tool('gdb', allowed_toolchains=allowed_toolchains)] +
         before +
         ['-q']
     )
-    if args.baremetal is None:
+    if linux_full_system:
         cmd.extend(['-ex', 'add-auto-load-safe-path {}'.format(common.linux_build_dir)])
     if args.sim:
         target = 'sim'
@@ -85,7 +87,9 @@ def main(args, extra_args=None):
         #
         # The lx-symbols commands gets loaded through the file vmlinux-gdb.py
         # which gets put on the kernel build root when python debugging scripts are enabled.
-        cmd.extend(['-ex', 'continue'] + lx_symbols)
+        cmd.extend(['-ex', 'continue'])
+        if not args.no_lxsymbols and linux_full_system:
+            cmd.extend(['-ex', 'lx-symbols {}'.format(common.kernel_modules_build_subdir)])
     cmd.extend(after)
     return common.run_cmd(cmd, cmd_file=os.path.join(common.run_dir, 'run-gdb.sh'), cwd=common.linux_build_dir)
 
@@ -115,6 +119,9 @@ See: https://github.com/cirosantilli/linux-kernel-module-cheat#gdb-builtin-cpu-s
     parser.add_argument(
         '-X', '--no-lxsymbols', default=defaults['no_lxsymbols'], action='store_true'
     )
+    parser.add_argument(
+        '--user', default=defaults['user'],
+    )
     parser.add_argument(
         'break_at', nargs='?',
         help='Extra options to append at the end of the emulator command line'