buildman: Add a flag for reproducible builds

This is quite a useful thing to use when building since it avoids small
size changes between commits. Add a -r flag for it.

Also undefine CONFIG_LOCALVERSION_AUTO since this appends the git hash
to the version string, causing every build to be slightly different.

Signed-off-by: Simon Glass <sjg@chromium.org>

7 files changed, 56 insertions, 12 deletions

diff --git a/doc/build/reproducible.rst b/doc/build/reproducible.rst
index 5423080633..8b030f469d 100644
--- a/doc/build/reproducible.rst
+++ b/doc/build/reproducible.rst
@@ -23,3 +23,5 @@ This date is shown when we launch U-Boot:
 
     ./u-boot -T
     U-Boot 2023.01 (Jan 01 2023 - 00:00:00 +0000)
+
+The same effect can be obtained with buildman using the `-r` flag.
diff --git a/tools/buildman/builder.py b/tools/buildman/builder.py
index 107086cc0e..7b9be887e5 100644
--- a/tools/buildman/builder.py
+++ b/tools/buildman/builder.py
@@ -195,6 +195,7 @@ class Builder:
             don't write to a separate output directory.
         thread_exceptions: List of exceptions raised by thread jobs
         no_lto (bool): True to set the NO_LTO flag when building
+        reproducible_builds (bool): True to set SOURCE_DATE_EPOCH=0 for builds
 
     Private members:
         _base_board_dict: Last-summarised Dict of boards
@@ -254,7 +255,7 @@ class Builder:
                  config_only=False, squash_config_y=False,
                  warnings_as_errors=False, work_in_output=False,
                  test_thread_exceptions=False, adjust_cfg=None,
-                 allow_missing=False, no_lto=False):
+                 allow_missing=False, no_lto=False, reproducible_builds=False):
         """Create a new Builder object
 
         Args:
@@ -334,6 +335,7 @@ class Builder:
         self.allow_missing = allow_missing
         self._ide = False
         self.no_lto = no_lto
+        self.reproducible_builds = reproducible_builds
 
         if not self.squash_config_y:
             self.config_filenames += EXTRA_CONFIG_FILENAMES
diff --git a/tools/buildman/builderthread.py b/tools/buildman/builderthread.py
index dae3d4ab9f..8b88c68e5d 100644
--- a/tools/buildman/builderthread.py
+++ b/tools/buildman/builderthread.py
@@ -257,6 +257,8 @@ class BuilderThread(threading.Thread):
                     args.append('BINMAN_ALLOW_MISSING=1')
                 if self.builder.no_lto:
                     args.append('NO_LTO=1')
+                if self.builder.reproducible_builds:
+                    args.append('SOURCE_DATE_EPOCH=0')
                 config_args = ['%s_defconfig' % brd.target]
                 config_out = ''
                 args.extend(self.builder.toolchains.GetMakeArguments(brd))
diff --git a/tools/buildman/buildman.rst b/tools/buildman/buildman.rst
index 800b83a89d..c8b0db3d8b 100644
--- a/tools/buildman/buildman.rst
+++ b/tools/buildman/buildman.rst
@@ -1023,14 +1023,15 @@ U-Boot's build system embeds information such as a build timestamp into the
 final binary. This information varies each time U-Boot is built. This causes
 various files to be rebuilt even if no source changes are made, which in turn
 requires that the final U-Boot binary be re-linked. This unnecessary work can
-be avoided by turning off the timestamp feature. This can be achieved by
-setting the SOURCE_DATE_EPOCH environment variable to 0.
+be avoided by turning off the timestamp feature. This can be achieved using
+the `-r` flag, which enables reproducible builds by setting
+`SOURCE_DATE_EPOCH=0` when building.
 
 Combining all of these options together yields the command-line shown below.
 This will provide the quickest possible feedback regarding the current content
 of the source tree, thus allowing rapid tested evolution of the code::
 
-    SOURCE_DATE_EPOCH=0 ./tools/buildman/buildman -P tegra
+    ./tools/buildman/buildman -Pr tegra
 
 
 Checking configuration
diff --git a/tools/buildman/cmdline.py b/tools/buildman/cmdline.py
index 409013671b..da7f1a99f6 100644
--- a/tools/buildman/cmdline.py
+++ b/tools/buildman/cmdline.py
@@ -97,6 +97,8 @@ def ParseArgs():
           default=False, help="Use full toolchain path in CROSS_COMPILE")
     parser.add_option('-P', '--per-board-out-dir', action='store_true',
           default=False, help="Use an O= (output) directory per board rather than per thread")
+    parser.add_option('-r', '--reproducible-builds', action='store_true',
+          help='Set SOURCE_DATE_EPOCH=0 to suuport a reproducible build')
     parser.add_option('-R', '--regen-board-list', action='store_true',
           help='Force regeneration of the list of boards, like the old boards.cfg file')
     parser.add_option('-s', '--summary', action='store_true',
diff --git a/tools/buildman/control.py b/tools/buildman/control.py
index 13a462ae59..c3c5388199 100644
--- a/tools/buildman/control.py
+++ b/tools/buildman/control.py
@@ -338,6 +338,14 @@ def DoBuildman(options, args, toolchains=None, make_func=None, brds=None,
             shutil.rmtree(output_dir)
     adjust_cfg = cfgutil.convert_list_to_dict(options.adjust_cfg)
 
+    # Drop LOCALVERSION_AUTO since it changes the version string on every commit
+    if options.reproducible_builds:
+        # If these are mentioned, leave the local version alone
+        if 'LOCALVERSION' in adjust_cfg or 'LOCALVERSION_AUTO' in adjust_cfg:
+            print('Not dropping LOCALVERSION_AUTO for reproducible build')
+        else:
+            adjust_cfg['LOCALVERSION_AUTO'] = '~'
+
     builder = Builder(toolchains, output_dir, options.git_dir,
             options.threads, options.jobs, gnu_make=gnu_make, checkout=True,
             show_unknown=options.show_unknown, step=options.step,
@@ -351,7 +359,8 @@ def DoBuildman(options, args, toolchains=None, make_func=None, brds=None,
             work_in_output=options.work_in_output,
             test_thread_exceptions=test_thread_exceptions,
             adjust_cfg=adjust_cfg,
-            allow_missing=allow_missing, no_lto=options.no_lto)
+            allow_missing=allow_missing, no_lto=options.no_lto,
+            reproducible_builds=options.reproducible_builds)
     builder.force_config_on_failure = not options.quick
     if make_func:
         builder.do_make = make_func
diff --git a/tools/buildman/func_test.py b/tools/buildman/func_test.py
index 6d1557293f..cf91c33913 100644
--- a/tools/buildman/func_test.py
+++ b/tools/buildman/func_test.py
@@ -415,17 +415,19 @@ class TestFunctional(unittest.TestCase):
             kwargs: Arguments to pass to command.run_pipe()
         """
         self._make_calls += 1
+        out_dir = ''
+        for arg in args:
+            if arg.startswith('O='):
+                out_dir = arg[2:]
         if stage == 'mrproper':
             return command.CommandResult(return_code=0)
         elif stage == 'config':
+            fname = os.path.join(cwd or '', out_dir, '.config')
+            tools.write_file(fname, b'CONFIG_SOMETHING=1')
             return command.CommandResult(return_code=0,
                     combined='Test configuration complete')
         elif stage == 'build':
             stderr = ''
-            out_dir = ''
-            for arg in args:
-                if arg.startswith('O='):
-                    out_dir = arg[2:]
             fname = os.path.join(cwd or '', out_dir, 'u-boot')
             tools.write_file(fname, b'U-Boot')
 
@@ -739,17 +741,41 @@ Some images are invalid'''
         cmd_fname = os.path.join(board0_dir, 'out-cmd')
         self.assertTrue(os.path.exists(cmd_fname))
         data = tools.read_file(cmd_fname)
-        return data.splitlines()
+
+        config_fname = os.path.join(board0_dir, '.config')
+        self.assertTrue(os.path.exists(config_fname))
+        cfg_data = tools.read_file(config_fname)
+
+        return data.splitlines(), cfg_data
 
     def testCmdFile(self):
         """Test that the -cmd-out file is produced"""
-        lines = self.check_command()
+        lines = self.check_command()[0]
         self.assertEqual(2, len(lines))
         self.assertRegex(lines[0], b'make O=/.*board0_defconfig')
         self.assertRegex(lines[0], b'make O=/.*-s.*')
 
     def testNoLto(self):
         """Test that the --no-lto flag works"""
-        lines = self.check_command('-L')
+        lines = self.check_command('-L')[0]
         self.assertIn(b'NO_LTO=1', lines[0])
 
+    def testReproducible(self):
+        """Test that the -r flag works"""
+        lines, cfg_data = self.check_command('-r')
+        self.assertIn(b'SOURCE_DATE_EPOCH=0', lines[0])
+
+        # We should see CONFIG_LOCALVERSION_AUTO unset
+        self.assertEqual(b'''CONFIG_SOMETHING=1
+# CONFIG_LOCALVERSION_AUTO is not set
+''', cfg_data)
+
+        with test_util.capture_sys_output() as (stdout, stderr):
+            lines, cfg_data = self.check_command('-r', '-a', 'LOCALVERSION')
+        self.assertIn(b'SOURCE_DATE_EPOCH=0', lines[0])
+
+        # We should see CONFIG_LOCALVERSION_AUTO unset
+        self.assertEqual(b'''CONFIG_SOMETHING=1
+CONFIG_LOCALVERSION=y
+''', cfg_data)
+        self.assertIn('Not dropping LOCALVERSION_AUTO', stdout.getvalue())