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Date:   Tue, 12 Jan 2021 16:54:57 +0100
From:   Jessica Yu <jeyu@kernel.org>
To:     Will McVicker <willmcvicker@google.com>
Cc:     Masahiro Yamada <masahiroy@kernel.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Christoph Hellwig <hch@infradead.org>,
        Saravana Kannan <saravanak@google.com>,
        linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org,
        kernel-team@android.com
Subject: Re: [PATCH v5] modules: introduce the MODULE_SCMVERSION config
Message-ID: <20210112155456.GB26122@linux-8ccs>
References: <20210108003035.1930475-1-willmcvicker@google.com>
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+++ Will McVicker [08/01/21 00:30 +0000]:
>Config MODULE_SCMVERSION introduces a new module attribute --
>`scmversion` -- which can be used to identify a given module's SCM
>version.  This is very useful for developers that update their kernel
>independently from their kernel modules or vice-versa since the SCM
>version provided by UTS_RELEASE (`uname -r`) will now differ from the
>module's vermagic attribute.
>
>For example, we have a CI setup that tests new kernel changes on the
>hikey960 and db845c devices without updating their kernel modules. When
>these tests fail, we need to be able to identify the exact device
>configuration the test was using. By including MODULE_SCMVERSION, we can
>identify the exact kernel and modules' SCM versions for debugging the
>failures.
>
>Additionally, by exposing the SCM version via the sysfs node
>/sys/module/MODULENAME/scmversion, one can also verify the SCM versions
>of the modules loaded from the initramfs. Currently, modinfo can only
>retrieve module attributes from the module's ko on disk and not from the
>actual module that is loaded in RAM.
>
>You can retrieve the SCM version in two ways,
>
>1) By using modinfo:
>    > modinfo -F scmversion MODULENAME
>2) By module sysfs node:
>    > cat /sys/module/MODULENAME/scmversion
>
>Signed-off-by: Will McVicker <willmcvicker@google.com>

Hi Will,

Thanks for v5, I'm fine with this patch now that we've made it a
configurable developer/debug option to supply an scmversion field for
in-tree modules (although, this currently works for out-of-tree
modules too since we based module_srcpath on KBUILD_EXTMOD in the
external module case). I basically see this option as an alternative
to CONFIG_MODULE_SRCVERSION_ALL to aid distro developers debug issues
when the kernel and in-tree modules are updated separately.

In any case, since there was pushback in our earlier discussions, I'd
like to ask if there are any remaining objections to this patch.

Masahiro, are you fine with the Makefile and modpost changes?

Thanks,

Jessica

>---
> Documentation/ABI/stable/sysfs-module | 18 ++++++++++++++++++
> include/linux/module.h                |  1 +
> init/Kconfig                          | 14 ++++++++++++++
> kernel/module.c                       |  2 ++
> scripts/Makefile.modpost              | 22 ++++++++++++++++++++++
> scripts/mod/modpost.c                 | 24 +++++++++++++++++++++++-
> 6 files changed, 80 insertions(+), 1 deletion(-)
>
>diff --git a/Documentation/ABI/stable/sysfs-module b/Documentation/ABI/stable/sysfs-module
>index 6272ae5fb366..a75d137e79f4 100644
>--- a/Documentation/ABI/stable/sysfs-module
>+++ b/Documentation/ABI/stable/sysfs-module
>@@ -32,3 +32,21 @@ Description:
> 		Note: If the module is built into the kernel, or if the
> 		CONFIG_MODULE_UNLOAD kernel configuration value is not enabled,
> 		this file will not be present.
>+
>+What:		/sys/module/MODULENAME/scmversion
>+Date:		November 2020
>+KernelVersion:	5.12
>+Contact:	Will McVicker <willmcvicker@google.com>
>+Description:	This read-only file will appear if modpost was supplied with an
>+		SCM version for the module. It can be enabled with the config
>+		MODULE_SCMVERSION. The SCM version is retrieved by
>+		scripts/setlocalversion, which means that the presence of this
>+		file depends on CONFIG_LOCALVERSION_AUTO=y. When read, the SCM
>+		version that the module was compiled with is returned. The SCM
>+		version is returned in the following format::
>+
>+		===
>+		Git:		g[a-f0-9]\+(-dirty)\?
>+		Mercurial:	hg[a-f0-9]\+(-dirty)\?
>+		Subversion:	svn[0-9]\+
>+		===
>diff --git a/include/linux/module.h b/include/linux/module.h
>index 7a0bcb5b1ffc..3b1612193cf9 100644
>--- a/include/linux/module.h
>+++ b/include/linux/module.h
>@@ -372,6 +372,7 @@ struct module {
> 	struct module_attribute *modinfo_attrs;
> 	const char *version;
> 	const char *srcversion;
>+	const char *scmversion;
> 	struct kobject *holders_dir;
>
> 	/* Exported symbols */
>diff --git a/init/Kconfig b/init/Kconfig
>index b77c60f8b963..3d9dac3c4e8f 100644
>--- a/init/Kconfig
>+++ b/init/Kconfig
>@@ -2131,6 +2131,20 @@ config MODULE_SRCVERSION_ALL
> 	  the version).  With this option, such a "srcversion" field
> 	  will be created for all modules.  If unsure, say N.
>
>+config MODULE_SCMVERSION
>+	bool "SCM version for modules"
>+	depends on LOCALVERSION_AUTO
>+	help
>+	  This enables the module attribute "scmversion" which can be used
>+	  by developers to identify the SCM version of a given module, e.g.
>+	  git sha1 or hg sha1. The SCM version can be queried by modinfo or
>+	  via the sysfs node: /sys/modules/MODULENAME/scmversion. This is
>+	  useful when the kernel or kernel modules are updated separately
>+	  since that causes the vermagic of the kernel and the module to
>+	  differ.
>+
>+	  If unsure, say N.
>+
> config MODULE_SIG
> 	bool "Module signature verification"
> 	select MODULE_SIG_FORMAT
>diff --git a/kernel/module.c b/kernel/module.c
>index 4bf30e4b3eaa..d0b359c7e9c9 100644
>--- a/kernel/module.c
>+++ b/kernel/module.c
>@@ -837,6 +837,7 @@ static struct module_attribute modinfo_##field = {                    \
>
> MODINFO_ATTR(version);
> MODINFO_ATTR(srcversion);
>+MODINFO_ATTR(scmversion);
>
> static char last_unloaded_module[MODULE_NAME_LEN+1];
>
>@@ -1298,6 +1299,7 @@ static struct module_attribute *modinfo_attrs[] = {
> 	&module_uevent,
> 	&modinfo_version,
> 	&modinfo_srcversion,
>+	&modinfo_scmversion,
> 	&modinfo_initstate,
> 	&modinfo_coresize,
> 	&modinfo_initsize,
>diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
>index f54b6ac37ac2..f1126b60adb7 100644
>--- a/scripts/Makefile.modpost
>+++ b/scripts/Makefile.modpost
>@@ -66,6 +66,7 @@ ifeq ($(KBUILD_EXTMOD),)
>
> input-symdump := vmlinux.symvers
> output-symdump := Module.symvers
>+module_srcpath := $(srctree)
>
> else
>
>@@ -77,6 +78,17 @@ src := $(obj)
> include $(if $(wildcard $(KBUILD_EXTMOD)/Kbuild), \
>              $(KBUILD_EXTMOD)/Kbuild, $(KBUILD_EXTMOD)/Makefile)
>
>+# Get the external module's source path. KBUILD_EXTMOD could either be an
>+# absolute path or relative path from $(srctree). This makes sure that we
>+# aren't using a relative path from a separate working directory (O= or
>+# KBUILD_OUTPUT) since that may not be the actual module's SCM project path.
>+# So check the path relative to $(srctree) first.
>+ifneq ($(realpath $(srctree)/$(KBUILD_EXTMOD) 2>/dev/null),)
>+	module_srcpath := $(srctree)/$(KBUILD_EXTMOD)
>+else
>+	module_srcpath := $(KBUILD_EXTMOD)
>+endif
>+
> # modpost option for external modules
> MODPOST += -e
>
>@@ -85,6 +97,16 @@ output-symdump := $(KBUILD_EXTMOD)/Module.symvers
>
> endif
>
>+ifeq ($(CONFIG_MODULE_SCMVERSION),y)
>+# Get the SCM version of the module. Sed verifies setlocalversion returns
>+# a proper revision based on the SCM type, e.g. git, mercurial, or svn.
>+module_scmversion := $(shell $(srctree)/scripts/setlocalversion $(module_srcpath) | \
>+	sed -n 's/.*-\(\(g\|hg\)[a-fA-F0-9]\+\(-dirty\)\?\|svn[0-9]\+\).*/\1/p')
>+ifneq ($(module_scmversion),)
>+MODPOST += -v$(module_scmversion)
>+endif
>+endif
>+
> # modpost options for modules (both in-kernel and external)
> MODPOST += \
> 	$(addprefix -i ,$(wildcard $(input-symdump))) \
>diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
>index d6c81657d695..489b65bc37de 100644
>--- a/scripts/mod/modpost.c
>+++ b/scripts/mod/modpost.c
>@@ -30,6 +30,8 @@ static int have_vmlinux = 0;
> static int all_versions = 0;
> /* If we are modposting external module set to 1 */
> static int external_module = 0;
>+#define MODULE_SCMVERSION_SIZE 64
>+static char module_scmversion[MODULE_SCMVERSION_SIZE];
> /* Only warn about unresolved symbols */
> static int warn_unresolved = 0;
> /* How a symbol is exported */
>@@ -2264,6 +2266,20 @@ static void add_intree_flag(struct buffer *b, int is_intree)
> 		buf_printf(b, "\nMODULE_INFO(intree, \"Y\");\n");
> }
>
>+/**
>+ * add_scmversion() - Adds the MODULE_INFO macro for the scmversion.
>+ * @b: Buffer to append to.
>+ *
>+ * This function fills in the module attribute `scmversion` for the kernel
>+ * module. This is useful for determining a given module's SCM version on
>+ * device via /sys/modules/<module>/scmversion and/or using the modinfo tool.
>+ */
>+static void add_scmversion(struct buffer *b)
>+{
>+	if (module_scmversion[0] != '\0')
>+		buf_printf(b, "\nMODULE_INFO(scmversion, \"%s\");\n", module_scmversion);
>+}
>+
> /* Cannot check for assembler */
> static void add_retpoline(struct buffer *b)
> {
>@@ -2546,7 +2562,7 @@ int main(int argc, char **argv)
> 	struct dump_list *dump_read_start = NULL;
> 	struct dump_list **dump_read_iter = &dump_read_start;
>
>-	while ((opt = getopt(argc, argv, "ei:mnT:o:awENd:")) != -1) {
>+	while ((opt = getopt(argc, argv, "ei:mnT:o:awENd:v:")) != -1) {
> 		switch (opt) {
> 		case 'e':
> 			external_module = 1;
>@@ -2584,6 +2600,11 @@ int main(int argc, char **argv)
> 		case 'd':
> 			missing_namespace_deps = optarg;
> 			break;
>+		case 'v':
>+			if (!optarg)
>+				fatal("'-v' requires an argument defining the SCM version.");
>+			strncpy(module_scmversion, optarg, sizeof(module_scmversion) - 1);
>+			break;
> 		default:
> 			exit(1);
> 		}
>@@ -2630,6 +2651,7 @@ int main(int argc, char **argv)
> 		add_depends(&buf, mod);
> 		add_moddevtable(&buf, mod);
> 		add_srcversion(&buf, mod);
>+		add_scmversion(&buf);
>
> 		sprintf(fname, "%s.mod.c", mod->name);
> 		write_if_changed(&buf, fname);
>-- 
>2.30.0.284.gd98b1dd5eaa7-goog
>