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Date:   Wed, 28 Aug 2019 11:43:26 +0200
From:   Jessica Yu <jeyu@kernel.org>
To:     Matthias Maennich <maennich@google.com>
Cc:     linux-kernel@vger.kernel.org, kernel-team@android.com,
        arnd@arndb.de, geert@linux-m68k.org, gregkh@linuxfoundation.org,
        hpa@zytor.com, joel@joelfernandes.org,
        kstewart@linuxfoundation.org, linux-arch@vger.kernel.org,
        linux-kbuild@vger.kernel.org, linux-m68k@lists.linux-m68k.org,
        linux-modules@vger.kernel.org, linux-scsi@vger.kernel.org,
        linux-usb@vger.kernel.org, lucas.de.marchi@gmail.com,
        maco@android.com, maco@google.com, michal.lkml@markovi.net,
        mingo@redhat.com, oneukum@suse.com, pombredanne@nexb.com,
        sam@ravnborg.org, sspatil@google.com, stern@rowland.harvard.edu,
        tglx@linutronix.de, usb-storage@lists.one-eyed-alien.net,
        x86@kernel.org, yamada.masahiro@socionext.com
Subject: Re: [PATCH v3 04/11] modpost: add support for symbol namespaces
Message-ID: <20190828094325.GA25048@linux-8ccs>
References: <20190813121733.52480-1-maennich@google.com>
 <20190821114955.12788-1-maennich@google.com>
 <20190821114955.12788-5-maennich@google.com>
 <20190826162138.GA31739@linux-8ccs>
 <20190827144117.GB102829@google.com>
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+++ Matthias Maennich [27/08/19 15:41 +0100]:
>On Mon, Aug 26, 2019 at 06:21:38PM +0200, Jessica Yu wrote:
>>+++ Matthias Maennich [21/08/19 12:49 +0100]:
>>>Add support for symbols that are exported into namespaces. For that,
>>>extract any namespace suffix from the symbol name. In addition, emit a
>>>warning whenever a module refers to an exported symbol without
>>>explicitly importing the namespace that it is defined in. This patch
>>>consistently adds the namespace suffix to symbol names exported into
>>>Module.symvers.
>>>
>>>Example warning emitted by modpost in case of the above violation:
>>>
>>>WARNING: module ums-usbat uses symbol usb_stor_resume from namespace
>>>USB_STORAGE, but does not import it.
>>>
>>>Co-developed-by: Martijn Coenen <maco@android.com>
>>>Signed-off-by: Martijn Coenen <maco@android.com>
>>>Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
>>>Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>>>Signed-off-by: Matthias Maennich <maennich@google.com>
>>>---
>>>scripts/mod/modpost.c | 91 +++++++++++++++++++++++++++++++++++++------
>>>scripts/mod/modpost.h |  7 ++++
>>>2 files changed, 87 insertions(+), 11 deletions(-)
>>>
>>>diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
>>>index f277e116e0eb..538bb24ffee3 100644
>>>--- a/scripts/mod/modpost.c
>>>+++ b/scripts/mod/modpost.c
>>>@@ -164,6 +164,7 @@ struct symbol {
>>>	struct module *module;
>>>	unsigned int crc;
>>>	int crc_valid;
>>>+	const char *namespace;
>>>	unsigned int weak:1;
>>>	unsigned int vmlinux:1;    /* 1 if symbol is defined in vmlinux */
>>>	unsigned int kernel:1;     /* 1 if symbol is from kernel
>>>@@ -233,6 +234,37 @@ static struct symbol *find_symbol(const char *name)
>>>	return NULL;
>>>}
>>>
>>>+static bool contains_namespace(struct namespace_list *list,
>>>+			       const char *namespace)
>>>+{
>>>+	struct namespace_list *ns_entry;
>>>+
>>>+	for (ns_entry = list; ns_entry != NULL; ns_entry = ns_entry->next)
>>>+		if (strcmp(ns_entry->namespace, namespace) == 0)
>>>+			return true;
>>>+
>>>+	return false;
>>>+}
>>>+
>>>+static void add_namespace(struct namespace_list **list, const char *namespace)
>>>+{
>>>+	struct namespace_list *ns_entry;
>>>+
>>>+	if (!contains_namespace(*list, namespace)) {
>>>+		ns_entry = NOFAIL(malloc(sizeof(struct namespace_list) +
>>>+					 strlen(namespace) + 1));
>>>+		strcpy(ns_entry->namespace, namespace);
>>>+		ns_entry->next = *list;
>>>+		*list = ns_entry;
>>>+	}
>>>+}
>>>+
>>>+static bool module_imports_namespace(struct module *module,
>>>+				     const char *namespace)
>>>+{
>>>+	return contains_namespace(module->imported_namespaces, namespace);
>>>+}
>>>+
>>>static const struct {
>>>	const char *str;
>>>	enum export export;
>>>@@ -312,6 +344,22 @@ static enum export export_from_sec(struct elf_info *elf, unsigned int sec)
>>>		return export_unknown;
>>>}
>>>
>>>+static const char *sym_extract_namespace(const char **symname)
>>>+{
>>>+	size_t n;
>>>+	char *dupsymname;
>>>+
>>>+	n = strcspn(*symname, ".");
>>>+	if (n < strlen(*symname) - 1) {
>>>+		dupsymname = NOFAIL(strdup(*symname));
>>>+		dupsymname[n] = '\0';
>>>+		*symname = dupsymname;
>>>+		return dupsymname + n + 1;
>>>+	}
>>>+
>>>+	return NULL;
>>>+}
>>>+
>>>/**
>>>* Add an exported symbol - it may have already been added without a
>>>* CRC, in this case just update the CRC
>>>@@ -319,16 +367,18 @@ static enum export export_from_sec(struct elf_info *elf, unsigned int sec)
>>>static struct symbol *sym_add_exported(const char *name, struct module *mod,
>>>				       enum export export)
>>>{
>>>-	struct symbol *s = find_symbol(name);
>>>+	const char *symbol_name = name;
>>>+	const char *namespace = sym_extract_namespace(&symbol_name);
>>>+	struct symbol *s = find_symbol(symbol_name);
>>>
>>>	if (!s) {
>>>-		s = new_symbol(name, mod, export);
>>>+		s = new_symbol(symbol_name, mod, export);
>>>+		s->namespace = namespace;
>>>	} else {
>>>		if (!s->preloaded) {
>>>-			warn("%s: '%s' exported twice. Previous export "
>>>-			     "was in %s%s\n", mod->name, name,
>>>-			     s->module->name,
>>>-			     is_vmlinux(s->module->name) ?"":".ko");
>>>+			warn("%s: '%s' exported twice. Previous export was in %s%s\n",
>>>+			     mod->name, symbol_name, s->module->name,
>>>+			     is_vmlinux(s->module->name) ? "" : ".ko");
>>>		} else {
>>>			/* In case Module.symvers was out of date */
>>>			s->module = mod;
>>>@@ -1943,6 +1993,7 @@ static void read_symbols(const char *modname)
>>>	const char *symname;
>>>	char *version;
>>>	char *license;
>>>+	char *namespace;
>>>	struct module *mod;
>>>	struct elf_info info = { };
>>>	Elf_Sym *sym;
>>>@@ -1974,6 +2025,12 @@ static void read_symbols(const char *modname)
>>>		license = get_next_modinfo(&info, "license", license);
>>>	}
>>>
>>>+	namespace = get_modinfo(&info, "import_ns");
>>>+	while (namespace) {
>>>+		add_namespace(&mod->imported_namespaces, namespace);
>>>+		namespace = get_next_modinfo(&info, "import_ns", namespace);
>>>+	}
>>>+
>>>	for (sym = info.symtab_start; sym < info.symtab_stop; sym++) {
>>>		symname = remove_dot(info.strtab + sym->st_name);
>>>
>>>@@ -2118,6 +2175,13 @@ static int check_exports(struct module *mod)
>>>			basename++;
>>>		else
>>>			basename = mod->name;
>>>+
>>>+		if (exp->namespace &&
>>>+		    !module_imports_namespace(mod, exp->namespace)) {
>>>+			warn("module %s uses symbol %s from namespace %s, but does not import it.\n",
>>>+			     basename, exp->name, exp->namespace);
>>>+		}
>>>+
>>>		if (!mod->gpl_compatible)
>>>			check_for_gpl_usage(exp->export, basename, exp->name);
>>>		check_for_unused(exp->export, basename, exp->name);
>>>@@ -2395,16 +2459,21 @@ static void write_dump(const char *fname)
>>>{
>>>	struct buffer buf = { };
>>>	struct symbol *symbol;
>>>+	const char *namespace;
>>>	int n;
>>>
>>>	for (n = 0; n < SYMBOL_HASH_SIZE ; n++) {
>>>		symbol = symbolhash[n];
>>>		while (symbol) {
>>>-			if (dump_sym(symbol))
>>>-				buf_printf(&buf, "0x%08x\t%s\t%s\t%s\n",
>>>-					symbol->crc, symbol->name,
>>>-					symbol->module->name,
>>>-					export_str(symbol->export));
>>>+			if (dump_sym(symbol)) {
>>>+				namespace = symbol->namespace;
>>>+				buf_printf(&buf, "0x%08x\t%s%s%s\t%s\t%s\n",
>>>+					   symbol->crc, symbol->name,
>>>+					   namespace ? "." : "",
>>>+					   namespace ? namespace : "",
>>
>>I think it might be cleaner to just have namespace be a separate
>>field in Module.symvers, rather than appending a dot and the
>>namespace at the end of a symbol name. Maybe something like
>>
>>  <crc> <symbol_name> <namespace> <module>
>>
>>For symbols without a namespace, we could just have "", with all
>>fields delimited by tabs. This is just a stylistic suggestion, what do
>>you think?
>
>I thought of something like that initially, but did not do it to not
>break users of this file. But as I am anyway breaking users by changing
>the symbol name into symbol.NS, I might as well do it as you suggested.
>Since read_dump() also knew already how to extract the namespaces from
>symbol.NS, it had already worked without a change to the reading code
>of modpost. Are there any other consumers of Module.symvers that we
>should be aware of?

Maybe we can ease any possible breakage caused by the new format by
putting the namespace column last? Then the first 4 fields crc,
symbol, module, export type will remain in the same order, with
namespace last. In-tree, I think we would need to update
scripts/export_report.pl.

kmod is likely to be affected too - Lucas, would the addition of a new
field (in the order described above) in Module.symvers break any kmod tools?

Thanks,

Jessica