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Date:   Tue, 27 Aug 2019 15:41:17 +0100
From:   Matthias Maennich <maennich@google.com>
To:     Jessica Yu <jeyu@kernel.org>
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,
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        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,
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        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: <20190827144117.GB102829@google.com>
References: <20190813121733.52480-1-maennich@google.com>
 <20190821114955.12788-1-maennich@google.com>
 <20190821114955.12788-5-maennich@google.com>
 <20190826162138.GA31739@linux-8ccs>
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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?

>Regardless of the chosen format, I think we need to document how
>namespaces are represented in Documentation/kbuild/modules.rst, where
>it describes the Module.symvers format.

Agreed. I will update the documentation. It anyway needs an update.

Cheers,
Matthias

>>+					   symbol->module->name,
>>+					   export_str(symbol->export));
>>+			}
>>			symbol = symbol->next;
>>		}
>>	}
>>diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
>>index 8453d6ac2f77..9626bf3e7424 100644
>>--- a/scripts/mod/modpost.h
>>+++ b/scripts/mod/modpost.h
>>@@ -109,6 +109,11 @@ buf_printf(struct buffer *buf, const char *fmt, ...);
>>void
>>buf_write(struct buffer *buf, const char *s, int len);
>>
>>+struct namespace_list {
>>+	struct namespace_list *next;
>>+	char namespace[0];
>>+};
>>+
>>struct module {
>>	struct module *next;
>>	const char *name;
>>@@ -121,6 +126,8 @@ struct module {
>>	struct buffer dev_table_buf;
>>	char	     srcversion[25];
>>	int is_dot_o;
>>+	// Actual imported namespaces
>>+	struct namespace_list *imported_namespaces;
>>};
>>
>>struct elf_info {
>>-- 
>>2.23.0.rc1.153.gdeed80330f-goog
>>