linux-kernel - Re: [PATCH] modpost: move the namespace field in Module.symvers last

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Message-ID: <20200305085948.GD119445@google.com>
Date:   Thu, 5 Mar 2020 08:59:48 +0000
From:   Matthias Maennich <maennich@...gle.com>
To:     Jessica Yu <jeyu@...nel.org>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Lucas De Marchi <lucas.de.marchi@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] modpost: move the namespace field in Module.symvers last

Hi Jessica!
Thanks for working on this!

On Wed, Mar 04, 2020 at 06:03:45PM +0100, Jessica Yu wrote:
>In order to preserve backwards compatability with kmod tools, we have to
>move the namespace field in Module.symvers last, as the depmod -e -E
>option looks at the first three fields in Module.symvers to check symbol
>versions (and it's expected they stay in the original order of crc,
>symbol, module).
>
>Fixes: cb9b55d21fe0 ("modpost: add support for symbol namespaces")
>Cc: stable@...r.kernel.org

Please note, this patch did not actually go to stable@.

>Signed-off-by: Jessica Yu <jeyu@...nel.org>
>---
> Documentation/kbuild/modules.rst |  4 ++--
> scripts/export_report.pl         |  2 +-
> scripts/mod/modpost.c            | 24 ++++++++++++------------
> 3 files changed, 15 insertions(+), 15 deletions(-)
>
>diff --git a/Documentation/kbuild/modules.rst b/Documentation/kbuild/modules.rst
>index 69fa48ee93d6..e0b45a257f21 100644
>--- a/Documentation/kbuild/modules.rst
>+++ b/Documentation/kbuild/modules.rst
>@@ -470,9 +470,9 @@ build.
>
> 	The syntax of the Module.symvers file is::
>
>-	<CRC>       <Symbol>          <Namespace>  <Module>                         <Export Type>
>+	<CRC>       <Symbol>         <Module>                         <Export Type>     <Namespace>
>
>-	0xe1cc2a05  usb_stor_suspend  USB_STORAGE  drivers/usb/storage/usb-storage  EXPORT_SYMBOL_GPL
>+	0xe1cc2a05  usb_stor_suspend drivers/usb/storage/usb-storage  EXPORT_SYMBOL_GPL USB_STORAGE
>
> 	The fields are separated by tabs and values may be empty (e.g.
> 	if no namespace is defined for an exported symbol).
>diff --git a/scripts/export_report.pl b/scripts/export_report.pl
>index 548330e8c4e7..feb3d5542a62 100755
>--- a/scripts/export_report.pl
>+++ b/scripts/export_report.pl
>@@ -94,7 +94,7 @@ if (defined $opt{'o'}) {
> #
> while ( <$module_symvers> ) {
> 	chomp;
>-	my (undef, $symbol, $namespace, $module, $gpl) = split('\t');
>+	my (undef, $symbol, $module, $gpl, $namespace) = split('\t');
> 	$SYMBOL { $symbol } =  [ $module , "0" , $symbol, $gpl];
> }
> close($module_symvers);
>diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
>index 7edfdb2f4497..6ab235354f36 100644
>--- a/scripts/mod/modpost.c
>+++ b/scripts/mod/modpost.c
>@@ -2427,7 +2427,7 @@ static void write_if_changed(struct buffer *b, const char *fname)
> }
>
> /* parse Module.symvers file. line format:
>- * 0x12345678<tab>symbol<tab>module[[<tab>export]<tab>something]
>+ * 0x12345678<tab>symbol<tab>module<tab>export<tab>namespace
>  **/
> static void read_dump(const char *fname, unsigned int kernel)
> {
>@@ -2440,7 +2440,7 @@ static void read_dump(const char *fname, unsigned int kernel)
> 		return;
>
> 	while ((line = get_next_line(&pos, file, size))) {
>-		char *symname, *namespace, *modname, *d, *export, *end;
>+		char *symname, *namespace, *modname, *d, *export;
> 		unsigned int crc;
> 		struct module *mod;
> 		struct symbol *s;
>@@ -2448,16 +2448,16 @@ static void read_dump(const char *fname, unsigned int kernel)
> 		if (!(symname = strchr(line, '\t')))
> 			goto fail;
> 		*symname++ = '\0';
>-		if (!(namespace = strchr(symname, '\t')))
>-			goto fail;
>-		*namespace++ = '\0';
>-		if (!(modname = strchr(namespace, '\t')))
>+		if (!(modname = strchr(symname, '\t')))
> 			goto fail;
> 		*modname++ = '\0';
>-		if ((export = strchr(modname, '\t')) != NULL)
>-			*export++ = '\0';
>-		if (export && ((end = strchr(export, '\t')) != NULL))
>-			*end = '\0';
>+		if (!(export = strchr(modname, '\t')))
>+			goto fail;
>+		*export++ = '\0';
>+		if (!(namespace = strchr(export, '\t')))

As mentioned below, we should probably treat namespace as an optional
field. Then this needs adjusting to handle that case. Similar to how
optional cases were handled before.

>+			goto fail;
>+		*namespace++ = '\0';
>+
> 		crc = strtoul(line, &d, 16);
> 		if (*symname == '\0' || *modname == '\0' || *d != '\0')
> 			goto fail;
>@@ -2508,9 +2508,9 @@ static void write_dump(const char *fname)
> 				namespace = symbol->namespace;
> 				buf_printf(&buf, "0x%08x\t%s\t%s\t%s\t%s\n",

This creates trailing tabs for symbols without namespace. If we treat
'namespace' as an optional field, we should probably make the tab
conditional as well? What do you think?

Cheers,
Matthias

> 					   symbol->crc, symbol->name,
>-					   namespace ? namespace : "",
> 					   symbol->module->name,
>-					   export_str(symbol->export));
>+					   export_str(symbol->export),
>+					   namespace ? namespace : "");
> 			}
> 			symbol = symbol->next;
> 		}
>-- 
>2.16.4
>