Re: [PATCH] depmod: account for new namespace field in Module.symvers (for kernel versions >= 5.4)

[Lucas De Marchi <lucas.de.marchi@gmail.com>]

On Fri, Feb 21, 2020 at 8:53 AM Jessica Yu <jeyu@kernel.org> wrote:
>
> depmod -e -E is broken for kernel versions >= 5.4, because a new
> namespace field was added to Module.symvers. Each line is tab delimited
> with 5 fields in total. E.g.,
>
>         0xb352177e\tfind_first_bit\tnamespace\tvmlinux\tEXPORT_SYMBOL
>
> When a symbol doesn't have a namespace, then the namespace field is empty:
>
>         0xb352177e\tfind_first_bit\t\tvmlinux\tEXPORT_SYMBOL

Why is namespace added in the *middle*? We remember we specifically
talked about compatibility back when this was added. Why is it not at
the end so tools that don't know about namespace don't stop working?

Lucas De Marchi

>
> Fix up depmod_load_symvers() so it finds the crc, symbol, and module
> ("where") fields correctly. Since there can be empty fields, strsep() is
> used instead of strtok(), since strtok() cannot handle empty fields
> (i.e., two delimiters in succession).
>
> Signed-off-by: Jessica Yu <jeyu@kernel.org>
> ---
>
> Hi,
>
> I was not sure what the best way of determining the symvers format was. I
> guess counting delimiters isn't the prettiest way, but if anyone has a
> better idea, let me know. Thanks!
>
>  tools/depmod.c | 35 ++++++++++++++++++++++++++++++-----
>  1 file changed, 30 insertions(+), 5 deletions(-)
>
> diff --git a/tools/depmod.c b/tools/depmod.c
> index fbbce10..c5b9612 100644
> --- a/tools/depmod.c
> +++ b/tools/depmod.c
> @@ -2577,7 +2577,9 @@ static int depmod_load_symvers(struct depmod *depmod, const char *filename)
>  {
>         char line[10240];
>         FILE *fp;
> -       unsigned int linenum = 0;
> +       unsigned int linenum = 0, cnt = 0;
> +       bool uses_namespaces = false;
> +       char *ptr;
>
>         fp = fopen(filename, "r");
>         if (fp == NULL) {
> @@ -2587,7 +2589,26 @@ static int depmod_load_symvers(struct depmod *depmod, const char *filename)
>         }
>         DBG("load symvers: %s\n", filename);
>
> -       /* eg. "0xb352177e\tfind_first_bit\tvmlinux\tEXPORT_SYMBOL" */
> +       /*
> +        * First, check for >=5.4 Module.symvers format:
> +        * "0xb352177e\tfind_first_bit\tnamespace\tvmlinux\tEXPORT_SYMBOL"
> +        * If there are 5 fields (4 tabs), assume we're using the new format.
> +        */
> +       fgets(line, sizeof(line), fp);
> +       ptr = line;
> +       while ((ptr = strchr(ptr, '\t')) != NULL) {
> +               cnt++;
> +               ptr++;
> +       }
> +       if (cnt > 3)
> +               uses_namespaces = true;
> +       rewind(fp);
> +
> +       /*
> +        * eg. "0xb352177e\tfind_first_bit\tvmlinux\tEXPORT_SYMBOL"
> +        * Or if kernel version >=5.4:
> +        * "0xb352177e\tfind_first_bit\tnamespace\tvmlinux\tEXPORT_SYMBOL"
> +        */
>         while (fgets(line, sizeof(line), fp) != NULL) {
>                 const char *ver, *sym, *where;
>                 char *verend;
> @@ -2595,9 +2616,13 @@ static int depmod_load_symvers(struct depmod *depmod, const char *filename)
>
>                 linenum++;
>
> -               ver = strtok(line, " \t");
> -               sym = strtok(NULL, " \t");
> -               where = strtok(NULL, " \t");
> +               ptr = (char *)line;
> +               ver = strsep(&ptr, "\t");
> +               sym = strsep(&ptr, "\t");
> +               if (uses_namespaces) /* skip namespace field */
> +                       strsep(&ptr, "\t");
> +               where = strsep(&ptr, "\t");
> +
>                 if (!ver || !sym || !where)
>                         continue;
>
> --
> 2.16.4
>


-- 
Lucas De Marchi