• Matthias Maennich's avatar
    module: add support for symbol namespaces. · 8651ec01
    Matthias Maennich authored
    The EXPORT_SYMBOL_NS() and EXPORT_SYMBOL_NS_GPL() macros can be used to
    export a symbol to a specific namespace.  There are no _GPL_FUTURE and
    _UNUSED variants because these are currently unused, and I'm not sure
    they are necessary.
    
    I didn't add EXPORT_SYMBOL_NS() for ASM exports; this patch sets the
    namespace of ASM exports to NULL by default. In case of relative
    references, it will be relocatable to NULL. If there's a need, this
    should be pretty easy to add.
    
    A module that wants to use a symbol exported to a namespace must add a
    MODULE_IMPORT_NS() statement to their module code; otherwise, modpost
    will complain when building the module, and the kernel module loader
    will emit an error and fail when loading the module.
    
    MODULE_IMPORT_NS() adds a modinfo tag 'import_ns' to the module. That
    tag can be observed by the modinfo command, modpost and kernel/module.c
    at the time of loading the module.
    
    The ELF symbols are renamed to include the namespace with an asm label;
    for example, symbol 'usb_stor_suspend' in namespace USB_STORAGE becomes
    'usb_stor_suspend.USB_STORAGE'.  This allows modpost to do namespace
    checking, without having to go through all the effort of parsing ELF and
    relocation records just to get to the struct kernel_symbols.
    
    On x86_64 I saw no difference in binary size (compression), but at
    runtime this will require a word of memory per export to hold the
    namespace. An alternative could be to store namespaced symbols in their
    own section and use a separate 'struct namespaced_kernel_symbol' for
    that section, at the cost of making the module loader more complex.
    Co-developed-by: default avatarMartijn Coenen <maco@android.com>
    Signed-off-by: default avatarMartijn Coenen <maco@android.com>
    Reviewed-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    Signed-off-by: default avatarMatthias Maennich <maennich@google.com>
    Signed-off-by: default avatarJessica Yu <jeyu@kernel.org>
    8651ec01
export.h 2.15 KB