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authorMatthias Maennich <maennich@google.com>2019-09-06 11:32:27 +0100
committerJessica Yu <jeyu@kernel.org>2019-09-10 10:30:17 +0200
commit8651ec01daedad26290f76beeb4736f9d2da4b87 (patch)
treeaddd8a0c1a51b5000c96218a1b349fde30ff4f29 /scripts/export_report.pl
parented13fc33f763035a7c290f11c7111877c3a5daab (diff)
module: add support for symbol namespaces.
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: Martijn Coenen <maco@android.com> Signed-off-by: Martijn Coenen <maco@android.com> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Matthias Maennich <maennich@google.com> Signed-off-by: Jessica Yu <jeyu@kernel.org>
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