[Bug default/28954] add Linux Kernel symbol namespace support

[maennich at android dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28954

Matthias Maennich <maennich at android dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |maennich at android dot com

--- Comment #4 from Matthias Maennich <maennich at android dot com> ---
The namespaces are not part of the linkage name as that would confuse linkers,
loaders and external tools (and would also break some).

Instead the namespace is embedded in the ksymtab along with a MODVERSION CRC.
The ksymtab is basically an array of structs (struct kernel_symbol) that is
referred to from the symtab by the __ksymtab__<symbol> entries.

At module load time, every required symbol of a module is looked up in the list
of existing symbols (largely coming from vmlinux, and possibly from another
module) and loading is denied if the symbol has an attached namespace AND the
module does not declare the namespace as imported. (similarly loading is denied
upon a mismatch of the CRCs). 

Hence, the ABI breakage happens if the exported symbol newly has a namespace
attached while the consuming module does not (yet) declare the import of said
namespace.

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