add Linux kernel symbol namespace support

add Linux kernel symbol namespace support

Bug 28954 - add Linux Kernel symbol namespace support

Each Linux kernel symbol can be exported to a specified named
namespace or left in the global (nameless) namespace.

One complexity is that the symbol values which identify a string in
the __ksymtab_strings section must be interpretated differently for
vmlinux and .ko loadable modules as the former has a fixed load
address but the latter are relocatable. For vmlinux, the section base
address needs to be subtracted to obtain a section-relative offset.

The global namespace is explicitly represented as the empty string, at
least when it comes to the value of __kstrtabns_FOO symbols, but the
common interpretation is that such symbols lack an export namespace.

I would rather not have to make use of "empty implies missing" in many
places, so the code here represents namespace as optional<string> and
only the symtab reader cares about empty strings in __ksymtab_strings.

	* include/abg-ir.h (elf_symbol::elf_symbol): Add ns argument.
	(elf_symbol::create): Add ns argument.
	(elf_symbol::get_namespace): Declare new function.
	(elf_symbol::set_namespace): Declare new function.
	and set_namespace.
	* src/abg-comp-filter.cc (namespace_changed): Define new
	helper functions.
	(categorize_harmful_diff_node): Also call namespace_changed().
	* src/abg-ir.cc (elf_symbol::priv): Add namespace_ member.
	(elf_symbol::priv::priv): Add namespace_ to initialisers.
	(elf_symbol::elf_symbol): Take new ns argument and pass it to
	priv constructor.
	(elf_symbol::create): Take new ns argument and pass it to
	elf_symbol constructor.
	(elf_symbol::get_namespace): Define new function.
	(elf_symbol::set_namespace): Define new function.
	* src/abg-reader.cc (build_elf_symbol): If namespace
	attribute is present, set symbol namespace.
	* src/abg-reporter-priv.cc (maybe_report_diff_for_symbol): If
	symbol namespaces differ, report this.
	* src/abg-symtab-reader.cc (symtab::load): Get ELF header to
	distinguish vmlinux from .ko. Try to get __ksymtab_strings
	metadata and data. Use these to look up __kstrtabns_FOO
	namespace entries. Set symbol namespace where found.
	* src/abg-writer.cc (write_elf_symbol): Emit namespace
	attribute, if symbol has a namespace.
	* tests/data/Makefile.am: Add new test files.
	* tests/data/test-abidiff/test-namespace-0.xml: New test file.
	* tests/data/test-abidiff/test-namespace-1.xml: Likewise
	* tests/data/test-abidiff/test-namespace-report.txt: Likewise.
	* tests/test-abidiff.cc: Add new test case.

Reviewed-by: Matthias Maennich <maennich@google.com>
Signed-off-by: Giuliano Procida <gprocida@google.com>