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13f60e80e1
Due to how gelf_update_sym*() requires an Elf_Data pointer, and how libelf keeps Elf_Data in a linked list per section, elf_update_symbol() ends up having to iterate this list on each update to find the correct Elf_Data for the index'ed symbol. By allocating one Elf_Data per new symbol, the list grows per new symbol, giving an effective O(n^2) insertion time. This is obviously bloody terrible. Therefore over-allocate the Elf_Data when an extention is needed. Except it turns out libelf disregards Elf_Scn::sh_size in favour of the sum of Elf_Data::d_size. IOW it will happily write out all the unused space and fill it with: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND entries (aka zeros). Which obviously violates the STB_LOCAL placement rule, and is a general pain in the backside for not being the desired behaviour. Manually fix-up the Elf_Data size to avoid this problem before calling elf_update(). This significantly improves performance when adding a significant number of symbols. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Tested-by: Yujie Liu <yujie.liu@intel.com> Link: https://lkml.kernel.org/r/20221028194453.461658986@infradead.org
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.