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6c480f2221
Address two issues: - it no longer hard requires single byte NOP runs - now it accepts any NOP and NOPL encoded instruction (but not the more complicated 32bit NOPs). - it writes a single 'instruction' replacement. Specifically, ORC unwinder relies on the tail NOP of an alternative to be a single instruction. In particular, it relies on the inner bytes not being executed. Once the max supported NOP length has been reached (currently 8, could easily be extended to 11 on x86_64), switch to JMP.d8 and INT3 padding to achieve the same result. Objtool uses this guarantee in the analysis of alternative/overlapping CFI state for the ORC unwinder data. Every instruction edge gets a CFI state and the more instructions the larger the chance of conflicts. [ bp: - Add a comment over add_nop() to explain why it does it this way - Make add_nops() PARAVIRT only as it is used solely there now ] Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de> Link: https://lore.kernel.org/r/20230208171431.373412974@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.