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2dbbca9be4
Objtool uses an arbitrary rule for INSN_SYSCALL and INSN_SYSRET that almost works by accident: if it's in a function, control flow continues after the instruction, otherwise it terminates. That behavior should instead be based on the semantics of the underlying instruction. Change INSN_SYSCALL to always preserve control flow and INSN_SYSRET to always terminate it. The changed semantic for INSN_SYSCALL requires a tweak to the !CONFIG_IA32_EMULATION version of xen_entry_SYSCALL_compat(). In Xen, SYSCALL is a hypercall which usually returns. But in this case it's a hypercall to IRET which doesn't return. Add UD2 to tell objtool to terminate control flow, and to prevent undefined behavior at runtime. Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Reviewed-by: Juergen Gross <jgross@suse.com> # for the Xen part Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: https://lore.kernel.org/r/19453dfe9a0431b7f016e9dc16d031cad3812a50.1744095216.git.jpoimboe@kernel.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 reStructuredText 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.