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Implement memcmp(), memcpy(), and memset() to override the compiler's
built-in versions in order to guarantee that the compiler won't generate
out-of-line calls to external functions via the PLT. This allows the
helpers to be safely used in guest code, as KVM selftests don't support
dynamic loading of guest code.
Steal the implementations from the kernel's generic versions, sans the
optimizations in memcmp() for unaligned accesses.
Put the utilities in a separate compilation unit and build with
-ffreestanding to fudge around a gcc "feature" where it will optimize
memset(), memcpy(), etc... by generating a recursive call. I.e. the
compiler optimizes itself into infinite recursion. Alternatively, the
individual functions could be tagged with
optimize("no-tree-loop-distribute-patterns"), but using "optimize" for
anything but debug is discouraged, and Linus NAK'd the use of the flag
in the kernel proper[*].
https://lore.kernel.org/lkml/CAHk-=wik-oXnUpfZ6Hw37uLykc-_P0Apyn2XuX-odh-3Nzop8w@mail.gmail.com
Cc: Andrew Jones <[email protected]>
Cc: Anup Patel <[email protected]>
Cc: Atish Patra <[email protected]>
Cc: Christian Borntraeger <[email protected]>
Cc: Janosch Frank <[email protected]>
Cc: Claudio Imbrenda <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
Message-Id: <[email protected]>
Reviewed-by: Andrew Jones <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>
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