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r13 in the kernel


while debugging lock_stubs.S I realized that r13 is always assumed to
contain the thread-id.

Is it really safe to do so? IIRC the V.4-ABI defines r13 as small data base
register, but when small data is not used it should be a normal
non-volatile register, like r14 - r31.
The kernel is compiled with -msdata=none.

What makes you sure that gcc's code generator wouldn't use r13 for storing
non-volatile data during a function?

Frank Wille

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