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745a14cc26
This adds a system call on 64-bit platforms for switching between little-endian and big-endian modes that is much faster than doing a prctl call. This system call is handled as a special case right at the start of the system call entry code, and because it is a special case, it uses a system call number which is out of the range of normal system calls, namely 0x1ebe. Measurements with lmbench on a 4.2GHz POWER6 showed no measurable change in the speed of normal system calls with this patch. Switching endianness with this new system call takes around 60ns on a 4.2GHz POWER6, compared with around 300ns to switch endian mode with a prctl. This can provide a significant performance advantage for emulators for little-endian architectures that want to switch between big-endian and little-endian mode frequently, e.g. because they are generating instructions sequences on the fly and they want to run those sequences in little-endian mode. The other thing about this system call is that it doesn't clobber as many registers as a normal system call. It only clobbers r12. Signed-off-by: Paul Mackerras <paulus@samba.org> |
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| math-emu | ||
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| xmon | ||
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