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x86-emu : i486/i686 instructions emulation for low-end processors
This patch allows user space programs compiled for 486 to run on a 386
without crashing with a SIGILL. As any emulation, performance will be
very low, but since these instruction are not often used, this might
not hurt. The i686 emulation can have an impact though, because the
CMOV instructions are often used in optimized code. Note that this
patch must not be used on SMP systems and might even be at risk on
hyperthreaded code.
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| Initial date: | 2002/06/30 |
| Last update: | 2004/03/04 |
| Description: | i486/i686 instructions emulation for low-end processors |
| Author(s): | Willy Tarreau |
| Abstract: | This patch allows user space programs compiled for 486 to run on a 386
without crashing with a SIGILL. As any emulation, performance will be
very low, but since these instruction are not often used, this might
not hurt. The i686 emulation can have an impact though, because the
CMOV instructions are often used in optimized code. Note that this
patch must not be used on SMP systems and might even be at risk on
hyperthreaded code.
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Notes
The following i486 instructions are emulated on i386 :
- bswap (does the same as htonl())
- cmpxchg (used in multi-threading, mutex locking)
- xadd (rarely used)
The CMOV emulation from the i686 instruction set is emulated on 386,
486, Pentium, AmdK6, and VIA Eden. It is relatively slow (about 1µs
on a k6/450) and should be emulated only for compatibility.
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(C) Willy Tarreau - 2008-06-01