Messages in this thread | | | Date | Wed, 9 Apr 2008 19:15:34 -0400 | From | Mathieu Desnoyers <> | Subject | Re: [patch 13/17] Immediate Values - x86 Optimization (updated) |
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* H. Peter Anvin (hpa@zytor.com) wrote: > Mathieu Desnoyers wrote: >> Hrm, since even the nmi-safe version supports REX-prefixed instructions, >> there is no need for an =q constraint on single-byte immediate values >> anymore. (thanks to your "discard" section used in the nmi-safe version) > > WRONG! > > Using =r for single-byte values is incorrect for 32-bit code -- that would > permit %spl, %bpl, %sil, %dil which are illegal in 32-bit mode. That is not > the incorrect bit, it's the description that is confused. > > -hpa
Ah, right. I remembered there was something that made us use =q, but could not remember what. I'll describe it correctly.
Therefore, this updated patch is bogus. The original one was ok, given that we change the header to :
Immediate Values - x86 Optimization
x86 optimization of the immediate values which uses a movl with code patching to set/unset the value used to populate the register used as variable source.
Note : a movb needs to get its value froma =q constraint.
Quoting "H. Peter Anvin" <hpa@zytor.com>
Using =r for single-byte values is incorrect for 32-bit code -- that would permit %spl, %bpl, %sil, %dil which are illegal in 32-bit mode.
Changelog: - Use text_poke_early with cr0 WP save/restore to patch the bypass. We are doing non atomic writes to a code region only touched by us (nobody can execute it since we are protected by the imv_mutex). - Put imv_set and _imv_set in the architecture independent header. - Use $0 instead of %2 with (0) operand. - Add x86_64 support, ready for i386+x86_64 -> x86 merge. - Use asm-x86/asm.h. - Bugfix : 8 bytes 64 bits immediate value was declared as "4 bytes" in the immediate structure. - Change the immediate.c update code to support variable length opcodes. - Vastly simplified, using a busy looping IPI with interrupts disabled. Does not protect against NMI nor MCE. - Pack the __imv section. Use smallest types required for size (char). - Use imv_* instead of immediate_*.
Mathieu
-- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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