[Valgrind-developers] ppc instruction decoder

[Florian K. <fl...@ei...>]

The ppc instruction decoder generates misleading error messages.
This happens for instance for an altivec insn when the host does not
have altivec support. E.g.

disInstr(ppc): declined to decode an AltiVec insn.
disInstr(ppc): unhandled instruction: 0x7E8029CE

This is misleading and conceptually wrong. Decoding an insn and
generating code for it are two different issues that need to be
distinguished.
If the insn cannot be decoded, a decoder failure should be reported.
If we cannot generate code for the insn due to insufficient host
capabilities, an emulation failure should be reported.
This is what is done for s390. If you're interested search for
emulation_failure in guest_s390_toIR.c

Yesterday I was mislead and marked a bunch of BZ's related to
unsupported altivec insns as fixed. I should probably add a clarifying
comment that the insn is only supported on a host with altivec
capabilities. But I'm not sure that assumption is correct. Is it ?

   Florian