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We learned the hard way that some K8 processors also lack SAHF instruction. All K8 processors have to be switched to PTA_NO_SAHF, but the support can still be detected with -march=native.
--cut here-- 110 SAHF/LAHF Extended Feature Flag Defaults to Incorrect Value
The Extended Feature Flag bit defined for SAHF and LAHF instruction support in 64-bit mode is ECX[0]. However some processors that support the feature incorrectly return it as zero.
The operating system will not see the feature flag and therefore the extended feature will not be used.
For processors which support the feature (as determined by the processor revision ID), BIOS should write a one to:
Yes --cut here--
* config/i386/i386.c (override_options): Add PTA_NO_SAHF to k8, opteron, athlon-64 and athlon-fx processor_alias_table entries.
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i386-amd-no-sahf.diff
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