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e79024e0cf
Most x87 instruction implementations fail to raise the expected IEEE floating-point exceptions because they do nothing to convert the exception state from the softfloat machinery into the exception flags in the x87 status word. There is special-case handling of division to raise the divide-by-zero exception, but that handling is itself buggy: it raises the exception in inappropriate cases (inf / 0 and nan / 0, which should not raise any exceptions, and 0 / 0, which should raise "invalid" instead). Fix this by converting the floating-point exceptions raised during an operation by the softfloat machinery into exceptions in the x87 status word (passing through the existing fpu_set_exception function for handling related to trapping exceptions). There are special cases where some functions convert to integer internally but exceptions from that conversion are not always correct exceptions for the instruction to raise. There might be scope for some simplification if the softfloat exception state either could always be assumed to be in sync with the state in the status word, or could always be ignored at the start of each instruction and just set to 0 then; I haven't looked into that in detail, and it might run into interactions with the various ways the emulation does not yet handle trapping exceptions properly. I think the approach taken here, of saving the softfloat state, setting exceptions there to 0 and then merging the old exceptions back in after carrying out the operation, is conservatively safe Backports commit 975af797f1e04e4d1b1a12f1731141d3770fdbce from qemu |
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