https://sourceware.org/bugzilla/show_bug.cgi?id=30120
Bug ID: 30120
Summary: x87: fucomp assembled as fucom
Product: binutils
Version: 2.41 (HEAD)
Status: NEW
Severity: normal
Priority: P2
Component: gas
Assignee: unassigned at sourceware dot org
Reporter: matz at suse dot de
Target Milestone: ---
% cat asm.s
fucomp %st(1)
% ./gas/as-new asm.s && objdump -d a.out
...
0000000000000000 <.text>:
0: dd e1 fucom %st(1)
It should be 'dd e9 fucomp %st(1)'. This results in the x87 sometimes not
be popped and wrong results. (GCC generates fucom{i,}p sometimes, of course).
Possibly some other mnemonics are affected as well, where there are popping (or
twice-popping) and non-popping variants, but this is one that effectively made
glibc miscompiled (in the sqrt implementation that uses 'isless').
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