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[Bug gas/30120] x87: fucomp assembled as fucom


From: matz at suse dot de
Subject: [Bug gas/30120] x87: fucomp assembled as fucom
Date: Mon, 13 Feb 2023 16:56:28 +0000

https://sourceware.org/bugzilla/show_bug.cgi?id=30120

--- Comment #2 from Michael Matz <matz at suse dot de> ---
Came in with bd7828084 "x86: use ModR/M for FPU insns with operands".

The proper Reg field of ModRM for the popping variant of fucom is '5' not '4'.
So this:

--- a/opcodes/i386-opc.tbl
+++ b/opcodes/i386-opc.tbl
@@ -651,7 +651,7 @@ fcompp, 0xded9, FP, NoSuf, {}
 fucom, 0xdd/4, i387, Modrm|NoSuf, { FloatReg }
 // alias for fucom %st(1)
 fucom, 0xdde1, i387, NoSuf, {}
-fucomp, 0xdd/4, i387, Modrm|NoSuf, { FloatReg }
+fucomp, 0xdd/5, i387, Modrm|NoSuf, { FloatReg }
 // alias for fucomp %st(1)
 fucomp, 0xdde9, i387, NoSuf, {}
 fucompp, 0xdae9, i387, NoSuf, {}

(didn't check the other insns touched by the patch)

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