[Bug binutils/15229] New: objdump -d allows invalid avx2 vgatherdpd w/o vsib

[mikpe at it dot uu.se]

http://sourceware.org/bugzilla/show_bug.cgi?id=15229

             Bug #: 15229
           Summary: objdump -d allows invalid avx2 vgatherdpd w/o vsib
           Product: binutils
           Version: 2.24 (HEAD)
            Status: NEW
          Severity: normal
          Priority: P2
         Component: binutils
        AssignedTo: address@hidden
        ReportedBy: address@hidden
    Classification: Unclassified


I would expect an AVX2 VSIB-using instruction like VGATHERDPD to be flagged by
objdump as invalid if its ModR/M is of a form that doesn't have a (V)SIB, but
objdump instead disassembles it without complaint:

> cat vsib-test.s 
.text

# this should disassemble as "vgatherdpd %xmm2,(%rax,%xmm7,2),%xmm1"
.byte 0xc4,0xe2,0xe9,0x92,0x0c,0x78

# this should be flagged as invalid
.byte 0xc4,0xe2,0xe9,0x92,0x08
> gas/as-new -o vsib-test.o ../vsib-test.s
> binutils/objdump -d vsib-test.o

vsib-test.o:     file format elf64-x86-64


Disassembly of section .text:

0000000000000000 <.text>:
   0:   c4 e2 e9 92 0c 78       vgatherdpd %xmm2,(%rax,%xmm7,2),%xmm1
   6:   c4 e2 e9 92 08          vgatherdpd %xmm2,(%rax),%xmm1

That last instruction is invalid and will be rejected by gas if you try to
assemble it.

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