<html>
    <head>
      <base href="https://bugs.llvm.org/">
    </head>
    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW - After r315899, .byte directives after x86 prefixes cause errors"
   href="https://bugs.llvm.org/show_bug.cgi?id=35749">35749</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>After r315899, .byte directives after x86 prefixes cause errors
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>new-bugs
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>trunk
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>PC
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>All
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>release blocker
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>new bugs
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>unassignedbugs@nondot.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>dimitry@andric.com
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>llvm-bugs@lists.llvm.org
          </td>
        </tr></table>
      <p>
        <div>
        <pre>Related to <a class="bz_bug_link 
          bz_status_ASSIGNED "
   title="ASSIGNED - After r315899, comments after x86 prefixes cause errors"
   href="show_bug.cgi?id=35741">bug 35741</a>, after <a href="https://reviews.llvm.org/rL315899">https://reviews.llvm.org/rL315899</a> (fixing x86
prefix issues related to <a class="bz_bug_link 
          bz_status_RESOLVED  bz_closed"
   title="RESOLVED FIXED - [MC] Disassembler does not support x86 instruction prefixes"
   href="show_bug.cgi?id=7709">bug 7709</a>, <a class="bz_bug_link 
          bz_status_RESOLVED  bz_closed"
   title="RESOLVED FIXED - [x86 disassembler] Wrong disassemble for some SSE2 instructions."
   href="show_bug.cgi?id=17697">bug 17697</a>, <a class="bz_bug_link 
          bz_status_RESOLVED  bz_closed"
   title="RESOLVED FIXED - [x86 disassembler] prefix ordering may ignore opsize and rep[n]e prefixes"
   href="show_bug.cgi?id=19251">bug 19251</a>, <a class="bz_bug_link 
          bz_status_RESOLVED  bz_closed"
   title="RESOLVED FIXED - [x86 disassembler] 'xchg' instruction uses two different sized register operands with data16 prefix"
   href="show_bug.cgi?id=32809">bug 32809</a> and bug
21640), .byte directives directly after an x86 instruction prefix are no longer
accepted.

For example:

rep
.byte 0xa4      # movsb

This is accepted by both clang before r315899 and GNU as, but clang r315899
gives:

rep-byte.s:1:1: error: invalid instruction mnemonic '.byte'
rep
^~~

Note that this construct is used to put rep prefixes on instructions that might
not be known by the assembler yet, such as VIA C3 "xcrypt-cbc" instructions
[1]:

        /* The .byte line is really VIA C3 "xcrypt-cbc" instruction */
        __asm __volatile(
                "pushf                          \n\t"
                "popf                           \n\t"
                "rep                            \n\t"
                ".byte  0x0f, 0xa7, 0xd0"
                        : "+a" (iv), "+c" (count), "+D" (out), "+S" (in)
                        : "b" (key), "d" (cw)
                        : "cc", "memory"
);

[1]
<a href="https://github.com/freebsd/freebsd/blob/master/sys/crypto/via/padlock_cipher.c#L92">https://github.com/freebsd/freebsd/blob/master/sys/crypto/via/padlock_cipher.c#L92</a></pre>
        </div>
      </p>


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