For register indirect branches, NOTRACK prefix (0x3e), which is also
the DS segment register prefix, can be used to ignore the CET indirect
branch track.
gas/
* config/tc-i386.c (REX_PREFIX): Changed to 7.
(NOTRACK_PREFIX): New.
(MAX_PREFIXES): Changed to 8.
(_i386_insn): Add notrack_prefix.
(PREFIX_GROUP): Add PREFIX_DS.
(add_prefix): Return PREFIX_DS for DS_PREFIX_OPCODE.
(md_assemble): Check if NOTRACK prefix is supported.
(parse_insn): Set notrack_prefix and issue an error for
other prefixes after NOTRACK prefix.
* testsuite/gas/i386/i386.exp: Run tests for NOTRACK prefix.
* testsuite/gas/i386/notrack-intel.d: New file.
* testsuite/gas/i386/notrack.d: Likewise.
* testsuite/gas/i386/notrack.s: Likewise.
* testsuite/gas/i386/notrackbad.l: Likewise.
* testsuite/gas/i386/notrackbad.s: Likewise.
* testsuite/gas/i386/x86-64-notrack-intel.d: Likewise.
* testsuite/gas/i386/x86-64-notrack.d: Likewise.
* testsuite/gas/i386/x86-64-notrack.s: Likewise.
* testsuite/gas/i386/x86-64-notrackbad.l: Likewise.
* testsuite/gas/i386/x86-64-notrackbad.s: Likewise.