MIPS64R6 jalr[.hb] $zero, $ra should be treated as a return variant #7355
Description
As per MIPS® Architecture For Programmers Volume II-A: The MIPS64® Instruction Set Reference Manual, Revision 6.06, pp. 272:
Release 6 maps JR and JR.HB to JALR and JALR.HB with rd = 0:
Pre-Release 6, JR and JALR were distinct instructions, both with primary opcode SPECIAL, but with distinct function codes.
Release 6: JR is defined to be JALR with the destination register specifier rd set to 0. The primary opcode and function field are the same for JR and JALR. The pre-Release 6 instruction encoding for JR is removed in Release 6.
Release 6 assemblers should accept the JR and JR.HB mnemonics, mapping them to the Release 6 instruction encodings.
jalr[.hb] $zero, $ra is architecturally synonymous with jr[.hb] $ra, and both should be treated as return instructions. However, the current lifter fails to do so:
binaryninja-api/arch/mips/arch_mips.cpp
Lines 336 to 339 in 9e83ea1
binaryninja-api/arch/mips/arch_mips.cpp
Lines 383 to 390 in 9e83ea1