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Avoid a build error with microMIPS compilation and recent versions of GAS which complain if a branch targets a label which is marked as data rather than microMIPS code: ../sysdeps/mips/mips32/crti.S: Assembler messages: ../sysdeps/mips/mips32/crti.S:72: Error: branch to a symbol in another ISA mode make[2]: *** [.../csu/crti.o] Error 1 as commit 9d862524f6ae ("MIPS: Verify the ISA mode and alignment of branch and jump targets") closed a hole in branch processing, making relocation calculation respect the ISA mode of the symbol referred. This allowed diagnosing the situation where an attempt is made to pass control from code assembled for one ISA mode to code assembled for a different ISA mode and either relaxing the branch to a cross-mode jump or if that is not possible, then reporting this as an error rather than letting such code build and then fail unpredictably at the run time. This however requires the correct annotation of branch targets as code, because the ISA mode is not relevant for data symbols and is therefore not recorded for them. The `.insn' pseudo-op is used for this purpose and has been supported by GAS since: Wed Feb 12 14:36:29 1997 Ian Lance Taylor <ian@cygnus.com> * config/tc-mips.c (mips_pseudo_table): Add "insn". (s_insn): New static function. * doc/c-mips.texi: Document .insn. so there has been no reason to avoid it where required. More recently this pseudo-op has been documented, by the microMIPS architecture specification[1][2], as required for the correct interpretation of any code label which is not followed by an actual instruction in an assembly source. Use it in our crti.S files then, to mark that the trailing label there with no instructions following is indeed not a code bug and the branch is legitimate. References: [1] "MIPS Architecture for Programmers, Volume II-B: The microMIPS32 Instruction Set", MIPS Technologies, Inc., Document Number: MD00582, Revision 5.04, January 15, 2014, Section 7.1 "Assembly-Level Compatibility", p. 533 [2] "MIPS Architecture for Programmers, Volume II-B: The microMIPS64 Instruction Set", MIPS Technologies, Inc., Document Number: MD00594, Revision 5.04, January 15, 2014, Section 8.1 "Assembly-Level Compatibility", p. 623 2016-11-18 Matthew Fortune <Matthew.Fortune@imgtec.com> Maciej W. Rozycki <macro@imgtec.com> * sysdeps/mips/mips32/crti.S (_init): Add `.insn' pseudo-op at `.Lno_weak_fn' label. * sysdeps/mips/mips64/n32/crti.S (_init): Likewise. * sysdeps/mips/mips64/n64/crti.S (_init): Likewise. |
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