On Tue, 17 Aug 2021, Ralf Baechle wrote:

quoted

While I was testing v5.4.142-rc2 I noticed mips build of
decstation_r4k_defconfig fails with binutils-2_37. The error is:

arch/mips/dec/prom/locore.S: Assembler messages:
arch/mips/dec/prom/locore.S:29: Error: opcode not supported on this
processor: r4600 (mips3) `rfe'

I have also reported this at https://sourceware.org/bugzilla/show_bug.cgi?id=28241

It would appear gas got more anal about ISA checking for the RFE instructions
which did only exist in MIPS I and II; MIPS III and later use ERET for
returning from an exception.

 Yes, I made such a change when I discovered the mess around coprocessor 
instructions in binutils earlier this year.  Eighteen patches total to 
straighten it out.  Some instructions were misassembled even, and no 
proper subsetting was made, so you could come with a nonsensical mixture 
when disassembling.  And RFE was disassembled as `c0 0x10' regardless of 
the ISA chosen.

It should be fixable by simply putting gas into mips1 mode.  Can you test
below patch?

 But it's missing the point, as I noted in the other message.  I've been 
too busy with higher priority stuff to get to a proper fix right away (I 
thought I was the last one using the DECstation, and especially with the 
top of the tree binutils).

  Maciej