MIPS/GAS: Handle --trap command-line option dynamically

We have an ISA check for the '--trap' command-line option that reports
its incompatibility with the MIPS I architecture.  It doesn't prevent
trap instructions from being enabled though, so when attempt is made to
emit one in an expansion of one of the division or multiplication macros
an assertion failure triggers:

.../gas/testsuite/gas/mips/brtr-opt.s: Assembler messages:
.../gas/testsuite/gas/mips/brtr-opt.s:3: Error: trap exception not supported at ISA 1
.../gas/testsuite/gas/mips/brtr-opt.s:9: Warning: divide by zero
.../gas/testsuite/gas/mips/brtr-opt.s:9: Internal error in macro_build at .../gas/config/tc-mips.c:9064.
Please report this bug.

The same assertion failure triggers without an earlier error message
when the initial ISA is compatible with the '--trap', however at the
time an attempt is made to emit a trap instruction from a division or
multiplication macro the ISA has been changed by a '.set' pseudo-op to
an incompatible one.

With the way the situations are mishandled it seems unlikely that anyone
relies on the current semantics and a sane approach is to decide on the
fly according to the currently selected ISA as to whether to emit trap
or breakpoint instructions in the case where '--trap' has been used.

Change our code to do so then and clarify that in the manual, which is
not explicit about how '--trap' is handled with a changing ISA.  Mention
the change in NEWS too since it's a applies to a user option.

0 files changed, 0 insertions, 0 deletions