In reviewing the current state of PR1078, I found that there is no documentation for the H8/3000 function attributes "monitor" and "OS_Task".

The "monitor" attribute is mentioned in invoke.texi, though:

@item -mexr
@opindex mexr
Extended registers are stored on stack before execution of function
with monitor attribute. Default option is @option{-mexr}.
This option is valid only for H8S targets.

@item -mno-exr
@opindex mno-exr
Extended registers are not stored on stack before execution of function 
with monitor attribute. Default option is @option{-mno-exr}. 
This option is valid only for H8S targets.

Besides needing markup fixes and copy-editing, this text is totally confusing:  *both* of these behaviors cannot be the default.  Trying to figure this out from the code, in "monitor_prologue" in h8300.md I see:

...
  else if (TARGET_H8300S && TARGET_NEXR )
    return "mov.l\\ter0,@-er7\;stc\tccr,r0l\;mov.b\tr0l,@(4,er7)\;mov.l\\t@er7+,er0\;orc\t#128,ccr"; 
  else if (TARGET_H8300S && TARGET_NEXR && TARGET_NORMAL_MODE)
    return "subs\\t#2,er7\;mov.l\\ter0,@-er7\;stc\tccr,r0l\;mov.b\tr0l,@(4,er7)\;mov.l\\t@er7+,er0\;orc\t#128,ccr";
...

The second clause is clearly dead code.  I think there is a mistake in logic here, and that a target expert needs to figure out what the intended behavior is and correct both the implementation and documentation.