PATCH: Re: 971225: bootstrap fails on powerpc-unknown-linux-gnu*

[Jeffrey A Law]

  In message <v03130302b0f6b969485c@[195.180.235.165]>you write:
  > Hi,
  > 
  > the reported bootstrap fail on Linux/PPC was introduced in rev. 1.3 of
  > rs6000/sysv4.h by a #undef JUMP_TABLES_IN_TEXT_SECTION. linux.h includes
  > sysv4.h but didn't override the change.
  > Eventually this hides a bug in binutils?
  > 
  > Bye,
  > Franz.
  > 
  > 
  > Tue Jan 29 22:44:00 1998 Franz Sirl <franz.sirl-kernel@lauterbach.com>
  > 	* rs6000/linux.h: define JUMP_TABLES_IN_TEXT_SECTION
Thanks.  I installed this patch.

As Geoffrey noted, the real problem is how we handle switch tables
in general.  I ran into the same group of problems when trying to
change the PA port from using an indexed jump into jumps to case
labels.  We had something like this:

start of tablejump insn
	blr
	nop
start of ADDR_VEC insn
	jmp case1
	nop
	jmp case2
	nop
	jmp case3



What I wanted to do was a more traditional scheme where either offsets 
or actual locations are kept as a table (it's the first step towards
a much more branch prediction friendly tablejump on the PA).

On the PA it is absolutely necessary to never mix data into a code
section.  So these tables needed to go into readonly data...  And
bang I ran into the same problems y'all are running into.

I banged my head on the wall for about an hour or so trying to find
an easy solution and just gave up when I realized that some fundamental
changes in our switch/tablejump code would be necessary to make it
work.

jeff