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Re: relaxation segv
- To: Richard Henderson <rth at redhat dot com>
- Subject: Re: relaxation segv
- From: Alan Modra <alan at linuxcare dot com dot au>
- Date: Sun, 11 Mar 2001 23:14:28 +1100 (EST)
- cc: binutils at sources dot redhat dot com
On Sun, 11 Mar 2001, Richard Henderson wrote:
> If a relaxation expresion involves differences between symbols
> in a different section, then we need to relax the sections in
> the proper order. Moreover, there can be loops in the dependancy
> graph that require us to re-run relaxation on a section.
It's worse than that, actually. Try this little gem involving only
symbols in one section:
.org (Z2 - Z0 + 4) + .
.space 0x7e, 0x90
orgbug2.o: file format elf32-i386
Disassembly of section .text:
0: 0f 84 7e 00 00 00 je 84 <Z9>
2: 7e 00 jle 4 <Z2+0x2>
6: 90 nop
7: 90 nop
Note the "interesting" values of Z1 and Z2. Changing the `+ 4' and
`0x7e' to other values results in various other "interesting" behaviour.
I believe all of these problems are due to a fundamentally broken method
of symbol resolution where expressions are involved. One thought I had
about this a long time ago, and never followed up, is to not set
sy_resolved on expression symbols during relaxation. More importantly,
don't set sy_resolved on the components of an expression as it's really
premature setting of sy_resolved that's causing your testcase failure.