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<== Date ==> <== Thread ==>

Subject: RE: Cross compiler source and patch file for gcc-2.7.2 on Linux
From: dht <dht@ornl.gov>
To: "David H. Thompson" <thompsondh@ornl.gov>, Brian McAllister <brian@hotrats.mit.edu>
Cc: techtalk <tech-talk@aps.anl.gov>
Date: Mon, 15 Jul 2002 13:50:37 -0400
I have been building and using gcc to compile c++ on versions of vxWorks all 
the way back to `92 or so, so I have been through several versions and 
changes.  Most versions of gcc support vxWorks OK as long as all of the code 
is compiled with the same compiler. One commercial product that I have used in 
the past, RTI Control Shell, shipped a compiler with their product for many 
years. At some point, at 2.6 or 2.7 the name mangling changes slowed down and 
details of the binary interface became more important.   I am talking aout 
things like how variables are pushed on the stack, register usage, variable 
alignment in structs and classes, lots of stuff under the hood that ld would 
not know about.

What we ran into with Epics 3.14 and not 3.13 was not the use of c++ in Epics 
but the introduction of heavy use of c++ exceptions.   The various versions of 
gcc went from one set of functions in the hidden binary interface to another 
and back.  I had a slide at the San Jose Epics meeting last December that 
showed how the exception API changed from version to version.  But it is more 
complicated than that. Since is vxWorks a multi-thread RTOS, the exception 
handler have to be re-entrant and the ones in the gnu libc.a are not.  This 
matters because an exception might not always be some kind of fatal error but 
in fact one way to write a program's normal execution flow. In that case, 
destructors must run and each stack frame cleaned up back up to the 'catch'. 
The exception handlers that are used by the the 2.7.2 WRS compiler are in the 
5.4 kernel. I don't know if 5.3 included them or not. To change the compiler 
you would have to change the exception handlers in the kernel. We, at SNS, did 
not want to buy the kernel code or write our own version from scratch.  If you 
have doubts about about this choice, just imagine writing code to implement an 
undocumented API and then testing it.

In the end, the conclusion that we came to was that the best way was to pursue 
the compiler source under GPL with Wind River.  That turned out to be easy 
once the right contact at WRS was found.  The changes that I made were just to 
port the compiler to Linux using an up to date compiler to build it.



>I built gcc-2.7.2.3 from the standard source distribution (not WRS), with
>this configuration:
....
>
>I have been using this on Redhat 7.0 to build EPICS 3.13.[1,2,4] for mv167
>and mv177 targets loading vxWorks V5.3 kernels built with the official
>Tornado 1.0 tools on Solaris.  I have had no problems.
>
>I tried gcc-2.8.1 first, which produced code which would load, but not
>execute.
>
.....
>I have not tried this with other target architectures, and the only C++
>code built is what's in 3.13 base.
>
>Did you try the standard gcc-2.7.2.3 ?
>
>Did WRS make further changes which are needed for PPC, EPICS 3.14 or
>vxWorks 5.4 ?


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