Proposal : Implement SEH exceptions into [ce]gcc

[mosfet <forumer at smartmobili dot com>]

Hi,

I am working on mobile CE devices and I use cegcc (when it's possible) to
developp software.
There is one feature I miss with gcc called SEH exceptions and since I have
seen a recent post 
about SEH x64 I think it's the right moment to talk about it.

First SEH exceptions exists in two kinds :

1) SEH called "frame-based" and I think that historically it was the first
kind of implementation. This 
is described here
http://www.microsoft.com/msj/0197/exception/exception.aspx.
I think this mechanism is used only on x86(32 bits) because it relies on a
specific register FS:[0] and is based on a linked list.

2) SEH called "table-based" used on all other platforms(x64, ARM, MIPS,
...) than x86.
In this case exception info are stored into a .pdata section (at least on
ARM not sure about x64)

The Function Table (interpreted .pdata section contents)
 vma:		Begin    Prolog   Function Flags    Exception EH
     		Address  Length   Length   32b exc  Handler   Data
 00014000	00011008 00000004 00000015  1   1   00011090  000120dc
 00014008	0001105c 00000001 00000009  1   0   e24bd010  e89da810
 00014010	000110a0 00000002 00000093  1   0   e12fff1c  00013004
 00014018	000112f4 00000004 00000030  1   1   00011090  000120f0
 00014020	000113b4 00000001 0000000b  1   0   e91b6810  e12fff1e
 00014028	000113e0 00000001 0000001b  1   0   0001305c  00013058
 00014030	0001144c 00000001 00000041  1   0   00013040  0001303c
 00014038	00011550 00000001 00000006  1   0   00013070  00013074
 00014040	0001157c 00000002 0000000e  1   0   01b0c820  012fff1e
 00014048	000115c0 00000001 00000014  1   0   00013054  0000b064


 typedef struct _SCOPE_TABLE {
     ULONG Count;
     struct
     {
         ULONG BeginAddress;
         ULONG EndAddress;
         ULONG HandlerAddress;
         ULONG JumpTarget;
     } ScopeRecord[1];
 } SCOPE_TABLE, *PSCOPE_TABLE;

SEH and gcc seems to be a long story because someone called Casper
Hornstrup already had implemented 
frame-based SEH in 2003 for gcc 3.2 but his patch was never accepted for
some bad reasons(it's a MS thing, Borland patents, ...).

So I have proposed an internship to one student and he will try to
implement table-based SEH exceptions into cegcc.
He will work on it for six months, three days a week so I hope he will find
some help on this ML.
Normally this work will also benefit to x64 because the mechanism is almost
the same.

If you have suggestions/remarks/advice or if you want to participate please
let us know. 

Some resources :
[Frame Based SEH]
http://www.microsoft.com/msj/0197/exception/exception.aspx

[Table Based SEH on X64 - available only through Google cache]
http://209.85.129.132/search?q=cache:ycabCQnoeFoJ:www.osronline.com/article.cfm%3Farticle%3D469+SEh+x64&hl=fr&ct=clnk&cd=1&gl=fr

[Table Based SEH on ARM]
http://code-factor.blogspot.com/2007/04/windows-ce-seh-for-arm-with-gcc.html

[Misc]
http://code-factor.blogspot.com/2007/09/windows-seh-revisited.html
http://blogs.msdn.com/jaredpar/archive/2008/01/11/mixing-seh-and-c-exceptions.aspx
http://cygwin.com/ml/cygwin/2002-08/msg01598.html


Vincent Richomme
http://www.smartmobili.com