Re: gcc-4.1.2 miscompiles setedit from CVS

[Baurzhan I. <ib...@at...>]

On Wed, Aug 23, 2006 at 01:36:50PM -0300, Salvador Eduardo Tropea wrote:
> >The second error is related to packed attribute in setedit/runprog.cc:
> >
> >g++  -I../include -I../setedit/include -I../settvuti/include
> >-I../sdg/include -I../infview/include -I../../tvision/include -I../extra
> >-I../easydiag -I../librhuti -I../mp3 -I../calcu -I../holidays
> >-DFOR_EDITOR -O2 -pipe  -c ../setedit/runprog.cc -o obj/runprog.o
> >../setedit/runprog.cc: In function 'void ConfigureRunCommand()':
> >../setedit/runprog.cc:95: warning: 'packed' attribute ignored for field
> >of type 'char [256]'
> >../setedit/runprog.cc:99: warning: 'packed' attribute ignored for field
> >of type 'char [4]'
> >../setedit/runprog.cc:116: error: cannot bind packed field
> >'box.ConfigureRunCommand()::<anonymous
> >struct>::tl.TListBoxRec::selection' to 'ccIndex&'
> 
> I don't understand it. Sure that char[4] is already 32 bits aligned but 
> I don't want to assume that it means that this is also "aligned" for 64 
> and 128 bits machines. So that's a silly warning.

The warning is not silly, it says that the compiler ignores the
attribute. __attribute__((packed)) packs the field itself (which in case
of char[] is already packed), it doesn't have any impact on the
surrounding fields. You probably want the following (untested):

diff -Naurp setedit.orig/setedit/runprog.cc setedit/setedit/runprog.cc
--- setedit.orig/setedit/runprog.cc	2004-08-11 19:34:06.000000000 +0200
+++ setedit/setedit/runprog.cc	2006-08-23 21:28:19.000000000 +0200
@@ -92,13 +92,13 @@ void ConfigureRunCommand(void)
  #pragma pack(1)
  struct
  {
-  char   ComAux[maxCommand]  __attribute__((packed));
-  uint32 Options             __attribute__((packed));
-  uint32 OpsScroll           __attribute__((packed));
-  uint32 OpsScrHz            __attribute__((packed));
-  char   Lines[4]            __attribute__((packed));
-  TListBoxRec tl             __attribute__((packed));
- } box;
+  char   ComAux[maxCommand];
+  uint32 Options;
+  uint32 OpsScroll;
+  uint32 OpsScrHz;
+  char   Lines[4];
+  TListBoxRec tl;
+ } __attribute__((packed)) box;
  #pragma pack()
  strcpy(box.ComAux,Command);
  box.Options=Options & (~edsmScrollMask);


> Is the error related to the warning? what happends if you remove the
> packed attribute to the above mentioned members?

I'd like to hear an explanation if you find it. At first I thought that
box.ConfigureRunCommand()::<anonymous struct>::tl.TListBoxRec::selection
is packed, and ccIndex is not, thus the error. However, this doesn't
explain why the problem goes away with the fix from Witek.


With kind regards,
Baurzhan.