Conference tallis::alpha_migration_tools

963.0. "Data mapping problems Vax C vs. Alpha C" by JAMSIE::CORBETT () Tue Apr 08 1997 05:38

I have a problem with porting code from VAX to ALPHA.
This particular problem occurs with mapping data to data structures.

The code reads VMS error log files and interprets the header. It works 
correctly on VAX but then loses data (on alignment) on the ALPHA.

The essential pieces of code and data are seen below :
1. the struct definition;
2. the mapping to memory 'vms_hdr';
3. the mapping from read buffer to memory;
4. a dump of the first file block.

The two columns alongside the struct definition show the hex values
assigned to the data items in the struct after memory mapping (the data
in the buffer is correct on both machines according to the dump). The 
error occurs consistently with other files.

The mis-alignment seems to start following the 'short rev' item 
where the two bytes 0101 are lost from the ALPHA data
(another mis-alignment occurs later following another 'short').

1.
typedef struct hdr_ptype {		VAX		ALPHA
        int     sid;			0B000006	0B000006
        short   rev;			FFFB		FFFB
        int     systype;		02300101	00040230
		.
        } vms_hdr_stype;
		.
2.		.
vms_hdr_stype                   vms_hdr;
		.
3.		.
while ((file_status = ReadFile(in_file_ptr->filename)) != RMS$_EOF)
{
if (file_status == FILEERROR) break;

temp_hdr_ptr = (vms_hdr_stype *) buffer;
vms_hdr = *temp_hdr_ptr;

4.
Dump of file DPP$USER:[CORBETT.LOCALMPH.DATA]ERRLOG.OLD;53 on  8-APR-1997 07:48:07.58
File ID (29598,113,0)   End of file block 87 / Allocated 87

Virtual block number 1 (00000001), 512 (0200) bytes

 00000000 00202020 4F535050 44080000 00000004 02300101 FFFB0B00 00060040 @.....�...0........DPPSO   ..... 000000
 C0060000 00002020 2020312E 36560000 009A8FD7 76E97F28 00234001 00000000 .....@#.(.�v�.....V6.1    .....� 000020
 00000020 20204F53 50504408 00000000 00040230 0101FFFB 0B000006 00400029 ).@.....�...0........DPPSO   ... 000040
				.
 20202020 312E3656 143F009A 912FC95C 38280041 40010000 00000000 00000020  ..........@A.(8\�/...?.V6.1     0001E0



When I compile cc/SHOW=ALl on the VAX I get a listing of the data dictionary.

When I compile with the same parameters on the ALPHA, there is no dictionary listing
although the help command states that the data dictionary listing should appear.

Can anyone help with explanations and suggestions, please??

Daniel

This is most likly a question for the TURRIS::DECC conference.

Have you tried #pragma directives or /member_align

VAXC did not pad structions, DECC does.

bjm