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The BALGOL Library routine ERROR is called by other routines in the Library to report error messages (see Appendix F in the BAC manual, INPUT-OUTPUT PROCEDURES). Portions of ERROR are also used by the LABEL and TRACE routines. ERROR has an 11-word buffer labeled OUT at relative offset 0037 where the message is constructed. It then outputs the message with a call to the RITE routine at offset 0034:

      F4246 1106,44,0100
      F4246 OUT,30,0100

This is a typical STP(44)-BUN(30) call, but with parameter information in the /44 control fields of both instructions: 1106 in the STP control field specifies message length and formatting; OUT in the BUN control field specifies the message buffer address. The sign-6 on both instructions causes the /04 address field to be relative to the start of an external identifier, in this case 01=RITE + 00.

The problem here is that the address of OUT in the /44 control field needs to be relocated as well, but this is not specified. Thus, RITE outputs from absolute address 0037, not the buffer at OUT, resulting in garbage.

The control field would normally be relocated by specifying a sign of 7 on the word, but the sign already has a value of 6 to relocate the /04 address field. Note that the address of OUT is properly relocated by the sign of 8 in the OUT1 word at offset 0053.

This appears to be an original bug, at least in the listing we have available. It can probably be fixed by preceding the BUN instruction word at offset 0035 by a pseudo-operation word with a sign of 4 and an operation code of 04 (, i.e., 4 0000 04 0000). See Appendix F, RELOCATION CONVENTIONS.