Notes
Referring to Professors Niklaus Wirth and Jurg Gutknecht, Project Oberon, The Design of an Operating System, a Compiler, and a Computer, ISBN 0-201-54428-8, Revised Edition 2013.
Fixup
Compilation of a module produces branches in which target addresses are relative to the base of the module. Fixup is the conversion of these addresses to absolute addresses. It is performed by the module loader, Modules.Load, as discussed in section 6.1. Linking and loading, page 79.
In section "6.3. The linking loader" is the paragraph beginning "At the very end of the file three integers called fixorgP, fixorgD, and fixorgT are read."
a) A search for "fixorgP" in the code generator module ORG will find this line in ORG.Call.
Put3(BL, 7, ((-x.r) * 100H + x.a) * 1000H + pc-fixorgP); fixorgP := pc-1
Also, this line is in ORG.Put3.
code[pc] := ((op+12) * 10H + cond) * 1000000H + (off MOD 1000000H); INC(pc)
b) -x.r in an item x for a procedure is the module number, mno, and x.a is the entry number for the procedure, pno.
c) From ORG.Call and ORG.Put3 deduce,
the 4 bits [20..23] = -x.r (= the module number, mno) the 8 bits [12..19] = x.a (= the entry number for the procedure, pno) the 12 bits [0..11] = pc-fixorgP (= the displacement between 2 instructions in the fixup chain)
With steps (a-c) the compiler generates this instruction precursor.
| BL (4) | cond (4) | mno (4) | pno (8) | pc-fixorgP (12) |
The precursor is not formatted as an instruction but is the same length as one, 32 bits.
d) The lines of (c) correspond to these lines in Modules.Load.
mno := inst DIV 100000H MOD 10H; pno := inst DIV 1000H MOD 100H; disp := inst MOD 1000H;
Modules.Load converts the precursor to the second (u=1) F3 format of RISC-Arch.pdf section 3.
| BL (4) | cond (4) | offset relative to PC (24) |
Refer to ORG.Call and Modules.Load and to the mailing list at 2019-11-18 and at 2020-12-16..18.
Text in Oberon V5
Type | Fields of TextDesc | Types of Fields | Notes |
---|---|---|---|
Texts.Text, a pointer to a Texts.TextDesc | len | INTEGER[1] | Length of text, in bytes. |
changed | BOOLEAN | Flag indicating a revision. | |
notify | Texts.Notifier | Pointer to a method to notify interested clients of state changes. | |
trailer | Texts.Piece | Pointer to the Sentinel node in the list of pieces. | |
pce | Texts.Piece | Last found piece. | |
org | INTEGER | Offset in [0,len) of first character in last found piece. |
Type | Fields of PieceDesc | Types of Fields | Notes |
---|---|---|---|
Texts.Piece, a pointer to a Texts.PieceDesc | f | Files.File | Pointer, to file. |
off | INTEGER | Integer offset in Text of first character in Piece. | |
len | INTEGER | Number of bytes in Piece. | |
fnt | Fonts.Font | Pointer to a font. | |
col | INTEGER | ||
voff | INTEGER | Vertical offset of characters in pixels. | |
prev | Texts.Piece | Pointer to previous piece of Text. | |
next | Texts.Piece | Pointer to next piece of Text. |
Sources in Oberon V5
Published V5 | Variant | Notes |
---|---|---|
Files.Mod | ||
Out.Mod | Allow delay of execution of Append, using a flag variable. | |
Out1.Mod | Allow delay of execution of Append, using a procedure variable. | |
Texts.Mod |
- ↑ In V5 the only integer type is INTEGER. Cf. LONGINT in V2.