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Annotation of coherent/b/bin/db/Read_me, revision 1.1.1.1

1.1       root        1: db/Read_me 4/2/93
                      2: steve's notes on db source
                      3: 
                      4: A brief history:
                      5: db was originally written ca. 1982 (?) by Johann George for PDP-11 COHERENT.
                      6: It was subsequently ported to i8086, z8001, m68000, etc.
                      7: The source still shows the influence of these versions,
                      8: in particularly the segmentation for PDP-11 and segmented z8001 models.
                      9: It is also complicated considerably by understanding both COFF and l.out.
                     10: 
                     11: The initial i386 version was by a German associate of Frank Pfeifer,
                     12: Bernard Waldt, Waldt Software Consulting, Germany,
                     13: starting from existing i8086 sources.
                     14: He was not an MWC employee, and apparently it never worked.
                     15: hal hacked on the i386 sources somewhat in 1993, cleaning up the
                     16: ptrace() call in the COH386 system and making db sort of work.
                     17: 
                     18: By the time steve got the i386 sources, both machine-independent and
                     19: machine-independent sources lived in the same directory.
                     20: steve restored the subdirectory structure for the benefit of future ports
                     21: and rewrote and reorganized the source considerably; see the Changes
                     22: file for more details.
                     23: 
                     24: In the PDP-11 machine model, the same address could reference i-space (code)
                     25: or d-space (data).  Vestiges of this architecture are still very evident in
                     26: db source (as well as in the ptrace() interface), and make the source
                     27: confusing or wrongheaded for a flat address space machine architecture,
                     28: although much of this code is still necessary to support l.out.
                     29: In particular, a symbol has an associated segment (DSEG or ISEG,
                     30: or USEG for registers), but the mapping of an arbitrary address
                     31: to a segment can be many-one.  This could be clearer in the source.
                     32: 
                     33: Substantial amounts of other source cleanup remain to be done.
                     34: The code often assumes that the host machine object sizes are the same
                     35: as the target machine sizes (4 byte ints); it should instead define its
                     36: own target machine types, like ival_t in the compiler;
                     37: with a little fine-tuning of exec() and ptrace() interface,
                     38: this would allow remote (cross-machine) debugging.
                     39: The machine-independent code used to pass machine addresses in longs,
                     40: now it uses ADDR_T (defined in machine-dependent mdb.h).
                     41: 
                     42: Future coding improvements/ideas:
                     43:        type handling using char_t/short_t/int_t/long_t for target sizes
                     44:        symbol lookup by value: add ordered list field to SYM?

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