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pfcom.htm
Procedures
PfcomCompile
PfcomLoadPgm

This source PF generates EuroAssembler output object file in program format COM.

pfcom PROGRAM FORMAT=COFF,MODEL=FLAT,WIDTH=32
INCLUDEHEAD "euroasm.htm" ; Interface (structures, symbols and macros) of other modules.
INCLUDEHEAD  \  ; Include headers of another modules used in this module.
ea.htm,      \
eaopt.htm,   \
exp.htm,     \
msg.htm,     \
pf.htm,      \
pfpe.htm,    \
pgm.htm,     \
pgmopt.htm,  \
reloc.htm,   \
sss.htm,     \
stm.htm,     \
sym.htm,     \
syswin.htm,  \
;;

 pfcom HEAD ; Start module interface.

 ENDHEAD pfcom  ; End of module interface.

↑ PfcomCompile OutputStream, Pgm

PfcomCompile is constructor of output 16bit real-mode executable file image in COM format.
This format by default uses one common segment [COM]. Entry point is fixed at [COM]:100h.
Emitted contents of segment(s) is stored to output stream without any metainformations,
it starts at the entry point, which is the first byte in the output file.

Load-time relocations are not possible, the loader fills CS,DS,ES,SS with paragraph addres of [COM],
so DS:0 points to 256 bytes long Program Segment Prefix (PSP).

Segment are typically not used in COM format. If more than one segment is used in the program,
segments are linked to output image file with alignment specified by the strongest of following three options:

• PROGRAM FILEALIGN= (default=0),
• PROGRAM SECTIONALIGN= (default=0),
• SEGMENT ALIGN= (default=16).

Segment order has been set up by PgmOrderSegments.
Relative relocations between segments are resolved. Absolute relocations are fixed up as if the image (starting with PSP) was loaded at virtual address VA=0. The program has to manage such relocations by itself at run time.

Input

OutputStream is pointer to a STREAM for the output image contents.
Pgm is pointer to PGM representing completely assembled program.

Output

OutputStream is filled with output file contents.

Error

Errors are reported with macro Msg.

Invoked from

PfOutput

Invokes

EaBufferRelease EaBufferReserve PgmEvalEntry PgmGroupByModel PgmLink PgmOrderSegments PgmRelocResolve PgmStreamImage RelocReportUnresolved SssFindByPurpose SymReportUnresolved

Tested by

t8250 t8362 t8750 t8762

PfcomCompile Procedure OutputStream, Pgm
     MOV EBX,[%Pgm]
     Invoke SymReportUnresolved::,EBX
     Invoke PgmGroupByModel::,EBX
     Invoke PgmOrderSegments::,EBX
     SUB EAX,EAX
     CMP [EBX+PGM.Pgmopt.ImageBaseLow],EAX
     Msg cc=NZ,'3932',[EBX+PGM.Pgmopt.ImageBaseLow]  ;  Format COM requires "PROGRAM ImageBase=0". The value !1K ignored.
     MOV [EBX+PGM.Pgmopt.ImageBaseLow],EAX
     MOV [EBX+PGM.Pgmopt.ImageBaseHigh],EAX
     Invoke PgmLink::,EBX,0,100h
     ; Check program entry.
     Invoke PgmEvalEntry::,EBX
     LEA EDX,[EBX+PGM.EntryExp]
     MOV ECX,[EDX+EXP.Status]
     LEA EAX,[EBX+PGM.Pgmopt.EntryPtr]              ; ENTRY= value in case of W3931.
     Dispatch CL,'A','N',00
     JMP .W3931:                                    ; Format COM requires fixed entry point at [!1S]:100h. "ENTRY=!2S" ignored.
.A:  BufferRetrieve [EBX+PGM.SegOrdBuffer]
     LODSD
     CMP EAX,[EDX+EXP.Seg]
     JNE .W3931:
.N:  CMPD [EDX+EXP.Low],100h
     JE .00:
.W3931:
     Invoke EaBufferReserve::,%^PROC
     MOV EDX,EAX
     Invoke SssFindByPurpose::,sssGroup,sssPurposeCODE,sssNotBSS,0,EBX,EDX
     XOR EAX,EAX
     BufferRetrieve EDX
     JZ .70:
     LODSD
.70: Invoke EaBufferRelease::,EDX
     LEA ECX,[EBX+PGM.Pgmopt.EntryPtr]
     Msg '3931',EAX,ECX                               ; 3931 Format COM requires fixed entry point at [!1S]:100h. "ENTRY=!2S" ignored.
.00: Invoke PgmRelocResolve::,EBX
     Invoke RelocReportUnresolved::,EBX
     Invoke PgmStreamImage::,EBX,[%OutputStream]
    EndProcedure PfcomCompile

↑ PfcomLoadPgm BasePgm, ObjBegin, ObjEnd, FileNamePtr

Executable format COM is not linkable, it cannot be loaded.

Input

BasePgm is pointer to an existing PGM to which the object file is being linked/imported.
ObjBegin is pointer to the contents of linked/imported object file mapped in memory by the caller.
ObjSize is number of bytes in the object file.
FileNamePtr is pointer to zero-terminated object file name (used in error reports).

Output

-

Error

E8534 Format !1S of file "!2$" is not linkable.

Invoked from

PfLoad

PfcomLoadPgm Procedure BasePgm, ObjBegin, ObjSize, FileNamePtr
    Msg '8534',Dict_FormatCOM::,[%FileNamePtr] ; Format !1S of file "!2$" is not linkable.
   EndProcedure PfcomLoadPgm

  ENDPROGRAM pfcom