User guide

3.3. GLOBAL FUNCTIONS 69

directory. If a val i d module is not found ther e and name is a relative ﬁle name, it

searches through the directories speciﬁed by the environment variable whose name

is in the rtn

pathvar element of the rootnode. This name is normally BCPLPATH

under Cintsys and POSPATH under Cintpos. See Section 3.6 for more information about

environment variables.

If l oadi ng is successful, loadseg returns the list of loaded program sections, other-

wise it returns zero. Before the loaded c ode can be used, its gl obal s must be initial i se d

using globin.

Cintcode modules generated by the BCPL compiler are typically text ﬁles con-

taining the compiled code encoded in hexadecimal. The compiled form of the logout

command:

SECTION "logout"

GET "libhdr"

LET start() BE abort(0)

000003E8 0000000E

0000000E 0000FDDF 474F4C0B 2054554F 20202020

0000DFDF 6174730B 20207472 20202020 7B1C2310

00000000 00000001 00000024 0000001C

The ﬁrst two words (000003E8 0000000E) indicate the presence of a “hunk” of code

of size 14(000000E) words whi ch then follow. The ﬁrst word of the hunk (000000E)

is again its length. The next four words (0000FDDF 474F4C0B 2054554F 20202020)

contain the SECTION name "logout". These are followed by the four words 0000DFDF

6174730B 20207472 20202020 which hold the name of the function "start". The

body of start is compiled into one word (7B1C2310) which correspond to the Cintcode

instructions:

L0 Load A wi th 0

K3G 28 Call the func ti on in global 28, incrementing the stack by 3

RTN Return from start – never reached

The remaining 4 words contain global initial i sat i on data that is read backwards during

global initialisation invoked by sys(Sys

globin,...). 0000001C (=28) is the highest

global variable referenced by this section. The pair 00000001 00000024 speciﬁes that

the entry point at position 36 is t he initial value of global 1, and the next entry

(00000000) marks the end of the global i ni ti al i s ati on data.

The manifest constants t hunk, t reloc, t end, t hunk64, t reloc64, t end64,

bhunk, and t bhunk64 are declared in libhdr for the convenience of p r ogram s that

generate or read Cintsys and Cintpos object modules. The example above shows t

hunk

loading n 32-bit words encoded in hex bytes. Although the BCPL compile r used in both

Cintsys and Cintpos generates position independent code and has no need to modify

the loaded words of a hunk, other languages may need to perform relocation. This can

be done using t reloc which is followed by a 32-bit word n encoded in hex followed by a

further n words which each give the position of a word in the most recently loaded hunk