I wanted to extract information about DSECTS from the SYSADATA output from compiling an assembler program on z/OS.

On the whole it was pretty easy – but had some surprises!

I’ve put some Python code up on github. It runs on my z/OS.

Where is the record layout documented?

The record layout is documented in HLASM V1R6 Programmer’s Guide. Dsects for the various types are provided in HLA.SASMMAC1(ASMADATA).

I used record type 0x0042 for symbols. To get a record in this section of the ADATA it needs a label.

For example

      DSECT COLIN2
ABCD  DS CL8
ABCDE DS CL8

This will not produce a record for the DSECT – because it does not have a label.

ESDID – section names

Each DSECT or CSECT will have an External Symbol Directory ID.

• CSECT start at 1, and increment, so 1,2
• DSECTs start at -1 and decrement 4294967295= 0xffffffff(-1), 4294967294 = 0xfffffffe(-2)

Field order

The order of records seems to be random. The CSECT/DSECT statement is often after some fields in the CSECT/DSECT.

To find the xSECT for each symbol, I saved the SECT name and ESDID, and post processed the list of symbols by adding the xSECT information afterwards from the ESDID.

Field offsets

The offsets in each record seem to be the offset from the first instruction. I had to save the offset from the CSECT statement, then post process the records to calculate (offset of symbol in CSECT) = symbol offset – start_of_CSECT offset.

“Problems”

Missing data

To get a record into the ADATA ensure it has a label.

Output from my code

     ESDID              Symbol  Offset  Length TypeA       SymType    CSECT
4294967295                ABCD       0       8     C OrdinaryLabel   COLIN2
4294967295              COLIN2       0       1     J         DSECT   COLIN2
4294967295               ABCDE       8       8     C OrdinaryLabel   COLIN2
         1            CSQ6LOGP       0       1     J         CSECT CSQ6LOGP
         1                LOGP       0       8     D OrdinaryLabel CSQ6LOGP
         1              LOGPID       0       2     R OrdinaryLabel CSQ6LOGP
         1              LOGPLL       2       2     R OrdinaryLabel CSQ6LOGP
         1             LOGPEID       4       4     C OrdinaryLabel CSQ6LOGP
         1            LOGPMRTU       8       2     R OrdinaryLabel CSQ6LOGP
         1             LOGOPT1      10       1     R OrdinaryLabel CSQ6LOGP
         1             LOGOPT2      11       1     R OrdinaryLabel CSQ6LOGP
         1            LOGPMCOF      12       2     R OrdinaryLabel CSQ6LOGP
         1            LOGPOBPS      16       4     R OrdinaryLabel CSQ6LOGP
         1            LOGPIBPS      20       4     R OrdinaryLabel CSQ6LOGP
         1            LOGPARCL      24       4     R OrdinaryLabel CSQ6LOGP
         1            LOGPWRTH      30       2     R OrdinaryLabel CSQ6LOGP
         1             LOGPLVL      32       7     C OrdinaryLabel CSQ6LOGP
         1            LOGPLVLN      39       1     R OrdinaryLabel CSQ6LOGP
         1            LOGPDMIN      40       2     R OrdinaryLabel CSQ6LOGP
         1            LOGPDSEC      42       2     R OrdinaryLabel CSQ6LOGP
         1            LOGPCOMP      44       4     R OrdinaryLabel CSQ6LOGP
         1             LOGPEND     256       1     U           EQU CSQ6LOGP