eld Manual

eld Input and Output
eld Manual—527255-009
2-7
Creating Segments of the Output Loadfile
and what additional rules should be enforced, as shown in the following table. eld
reports an error if you specify the -instance_data option more than once with
different parameters. eld reports an error if you specify -instance_data with -r.
* The data2protected parameter is supported only on systems running J06.09 or earlier J-series RVUs and H06.20
or earlier H-series RVUs.
If the loadfile being created had no data that would go into the data variable segment
then the linker sets the data1constant bit in the e_flags field of the ELF file header.
Otherwise, the linker sets the bit that corresponds to which parameter was given to the
-instance_data option. The three different values set in the e_flags field in these
cases tell the HP NonStop operating system how to protect the data variable segment.
When the -make_implicit_lib option is used, -instance_data
data1constant is imposed, and eld reports an error if you specify
-instance_data with any other parameter value.
There is no special boundary between the initialized data and the uninitialized data in
the data (variable) segment. If the last portion of initialized data happens to be zero,
the linker considers it to be within the uninitialized data, because what is called
“uninitialized” data gets initialized to zero by the operating system. That possibly
makes the size of the initialized data smaller within the object file. Based on this, the
linker will fill in the p_filesz field of the appropriate program header. On the other hand,
the linker also rounds up this value to a multiple of 4 kilobytes, thus possibly making
the size of the initialized data larger. This tells the amount of space occupied by the
appropriate segment within the loadfile, and the portion rounded up by the linker is
initialized to zero in the loadfile.
The program header of type PT_TANDEM_RESIDENT points at the .restext section,
that is, the resident code. There is no special boundary between the resident and non-
resident code.
For a DLL the -t option specifies the starting address of the text segment of the DLL
in memory. If the -t option is not used then it is possible for the DLLs address to be
determined by using a DLL registry, as covered in the sub-section below.
Table 2-1. Parameters to the -instance_data Option
Parameter Meaning
data1 Create one data segment. (This is the
default.)
data2
data2protected*
data2hidden
These three cases tell the linker to create
two data segments, i.e., the “data
constant” segment and the “data variable”
segment.
data1constant It is an error to have any data that would
need to go into the data variable segment
if we were told to create two segments.