Kenwood HP 9000 manual When to use -h versus +e, $ nm -p sem.o

Linker Tasks

Using Linker commands

$ nm -p sem.o

0000000000 U $global$

1073741824 d $THIS_DATA$

1073741864 b $THIS_BSS$

0000000004 cS sem_val

0000000000 T check_sem_val

0000000036 T foo

0000000000 U printf

0000000088 T bar

0000000140 T sem

In this example, check_sem_val, foo, bar, and sem are all global definitions. To create a shared library where check_sem_val is a hidden, local definition, you could use either of the following commands:

$ ld	-b	-h	check_sem_val	sem.o	One -h option.
$ ld	-b	+e	foo +e bar +e	sem sem.o	Three +e options.

In contrast, suppose you want to export only the check_sem_val symbol. Either of the following commands would work:

$ ld	-b	-h	foo -h bar -h	sem sem.o	Three -h options.
$ ld	-b	+e	check_sem_val	sem.o	One +e option.

When to use -h versus +e

How do you decide whether to use -hor +e? In general, use -hif you simply want to hide a few symbols. And use +e if you want to export a few symbols and hide a large number of symbols.

You should not combine -hand +e options on the same command line. For instance, suppose you specify +e sem. This would export the symbol sem and hide all other symbols. Any additional -hoptions would be unnecessary. If both -hand +e are used on the same symbol, the -hoverrides the +e option.

The linker command line could get quite lengthy and difficult to read if several such options were specified. And in fact, you could exceed the maximum HP-UX command line length if you specify too many options. To get around this, use ld linker option files, described under “Passing Linker Options in a file with -c”. You can specify any number of -hor +e options in this file.

You can use -hor +e options when building a shared library (with -b) and when linking to create an a.out file. When combining .o files with -r, you can still use only the -hoption.

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