GDB: Add a character string limiting option

This commit splits the `set/show print elements' option into two.  We
retain `set/show print elements' for controlling how many elements of an
array we print, but a new `set/show print characters' setting is added
which is used for controlling how many characters of a string are
printed.

The motivation behind this change is to allow users a finer level of
control over how data is printed, reflecting that, although strings can
be thought of as arrays of characters, users often want to treat these
two things differently.

For compatibility reasons by default the `set/show print characters'
option is set to `elements', which makes the limit for character strings
follow the setting of the `set/show print elements' option, as it used
to.  Using `set print characters' with any other value makes the limit
independent from the `set/show print elements' setting, however it can
be restored to the default with the `set print characters elements'
command at any time.

A corresponding `-characters' option for the `print' command is added,
with the same semantics, i.e. one can use `elements' to make a given
`print' invocation follow the limit of elements, be it set with the
`-elements' option also given with the same invocation or taken from the
`set/show print elements' setting, for characters as well regardless of
the current setting of the `set/show print characters' option.

The GDB changes are all pretty straightforward, just changing references
to the old 'print_max' to use a new `get_print_max_chars' helper which
figures out which of the two of `print_max' and `print_max_chars' values
to use.

Likewise, the documentation is just updated to reference the new setting
where appropriate.

To make people's life easier the message shown by `show print elements'
now indicates if the setting also applies to character strings:

(gdb) set print characters elements
(gdb) show print elements
Limit on string chars or array elements to print is 200.
(gdb) set print characters unlimited
(gdb) show print elements
Limit on array elements to print is 200.
(gdb)

and the help text shows the dependency as well:

(gdb) help set print elements
Set limit on array elements to print.
"unlimited" causes there to be no limit.
This setting also applies to string chars when "print characters"
is set to "elements".
(gdb)

In the testsuite there are two minor updates, one to add `-characters'
to the list of completions now shown for the `print' command, and a bare
minimum pair of checks for the right handling of `set print characters'
and `show print characters', copied from the corresponding checks for
`set print elements' and `show print elements' respectively.

Co-Authored-By: Maciej W. Rozycki <macro@embecosm.com>
Approved-By: Simon Marchi <simon.marchi@efficios.com>

2 files changed, 8 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.base/default.exp b/gdb/testsuite/gdb.base/default.exp
index 4b1a3345f55..d0789a64401 100644
--- a/gdb/testsuite/gdb.base/default.exp
+++ b/gdb/testsuite/gdb.base/default.exp
@@ -520,6 +520,10 @@ gdb_test_no_output "set print address" "set print address"
 gdb_test_no_output "set print array" "set print array"
 #test set print asm-demangle
 gdb_test_no_output "set print asm-demangle" "set print asm-demangle"
+#test set print characters
+gdb_test "set print characters" \
+	 "Argument required \\(integer to set it to, or one of:\
+	  \"elements\", \"unlimited\"\\)\\."
 #test set print demangle
 gdb_test_no_output "set print demangle" "set print demangle"
 #test set print elements
@@ -664,6 +668,9 @@ gdb_test "show print address" "Printing of addresses is on."
 gdb_test "show print array" "Pretty formatting of arrays is on."
 #test show print asm-demangle
 gdb_test "show print asm-demangle" "Demangling of C\[+\]+/ObjC names in disassembly listings is on."
+#test show print characters
+gdb_test "show print characters" \
+	 "Limit on string characters to print is elements\\."
 #test show print demangle
 gdb_test "show print demangle" "Demangling of encoded C\[+\]+/ObjC names when displaying symbols is on."
 #test show print elements
diff --git a/gdb/testsuite/gdb.base/options.exp b/gdb/testsuite/gdb.base/options.exp
index 5a2b6d871bf..6d90615710e 100644
--- a/gdb/testsuite/gdb.base/options.exp
+++ b/gdb/testsuite/gdb.base/options.exp
@@ -172,6 +172,7 @@ proc_with_prefix test-print {{prefix ""}} {
 	"-address"
 	"-array"
 	"-array-indexes"
+	"-characters"
 	"-elements"
 	"-max-depth"
 	"-memory-tag-violations"