[PATCH 19/36] Exported const objects

Pedro Alves
2015-02-09T23:21:41Z

const works different in C vs C++. In C++, a global "const" variable
has internal linkage by default, resulting in link errors like:

...
extension.o: In function `get_ext_lang_defn(extension_language)':
gdb/extension.c:126: undefined reference to `extension_language_guile'
gdb/extension.c:124: undefined reference to `extension_language_guile'
...

The fix is to define exported const objects with "extern const". But
that in C would not be a definition. So we need to #ifdef C vs C++ in
this case.

EXPORTED_CONST comes from include/ansidecl.h, but in the
feature_to_c.sh case I think it's better to leave the script with no
dependencies.

gdb/ChangeLog:
2015-02-09 Pedro Alves <palves@redhat.com>

* cp-valprint.c (vtbl_ptr_name): Use EXPORTED_CONST.
* guile/guile.c (extension_language_guile): Use EXPORTED_CONST.
* features/feature_to_c.sh: Tag the generated xml_builtin array
with extern const in C++ mode.
---
gdb/cp-valprint.c | 2 +-
gdb/features/feature_to_c.sh | 8 +++++++-
gdb/guile/guile.c | 2 +-
3 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/gdb/cp-valprint.c b/gdb/cp-valprint.c
index 93f4c1b..0ddc96e 100644
--- a/gdb/cp-valprint.c
+++ b/gdb/cp-valprint.c
@@ -88,7 +88,7 @@ static void cp_print_value (struct type *, struct type *,

/* GCC versions after 2.4.5 use this. */
-const char vtbl_ptr_name[] = "__vtbl_ptr_type";
+EXPORTED_CONST char vtbl_ptr_name[] = "__vtbl_ptr_type";

/* Return truth value for assertion that TYPE is of the type
"pointer to virtual function". */
diff --git a/gdb/features/feature_to_c.sh b/gdb/features/feature_to_c.sh
index fb37a6b..35db791 100644
--- a/gdb/features/feature_to_c.sh
+++ b/gdb/features/feature_to_c.sh
@@ -63,7 +63,13 @@ for input; do
done

echo >> $output
-echo "const char *const xml_builtin[][2] = {" >> $output
+
+echo "#ifdef __cplusplus" >> $output
+echo "# define EXPORTED_CONST extern const" >> $output
+echo "#else" >> $output
+echo "# define EXPORTED_CONST const" >> $output
+echo "#endif" >> $output
+echo "EXPORTED_CONST char *const xml_builtin[][2] = {" >> $output

for input; do
basename=`echo $input | sed 's,.*/,,'`
diff --git a/gdb/guile/guile.c b/gdb/guile/guile.c
index 3e0d11a..1895118 100644
--- a/gdb/guile/guile.c
+++ b/gdb/guile/guile.c
@@ -77,7 +77,7 @@ extern const struct extension_language_ops guile_extension_ops;

/* The main struct describing GDB's interface to the Guile
extension language. */
-const struct extension_language_defn extension_language_guile =
+EXPORTED_CONST struct extension_language_defn extension_language_guile =
{
EXT_LANG_GUILE,
"guile",
--
1.9.3