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https://sourceware.org/ml/gdb-patches/2014-05/msg00383.html
The MI command -var-info-path-expression currently does not handle
non-anonymous structs / unions nested within other structs / unions,
it will skip parts of the expression. Consider this example:
## START EXAMPLE ##
$ cat ex.c
#include <string.h>
int
main ()
{
struct s1
{
int a;
};
struct ss
{
struct s1 x;
};
struct ss an_ss;
memset (&an_ss, 0, sizeof (an_ss));
return 0;
}
$ gcc -g -o ex.x ex.c
$ gdb ex.x
(gdb) break 18
Breakpoint 1 at 0x80483ba: file ex.c, line 18.
(gdb) run
Starting program: /home/user/ex.x
Breakpoint 1, main () at ex.c:18
18 return 0;
(gdb) interpreter-exec mi "-var-create an_ss * an_ss"
(gdb) interpreter-exec mi "-var-list-children an_ss"
^done,numchild="1",children=[child={name="an_ss.x",exp="x",numchild="1",type="struct s1",thread-id="1"}],has_more="0"
(gdb) interpreter-exec mi "-var-list-children an_ss.x"
^done,numchild="1",children=[child={name="an_ss.x.a",exp="a",numchild="0",type="int",thread-id="1"}],has_more="0"
(gdb) interpreter-exec mi "-var-list-children an_ss.x.a"
^done,numchild="0",has_more="0"
(gdb) interpreter-exec mi "-var-info-path-expression an_ss.x.a"
^done,path_expr="(an_ss).a"
(gdb) print (an_ss).a
There is no member named a.
## END EXAMPLE ##
Notice that the path expression returned is wrong, and as a result
the print command fails.
This patch adds a new method to the varobj_ops structure called
is_path_expr_parent, to allow language specific control over finding
the parent varobj, the current logic becomes the C/C++ version and is
extended to handle the nested cases. No other language currently uses
this code, so all other languages just get a default method.
With this patch, the above example now finishes like this:
## START EXAMPLE ##
$ gdb ex.x
(gdb) break 18
Breakpoint 1 at 0x80483ba: file ex.c, line 18.
(gdb) run
Starting program: /home/user/ex.x
Breakpoint 1, main () at ex.c:18
18 return 0;
(gdb) interpreter-exec mi "-var-list-children an_ss"
^done,numchild="1",children=[child={name="an_ss.x",exp="x",numchild="1",type="struct s1",thread-id="1"}],has_more="0"
(gdb) interpreter-exec mi "-var-list-children an_ss.x"
^done,numchild="1",children=[child={name="an_ss.x.a",exp="a",numchild="0",type="int",thread-id="1"}],has_more="0"
(gdb) interpreter-exec mi "-var-list-children an_ss.x.a"
^done,numchild="0",has_more="0"
(gdb) interpreter-exec mi "-var-info-path-expression an_ss.x.a"
^done,path_expr="((an_ss).x).a"
(gdb) print ((an_ss).x).a
$1 = 0
## END EXAMPLE ##
Notice that the path expression is now correct, and the print is a
success.
gdb/ChangeLog:
* ada-varobj.c (ada_varobj_ops): Fill in is_path_expr_parent
field.
* c-varobj.c (c_is_path_expr_parent): New function, moved core
from varobj.c, with additional checks.
(c_varobj_ops): Fill in is_path_expr_parent field.
(cplus_varobj_ops): Fill in is_path_expr_parent field.
* jv-varobj.c (java_varobj_ops): Fill in is_path_expr_parent
field.
* varobj.c (is_path_expr_parent): Call is_path_expr_parent varobj
ops method.
(varobj_default_is_path_expr_parent): New function.
* varobj.h (lang_varobj_ops): Add is_path_expr_parent field.
(varobj_default_is_path_expr_parent): Declare new function.
gdb/testsuite/ChangeLog:
* gdb.mi/var-cmd.c (do_nested_struct_union_tests): New function
setting up test structures.
(main): Call new test function.
* gdb.mi/mi2-var-child.exp: Create additional breakpoint in new
test function, continue into test function and walk test
structures.
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* Makefile.in (SFILES): Add c-varobj.c and jv-varobj.c.
(COMMON_OBS): Add c-varobj.o and jv-varobj.o.
* ada-varobj.c: Include "varobj.h".
(ada_number_of_children): New. Moved from varobj.c.
(ada_name_of_variable, ada_name_of_child): Likewise.
(ada_path_expr_of_child, ada_value_of_child): Likewise.
(ada_type_of_child, ada_value_of_variable): Likewise.
(ada_value_is_changeable_p, ada_value_has_mutated): Likewise.
(ada_varobj_ops): New.
* c-varobj.c, jv-varobj.c: New file. Moved from varobj.c.
* gdbtypes.c (get_target_type): New. Moved from varobj.c.
* gdbtypes.h (get_target_type): Declare.
* varobj.c: Remove the inclusion of "ada-varobj.h" and
"ada-lang.h".
(ANONYMOUS_STRUCT_NAME): Move it to c-varobj.c.
(ANONYMOUS_UNION_NAME): Likewise.
(get_type, get_value_type, get_target_type): Remove declarations.
(value_get_print_value, varobj_value_get_print_value): Likewise.
(c_number_of_children, c_name_of_variable): Likewise.
(c_name_of_child, c_path_expr_of_child): Likewise.
(c_value_of_child, c_type_of_child): Likewise.
(c_value_of_variable, cplus_number_of_children): Likewise.
(cplus_class_num_children, cplus_name_of_variable): Likewise.
(cplus_name_of_child, cplus_path_expr_of_child): Likewise.
(cplus_value_of_child, cplus_type_of_child): Likewise.
(cplus_value_of_variable, java_number_of_children): Likewise.
(java_name_of_variable, java_name_of_child): Likewise.
(java_path_expr_of_child, java_value_of_child): Likewise.
(java_type_of_child, java_value_of_variable): Likewise.
(ada_number_of_children, ada_name_of_variable): Likewise.
(ada_name_of_child, ada_path_expr_of_child): Likewise.
(ada_value_of_child, ada_type_of_child): Likewise.
(ada_value_of_variable, ada_value_is_changeable_p): Likewise.
(ada_value_has_mutated): Likewise.
(struct language_specific): Move it to varobj.h.
(CPLUS_FAKE_CHILD): Move it to varobj.h.
(restrict_range): Rename it varobj_restrict_range. Make it extern.
Callers update.
(get_path_expr_parent): Rename it to varobj_get_path_expr_parent.
Make it extern.
(is_anonymous_child): Move it to c-varobj.c and rename to
varobj_is_anonymous_child. Caller update.
(get_type): Move it to c-varobj.c.
(get_value_type): Rename it varobj_get_value_type. Make it
extern.
(get_target_type): Move it gdbtypes.c.
(varobj_formatted_print_options): New function.
(value_get_print_value): Rename it to
varobj_value_get_print_value and make it extern.
(varobj_value_is_changeable_p): Make it extern.
(adjust_value_for_child_access): Move it to c-varobj.c.
(default_value_is_changeable_p): Rename it to
varobj_default_value_is_changeable_p. Make it extern.
(c_number_of_children, c_name_of_variable): Move it to c-varobj.c
(c_name_of_child, c_path_expr_of_child): Likewise.
(c_value_of_child, c_type_of_child): Likewise.
(c_value_of_variable, cplus_number_of_children): Likewise.
(cplus_class_num_children, cplus_name_of_variable): Likewise.
(cplus_name_of_child, cplus_path_expr_of_child): Likewise.
(cplus_value_of_child, cplus_type_of_child): Likewise.
(cplus_value_of_variable): Likewise.
(java_number_of_children, java_name_of_variable): Move it to jv-varobj.c.
(java_name_of_child, java_path_expr_of_child): Likewise.
(java_value_of_child, java_type_of_child): Likewise.
(java_value_of_variable): Likewise.
(ada_number_of_children, ada_name_of_variable): Move it to ada-varobj.c.
(ada_name_of_child, ada_path_expr_of_child): Likewise.
(ada_value_of_child, ada_type_of_child): Likewise.
(ada_value_of_variable, ada_value_is_changeable_p): Likewise.
(ada_value_has_mutated): Likewise.
* varobj.h (CPLUS_FAKE_CHILD): New macro, moved from varobj.c.
(struct lang_varobj_ops): New. Renamed by 'struct language_specific'.
(c_varobj_ops, cplus_varobj_ops): Declare.
(java_varobj_ops, ada_varobj_ops): Declare.
(varobj_default_value_is_changeable_p): Declare.
(varobj_value_is_changeable_p): Declare.
(varobj_get_value_type, varobj_is_anonymous_child): Declare.
(varobj_get_path_expr_parent): Declare.
(varobj_value_get_print_value): Declare.
(varobj_formatted_print_options): Declare.
(varobj_restrict_range): Declare.
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