Re https://sourceware.org/gdb/current/onlinedocs/gdb/Types-In-Python.html We've had numerous libstdc++ bugs in the python printers that are due to me failing to use the right string representation of a type. I find it unclear whether I should use gdb.Type.name (which isn't present in older GDB versions) or gdb.Type.tag or str(gdb.Type). The docs do not really say what the various strings contain, particularly for C++ class types, with possible cv-qualifiers present. The conversion to String is completely undocumented. On IRC I was told that it's similar to whatis/r s, which seems to be true. I'm told that for some combinations of GCC and GDB that string includes "class", which means it isn't suitable as an argument to the gdb.lookup_type function. It doesn't drop cv-qualifiers, e.g. (gdb) py print(gdb.lookup_type('int').const()) const int The difference between gdb.Type.name and gdb.Type.tag is unclear, except that gdb.Type.name doesn't exist in older GDB versions (which could be documented too), and for non-class types (e.g. integer types and functions) there is no tag e.g. (gdb) py print(gdb.lookup_type('int').tag) None (gdb) py print(gdb.lookup_type('int').name) int As far as I can tell, both drop cv-qualifiers: (gdb) py print(gdb.lookup_type('int').const().name) int They seem to be the same for class and enumeration types. But a typedef for a class has a name but no tag, which makes sense, but could be stated explicitly. Given: int main() { struct S {} s; using C = const S; C c = S(); return 0; } I get this with GDB 9.1: $ gdb -q -ex start a.out Reading symbols from a.out... Temporary breakpoint 1 at 0x401106: file test.C, line 6. Starting program: /tmp/a.out Temporary breakpoint 1, main () at test.C:6 6 return 0; (gdb) py s = gdb.parse_and_eval('s'); c = gdb.parse_and_eval('c') (gdb) py print(s.type) S (gdb) py print(s.type.tag) S (gdb) py print(s.type.name) S (gdb) py print(c.type) C (gdb) py print(c.type.tag) None (gdb) py print(c.type.name) C (gdb) py print(c.type.strip_typedefs()) const S (gdb) py print(c.type.strip_typedefs().name) S (gdb) py print(c.type.strip_typedefs().tag) S
Created attachment 13283 [details] Patch for python.texi I think this addresses all my comments above, assuming I've understood the semantics correctly.
But to make things more complicated ... echo 'struct S { } s;' > test.C g++ -g -c test.C -o test1.o echo 'int main() { }' >> test.C g++ -g -c test.C -o test2.o gdb -q -ex 'py print(gdb.lookup_type("S"))' -ex q test1.o Reading symbols from test1.o... struct S gdb -q -ex 'py print(gdb.lookup_type("S"))' -ex q test2.o Reading symbols from test2.o... S WAT? Whether str(gdb.Type) includes the "struct" class-head depends on whether main() is defined in the same translation unit? How does that make sense? It is at least consistent with 'whatis': gdb -q -ex 'whatis s' -ex q test1.o Reading symbols from test1.o... type = struct S gdb -q -ex 'whatis s' -ex q test2.o Reading symbols from test2.o... type = S But ... why?
(In reply to Jonathan Wakely from comment #2) > But to make things more complicated ... > > echo 'struct S { } s;' > test.C > g++ -g -c test.C -o test1.o > echo 'int main() { }' >> test.C > g++ -g -c test.C -o test2.o > > gdb -q -ex 'py print(gdb.lookup_type("S"))' -ex q test1.o > Reading symbols from test1.o... > struct S > > gdb -q -ex 'py print(gdb.lookup_type("S"))' -ex q test2.o > Reading symbols from test2.o... > S > > WAT? > > Whether str(gdb.Type) includes the "struct" class-head depends on whether > main() is defined in the same translation unit? How does that make sense? This behavior started with gdb-8.2, with 8.1.1 it says just 'S' for both.