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c3efaf0afd
When the source program contains a goto label, it turns out it's
actually pretty hard for a user to find out more about that label.
For example:
(gdb) p some_label
No symbol "some_label" in current context.
(gdb) disassemble some_label
No symbol "some_label" in current context.
(gdb) x/10i some_label
No symbol "some_label" in current context.
(gdb) break some_label
Breakpoint 2 at 0x401135: file /tmp/py-label-symbol-value.c, line 35.
In all cases, some_label is a goto label within the current frame.
Only placing a breakpoint on the label worked.
This all seems a little strange to me, it feels like asking about a
goto label would not be an unreasonable thing for a user to do.
This commit doesn't fix any of the above issues, I mention them just
to provide a little context for why the following issue has probably
not been seen before.
It turns out there is one way a user can access the symbol for a goto
label, through the Python API:
python frame = gdb.selected_frame()
python frame_pc = frame.pc()
python block = gdb.current_progspace().block_for_pc(frame_pc)
python symbol,_ = gdb.lookup_symbol('some_label', block, gdb.SYMBOL_LABEL_DOMAIN)
python print(str(symbol.value()))
../../src/gdb/findvar.c:204: internal-error: store_typed_address: Assertion `type->is_pointer_or_reference ()' failed.
The problem is that label symbols are created using the
builtin_core_addr type, which is a pure integer type.
When GDB tries to fetch the value of a label symbol then we end up in
findvar.c, in the function language_defn::read_var_value, in the
LOC_LABEL case. From here store_typed_address is called to store the
address of the label into a value object with builtin_core_addr type.
The problem is that store_typed_address requires that the destination
type be a pointer or reference, which the builtin_core_addr type is
not.
Now it's not clear what type a goto label address should have, but
GCC has an extension that allows users to take the address of a goto
label (using &&), in that case the result is of type 'void *'.
I propose that when we convert the CORE_ADDR value to a GDB value
object, we use builtin_func_ptr type instead of builtin_core_addr,
this means the result will be of type 'void (*) ()'. The benefit of
this approach is that when gdbarch_address_to_pointer is called the
target type will be correctly identified as a pointer to code, which
should mean any architecture specific adjustments are done correctly.
We can then cast the new value to 'void *' type with a call to
value_cast_pointer, this should not change the values bit
representation, but will just update the type.
After this asking for the value of a label symbol works just fine:
(gdb) python print(str(symbol.value()))
0x401135 <main+35>
And the type is maybe what we'd expect:
(gdb) python print(str(symbol.value().type))
void *
README for GNU development tools This directory contains various GNU compilers, assemblers, linkers, debuggers, etc., plus their support routines, definitions, and documentation. If you are receiving this as part of a GDB release, see the file gdb/README. If with a binutils release, see binutils/README; if with a libg++ release, see libg++/README, etc. That'll give you info about this package -- supported targets, how to use it, how to report bugs, etc. It is now possible to automatically configure and build a variety of tools with one command. To build all of the tools contained herein, run the ``configure'' script here, e.g.: ./configure make To install them (by default in /usr/local/bin, /usr/local/lib, etc), then do: make install (If the configure script can't determine your type of computer, give it the name as an argument, for instance ``./configure sun4''. You can use the script ``config.sub'' to test whether a name is recognized; if it is, config.sub translates it to a triplet specifying CPU, vendor, and OS.) If you have more than one compiler on your system, it is often best to explicitly set CC in the environment before running configure, and to also set CC when running make. For example (assuming sh/bash/ksh): CC=gcc ./configure make A similar example using csh: setenv CC gcc ./configure make Much of the code and documentation enclosed is copyright by the Free Software Foundation, Inc. See the file COPYING or COPYING.LIB in the various directories, for a description of the GNU General Public License terms under which you can copy the files. REPORTING BUGS: Again, see gdb/README, binutils/README, etc., for info on where and how to report problems.