Interesting... What lldb & clang were you using? With current TOT clang &
lldb I see:
(lldb) run
Process 83732 launched: '/tmp/template2' (x86_64)
Process 83732 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
frame #0: 0x0000000100000fad template2`main at template.cpp:12
9
10 int main() {
11 foo<void> test2;
-> 12 return 0;
^
13 }
(lldb) expr sizeof(test)
(unsigned long) $0 = 4
(lldb) expr sizeof(test2)
(unsigned long) $1 = 4
That's good, we do know about both of these, but:
(lldb) expr sizeof(foo<void>)
error: use of undeclared identifier 'foo'
error: expected '(' for function-style cast or type construction
error: expected expression
(lldb) expr sizeof(foo<int>)
error: use of undeclared identifier 'foo'
error: expected '(' for function-style cast or type construction
error: expected expression
Jim
> On Jul 23, 2019, at 5:49 PM, Scott Funkenhauser <sfunkenhau...@google.com>
> wrote:
>
> I built with both clang and gcc, the behavior is the same (lldb fails to
> evaluate the expression, gdb succeeds).
>
> Trying to evaluate a template type that hasn't been instantiated fails in
> both lldb and gdb.
> ie.
> (gdb) p sizeof(foo<double>)
> No symbol "foo<double>" in current context.
> (lldb) p sizeof(foo<double>)
> error: implicit instantiation of undefined template 'foo<double>'
> template is declared here
>
> Looking at the debug info, both template instantiations are there, it seems
> like LLDB just isn't finding it (while GDB is).
>
> $readelf --debug-dump a.out | grep foo
> 0x00000000 666f6f00 5400696e 7400666f 6f3c696e foo.T.int.foo<in
> 0x00000080 00746573 74320066 6f6f3c76 6f69643e .test2.foo<void>
> <41> DW_AT_name : (indirect string, offset: 0xa): foo<int>
> <49> DW_AT_name : (indirect string, offset: 0x0): foo
> <8f> DW_AT_name : (indirect string, offset: 0x87): foo<void>
> <97> DW_AT_name : (indirect string, offset: 0x0): foo
> 8d foo<void>
> 3f foo<int>
>
> On Tue, Jul 23, 2019 at 8:35 PM Jim Ingham <jing...@apple.com> wrote:
> lldb can't currently create new template instantiations. It can only access
> ones that were generated in the binary you were debugging. The debug
> information doesn't have any code, so we can't create new instantiations from
> there. Having the debugger try to include headers into the expression
> context in the same way the compiler did originally is also tricky since we
> don't know the header search paths or defines that the compiler used when it
> built the template instantiations... Raphael has been working on doing this
> for the case where the C++ code is build into a clang module, but I don't
> think that work is done yet, and then you have to build your code with
> modules to use it...
>
> The <int> expression is failing because clang is being smart and sees that
> though you mention foo<int> in reference to "test" you never actually use
> "test", so it doesn't actually have to make that instantiation. In the case
> where this works with gdb, did you build with clang or did you build with
> gcc? If the latter, this might be working for gdb because gcc emits code for
> the int template instantiation when you mention it, rather than only when you
> use it?
>
> Does it also work for gdb when you try:
>
> (gdb) p sizeof(foo<double>)
>
> or any other type you haven't mentioned in your code?
>
> Not that that really matters for what lldb would have to do, but it would be
> interesting to know...
>
> Jim
>
>
>
> > On Jul 23, 2019, at 4:22 PM, Scott Funkenhauser via lldb-dev
> > <lldb-dev@lists.llvm.org> wrote:
> >
> > Hey,
> >
> > I've noticed that evaluating expressions involving templated classes seems
> > to have some unexpected behavior.
> >
> > I've created the following sample code to reproduce the issue:
> >
> > template <typename T> class foo
> > {
> > uint32_t data;
> > };
> >
> > foo<int> test;
> >
> > int main() {
> > foo<void> test2;
> > return 0;
> > }
> >
> > I've set a breakpoint on main and evaluated the following expressions:
> > (lldb) p sizeof(foo<void>)
> > (unsigned long) $0 = 4
> > (lldb) p sizeof(foo<int>)
> > error: implicit instantiation of undefined template 'foo<int>'
> > template is declared here
> >
> > It seems like expression evaluation can only find the specialized templated
> > classes that were used in the current scope. Running the same example using
> > GDB works as expected (both expressions are evaluated correctly).
> >
> > Is this a known issue?
> > Does anybody have any insight, or familiarity with expression evaluation
> > that would be able to point me in the right direction?
> >
> > Thanks,
> > Scott
> > _______________________________________________
> > lldb-dev mailing list
> > lldb-dev@lists.llvm.org
> > https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
>
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