aeubanks added a comment.
In D137983#3930973 <https://reviews.llvm.org/D137983#3930973>, @labath wrote:
> We have tests for shared libraries (grep for DYLIB_C(XX)_SOURCES)), but it's
> easier to reproduce this problem by compiling one CU with -g0 -- see inline
> comment. (If you are creating an "API" test for this, beware that their
> default is to build everything with -fstandalone-debug, and you'll need to
> explicitly change that (see LIMIT_DEBUG_INFO_FLAGS))
`lldb/test/API/lang/cpp/incomplete-types/` looks like exactly what I want, I've
added a test based on that (and verified that lldb crashes in that test without
the source change)
> This behavior (bug) is triggered by the `FrontEndWantsDereference` formatter
> flag, which is why it manifests itself for (libc++) vector and friends. The
> ObjC formatters don't set that flag so they should be safe. The libstdc++
> formatters don't set it either. Furthermore there doesn't seem to be a way to
> set this flag by the user, so it is not possible to create a
> libc++-independent reproducer (which is what I was going to suggest).
>
> I've been looking for a better way to fix this today (sorry about the delay),
> but I haven't figured out anything better. There is this fundamental
> recursion between the pretty printer (which wants to dereference a value) and
> the dereferencing code (which wants to know if it has a pretty printer -- so
> it can avoid dereferencing). Just removing the `HasSyntheticValue()`fixed the
> bug for me -- but then we were able to "dereference" incomplete structs. It's
> possible we may be able to allow the dereference to succeed here, but then
> refuse to print the value somewhere down the line. I would like to hear what
> @jingham things about all this.
Thanks for the investigation!
Actually some libstdc++ formatters do also set `FrontEndWantsDereference`, so
this is reproable with
$ cat /tmp/main.cc
#include <set>
void f(std::set<int>& v);
int main() {
std::set<int> v;
f(v);
}
$ cat /tmp/a.cc
#include <set>
void f(std::set<int>& v) {
// break
}
$ bin/clang++ -g0 /tmp/main.cc -o /tmp/main.o -c && bin/clang++ -g /tmp/a.cc
-o /tmp/a.o -c && bin/clang++ /tmp/a.o /tmp/main.o -o /tmp/a
$ bin/lldb /tmp/a -b -o 'br set -n f' -o run
with and without `-stdlib=libc++`
maybe a more targeted solution would be to change the added condition to when
`FrontEndWantsDereference` is set, but that's more annoying to thread through
the code. I think this should be ok as a temporary workaround if we don't have
a proper fix soonish?
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D137983/new/
https://reviews.llvm.org/D137983
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