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Date: Sat, 19 Mar 2022 09:44:14 +0100
From: Szabolcs Nagy <nsz@port70.net>
To: "Kenny, Joseph P" <jpkenny@sandia.gov>
Cc: "musl@lists.openwall.com" <musl@lists.openwall.com>
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Subject: Re: [musl] Re: [EXTERNAL] [musl] C++ segfault on riscv64

* Kenny, Joseph P <jpkenny@sandia.gov> [2022-03-18 16:48:11 +0000]:
> Sorry for the confusing post. I get the same behavior on qemu for both ri=
scv64 and riscv32. I posted output from riscv32.
>=20
> Here is the C++ code:
> $ cat hello.cc
> #include <iostream>
> int main() {
> std::cout << "Hello\n";
> return 0;
> }
>=20
> From: "Kenny, Joseph P" <jpkenny@sandia.gov>
> Reply-To: "musl@lists.openwall.com" <musl@lists.openwall.com>
> Date: Friday, March 18, 2022 at 9:42 AM
> To: "musl@lists.openwall.com" <musl@lists.openwall.com>
> Subject: [EXTERNAL] [musl] C++ segfault on riscv64
>=20
> I=E2=80=99m getting segfaults with musl for C++ code on riscv64. I have t=
ested mipsel using qemu user mode as described below and found no issues.
>=20
> I=E2=80=99m cross-compiling using the latest riscv64-linux-musl-cross.tgz=
 (23-Nov-2021) from musl.cc on x86_64/Fedora 35. I have confirmed that I ge=
t the following behavior for both riscv64 hardware and qemu user mode.
=2E..
> C++ segfaults:
>=20
> $ riscv32-linux-musl-g++ -static -g -Og hello.cc -o hello
> $ qemu-riscv32 hello
> Segmentation fault (core dumped)
>=20
> GDB confirms the segfault in __dynamic_cast on both qmeu and riscv64 hard=
ware. I=E2=80=99ll paste in the assembly below. Segfault occurs on the last=
 instruction shown [ld      a5,0(a0)].
>=20
> I=E2=80=99ve taken this as far as my skills allow. Any ideas what=E2=80=
=99s going on here or how to debug further?

listdc++ iostreams initializers call __dynamic_cast many times (this is
all in libstdc++, nothing to do with musl).

you need to figure out which cast fails and why the type info is corrupt.

e.g. build libstdc++ with debug info and printing the backtrace may help.