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From: Christian Franke <Christian DOT Franke AT t-online DOT de>
Subject: [PATCH] cygutils-extra 1.4.16-3: cygdrop: Fix crash
To: cygwin AT cygwin DOT com
Message-ID: <2f5eedb0-b3ec-4c4e-5740-5196e2572dc7@t-online.de>
Date: Sat, 14 Aug 2021 15:39:15 +0200
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Cygdrop from recent cygutils-extra crashes (only) after printing help tex=
t:

$ cygdrop
Usage: cygdrop [OPTIONS] COMMAND [ARG ...]

Group options
 =C2=A0 -l=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Disable local admini=
strator group [default]
...
 =C2=A0 -v=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Verbose output, list=
s groups and privileges changed.
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Repea=
t to list all groups and privileges.

*** stack smashing detected ***: terminated
Aborted (core dumped)


The root of the problem is a usually harmless bug introduced in 2010. A=20
function return type was declared as 'int' instead of 'void':
https://sourceware.org/git/?p=3Dcygwin-apps/cygutils.git;a=3Dcommitdiff;h=
=3D517cf61

Newer g++ may then optimize away the function epilogue after inline=20
expansion. Here is a minimal testcase:

$ g++ --version
g++ (GCC) 10.2.0
...

$ cat test.cc
void f();

static int g()
{
 =C2=A0 f();
}

void h()
{
 =C2=A0 g();
}

$ g++ -S -O test.cc
test.cc: In function =E2=80=98int g()=E2=80=99:
test.cc:6:1: warning: no return statement in function returning non-void=20
[-Wreturn-type]
 =C2=A0=C2=A0=C2=A0 6 | }
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 | ^

$ c++filt < test.s
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 .file=C2=A0=C2=A0 "test.cc"
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 .text
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 .globl=C2=A0 h()
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 .def=C2=A0=C2=A0=C2=A0 h();=C2=
=A0=C2=A0=C2=A0 .scl=C2=A0=C2=A0=C2=A0 2;=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 .=
type=C2=A0=C2=A0 32; .endef
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 .seh_proc=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0 h()
h():
.LFB1:
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 subq=C2=A0=C2=A0=C2=A0 $40, %=
rsp
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 .seh_stackalloc 40
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 .seh_endprologue
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 call=C2=A0=C2=A0=C2=A0 f()
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 nop
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 .seh_endproc
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 .ident=C2=A0 "GCC: (GNU) 10.2=
.0"
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 .def=C2=A0=C2=A0=C2=A0 f();=C2=
=A0=C2=A0=C2=A0 .scl=C2=A0=C2=A0=C2=A0 2;=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 .=
type=C2=A0=C2=A0 32; .endef



Problem and -Wreturn-type do not occur if compiled as a C program:

$ g++ -xc -S -O test.cc

$ cat test.s
...
h:
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 subq=C2=A0=C2=A0=C2=A0 $40, %=
rsp
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 .seh_stackalloc 40
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 .seh_endprologue
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 call=C2=A0=C2=A0=C2=A0 f
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 nop
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 addq=C2=A0=C2=A0=C2=A0 $40, %=
rsp
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ret
 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 .seh_endproc
...


The problem also occurs with 32-bit Cygwin g++ and with current=20
MinGW-w64-g++ 32/64-bit.

Unfortunately GCC upstream has already set a related bug report to INVALI=
D:
 =C2=A0https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96181
I disagree...

Cygport should possibly add '-Werror=3Dreturn-type' to C++ defaults.


Patch for cygutils is attached.

Regards,
Christian


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