Date: Sun, 6 Mar 2022 17:46:44 +0900 From: Tomoaki AOKI <junchoon@dec.sakura.ne.jp> To: Dimitry Andric <dim@FreeBSD.org> Cc: John Baldwin <jhb@freebsd.org>, Ed Maste <emaste@freebsd.org>, dev-commits-src-branches@freebsd.org, David Chisnall <theraven@FreeBSD.org> Subject: Re: git: b2127b6f1ae2 - stable/13 - Install unwind.h into /usr/include Message-ID: <20220306174644.dca71df7cf1400ea48cafaca@dec.sakura.ne.jp> In-Reply-To: <682D0394-CDC8-44AB-B9FF-2B969AE2D39A@FreeBSD.org> References: <20220303224535.a0cca57e1f033e930a7f8f9d@dec.sakura.ne.jp> <3166E99F-1616-40D9-BD8B-D18E8104D6FF@FreeBSD.org> <a9863238-04e5-381d-105d-311a2b0c3f56@FreeBSD.org> <6E5AD771-3140-480A-BF20-95B8E8A27189@FreeBSD.org> <20220305113613.7760bb3845cda1c04707fb34@dec.sakura.ne.jp> <7482C54A-1128-4AFF-A74E-53D88334C1D9@FreeBSD.org> <682D0394-CDC8-44AB-B9FF-2B969AE2D39A@FreeBSD.org>
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[-- Attachment #1 --]
On Sat, 5 Mar 2022 23:33:54 +0100
Dimitry Andric <dim@FreeBSD.org> wrote:
> On 5 Mar 2022, at 22:34, Dimitry Andric <dim@FreeBSD.org> wrote:
> >
> > On 5 Mar 2022, at 03:36, Tomoaki AOKI <junchoon@dec.sakura.ne.jp> wrote:
> ...
> > So according to the spec, casting the void pointer 'thrown_exception' to
> > a __cxa_exception pointer, then subtracting 1, should give you the
> > original __cxa_exception struct. In this case, it subtracts 8 bytes,
> > going from 0x87b5aff00 to 0x87b5afe88.
>
> Ugh, actually this was 120 bytes!
>
>
> > Now I do exactly the same in the libreoffice frame one below, where the
> > incoming void pointer 'pExc' is the previous 'thrown_exception' value:
> >
> > (gdb) frame 1
> > #1 gcc3::deleteException (pExc=0x87b5aff00) at bridges/source/cpp_uno/gcc3_linux_x86-64/except.cxx:139
> > 139 OUString unoName( toUNOname( header->exceptionType->name() ) );
> > (gdb) print pExc
> > $33 = (void *) 0x87b5aff00
> > (gdb) print static_cast<__cxa_exception*>(pExc)-1
> > $34 = (__cxa_exception *) 0x87b5afe80
> >
> > So in *this* function, subtracting 1 from a __cxa_exception pointer
> > subtracts 16 bytes instead, going from 0x87b5aff00 to 0x87b5afe80!
>
> And this was 128 bytes instead. I think I now know what's going on,
> which is that our declaration of __cxa_exception changed its size from
> 120 bytes to 128 bytes, due to the new unwind headers.
>
> Our libcxxrt cxxabi.h header has:
>
> struct __cxa_exception
> {
> ... lots of stuff ...
> /** The language-agnostic part of the exception header. */
> _Unwind_Exception unwindHeader;
> };
>
> so the last field is a struct _Unwind_Exception. Our libcxxrt
> unwind-itanium.h header has:
>
> struct _Unwind_Exception
> {
> uint64_t exception_class;
> _Unwind_Exception_Cleanup_Fn exception_cleanup;
> unsigned long private_1;
> unsigned long private_2;
> } ;
>
> while libunwind's version has an __aligned__ attribute at the end:
>
> struct _Unwind_Exception {
> uint64_t exception_class;
> void (*exception_cleanup)(_Unwind_Reason_Code reason,
> _Unwind_Exception *exc);
> #if defined(__SEH__) && !defined(__USING_SJLJ_EXCEPTIONS__)
> uintptr_t private_[6];
> #else
> uintptr_t private_1; // non-zero means forced unwind
> uintptr_t private_2; // holds sp that phase1 found for phase2 to use
> #endif
> #if __SIZEOF_POINTER__ == 4
> // The implementation of _Unwind_Exception uses an attribute mode on the
> // above fields which has the side effect of causing this whole struct to
> // round up to 32 bytes in size (48 with SEH). To be more explicit, we add
> // pad fields added for binary compatibility.
> uint32_t reserved[3];
> #endif
> // The Itanium ABI requires that _Unwind_Exception objects are "double-word
> // aligned". GCC has interpreted this to mean "use the maximum useful
> // alignment for the target"; so do we.
> } __attribute__((__aligned__));
>
> (Note that upstream libcxxrt also added the reserved field and aligned
> attribute, in https://github.com/libcxxrt/libcxxrt/commit/b9616964 !)
>
> The aligned attribute on _Unwind_Exception causes the enclosing
> __cxa_exception struct to *also* be aligned maximally, growing it from
> 120 to 128 bytes on x86_64.
>
> So this is a bit of a fine mess we are in. There are multiple issues
> here:
>
> 1) We broke the ABI by increasing __cxa_exception's size.
>
> 2) We compile libcxxrt against its *own* unwind headers, so it assumes a
> 120-byte __cxa_exception size. But all other programs use the libunwind
> headers, so they assume a 128 byte __cxa_exception size.
>
> I guess LibreOffice is just a good example which breaks because it does
> this deep poking in exception-handling land, which most programs never
> go near. That said, LibreOffice also includes the unwind.h header
> installed by the libunwind-20201110 port, so that is yet *another*
> possible incompatibility!
>
> But I think we must do something about this. The most backward
> compatible change would be to *remove* the aligned attribute from our
> _Unwind_Exception declaration, so the old __cxa_exception size is
> restored. The problem with that is that we have to carry a patch for
> libunwind forever.
>
> The other way would be to force libcxxrt to use the libunwind headers
> instead of its own, so that at least libcxxrt and libunwind agree on the
> size and alignment of all these structures! But that may still lead to
> crashes for older consumers.
>
> No easy way out, in any case... :-/
>
> -Dimitry
Did a quick stupid test by
*Replacing #include "unwind.h" by #include <unwind.h> in
contrib/libcxxrt/cxxabi.h, the only file including unwind.h on
contrib/cxxrt directory to pick it from standard place.
*Rename unsind*.h to something else just to be sure.
and got errors by missing macros. At least BEGIN_PERSONALITY_FUNCTION.
Insufficient part would be needed to be extracted to additional header.
Emitted errors are as follows:
/usr/src/lib/libcxxrt# make
Building /usr/obj/usr/src/amd64.amd64/lib/libcxxrt/auxhelper.o
Building /usr/obj/usr/src/amd64.amd64/lib/libcxxrt/dynamic_cast.o
Building /usr/obj/usr/src/amd64.amd64/lib/libcxxrt/exception.o
/usr/src/contrib/libcxxrt/exception.cc:1084:1: error: unknown type name
'BEGIN_PERSONALITY_FUNCTION'
BEGIN_PERSONALITY_FUNCTION(__gxx_personality_v0) ^
/usr/src/contrib/libcxxrt/exception.cc:1084:49: error: expected ';'
after top level declarator
BEGIN_PERSONALITY_FUNCTION(__gxx_personality_v0) ^
;
/usr/src/contrib/libcxxrt/exception.cc:1098:42: error: use of
undeclared identifier 'exceptionClass'; did you mean 'exception_class'?
bool foreignException = !isCXXException(exceptionClass); ^~~~~~~~~~~~~~
exception_class
/usr/src/contrib/libcxxrt/exception.cc:242:23: note: 'exception_class'
declared here static const uint64_t exception_class =
^
/usr/src/contrib/libcxxrt/exception.cc:1101:2: error: expected
unqualified-id if (!foreignException)
^
/usr/src/contrib/libcxxrt/exception.cc:1112:91: error: use of
undeclared identifier 'context' reinterpret_cast<unsigned
char*>(static_cast<uintptr_t>(_Unwind_GetLanguageSpecificData(context)));
^ /usr/src/contrib/libcxxrt/exception.cc:1116:2: error: expected
unqualified-id if (0 == lsda_addr) { return
continueUnwinding(exceptionObject, context); } ^
/usr/src/contrib/libcxxrt/exception.cc:1137:2: error: expected
unqualified-id if (actions & _UA_SEARCH_PHASE)
^
/usr/src/contrib/libcxxrt/exception.cc:1176:2: error: expected
unqualified-id if (!(actions & _UA_HANDLER_FRAME))
^
/usr/src/contrib/libcxxrt/exception.cc:1188:2: error: expected
unqualified-id else if (foreignException)
^
/usr/src/contrib/libcxxrt/exception.cc:1195:2: error: expected
unqualified-id else if (ex->catchTemp == 0)
^
/usr/src/contrib/libcxxrt/exception.cc:1200:2: error: expected
unqualified-id else
^
/usr/src/contrib/libcxxrt/exception.cc:1209:2: error: C++ requires a
type specifier for all declarations _Unwind_SetIP(context,
reinterpret_cast<unsigned long>(action.landing_pad)); ^
/usr/src/contrib/libcxxrt/exception.cc:1209:16: error: use of
undeclared identifier 'context' _Unwind_SetIP(context,
reinterpret_cast<unsigned long>(action.landing_pad)); ^
/usr/src/contrib/libcxxrt/exception.cc:1210:2: error: C++ requires a
type specifier for all declarations _Unwind_SetGR(context,
__builtin_eh_return_data_regno(0), ^
/usr/src/contrib/libcxxrt/exception.cc:1210:16: error: use of
undeclared identifier 'context' _Unwind_SetGR(context,
__builtin_eh_return_data_regno(0), ^
/usr/src/contrib/libcxxrt/exception.cc:1211:48: error: use of
undeclared identifier 'exceptionObject' reinterpret_cast<unsigned
long>(exceptionObject)); ^
/usr/src/contrib/libcxxrt/exception.cc:1212:2: error: C++ requires a
type specifier for all declarations _Unwind_SetGR(context,
__builtin_eh_return_data_regno(1), selector); ^
/usr/src/contrib/libcxxrt/exception.cc:1212:16: error: use of
undeclared identifier 'context' _Unwind_SetGR(context,
__builtin_eh_return_data_regno(1), selector); ^
/usr/src/contrib/libcxxrt/exception.cc:1214:2: error: expected
unqualified-id return _URC_INSTALL_CONTEXT;
^
fatal error: too many errors emitted, stopping now [-ferror-limit=]
20 errors generated.
*** Error code 1
Stop.
make: stopped in /usr/src/lib/libcxxrt
.ERROR_TARGET='exception.o'
.ERROR_META_FILE='/usr/obj/usr/src/amd64.amd64/lib/libcxxrt/exception.o.meta'
.MAKE.LEVEL='0'
MAKEFILE=''
.MAKE.MODE='meta missing-filemon=yes missing-meta=yes silent=yes
verbose' _ERROR_CMD='c++ -O2 -pipe -fno-common
-isystem /usr/src/contrib/libcxxrt -nostdinc++ -march=haswell
-mretpoline -Wno-format-zero-length -fstack-protector-strong
-Wno-empty-body -Wno-string-plus-int -Wno-unused-const-variable
-Wno-error=unused-but-set-variable -Wno-tautological-compare
-Wno-unused-value -Wno-parentheses-equality -Wno-unused-function
-Wno-enum-conversion -Wno-unused-local-typedef
-Wno-address-of-packed-member -Wno-switch -Wno-switch-enum
-Wno-knr-promoted-parameter -Wno-parentheses -Qunused-arguments
-mretpoline -std=c++14 -Wno-c++11-extensions
-c /usr/src/contrib/libcxxrt/exception.cc -o
exception.o;' .CURDIR='/usr/src/lib/libcxxrt' .MAKE='make' .OBJDIR='/usr/obj/usr/src/amd64.amd64/lib/libcxxrt' .TARGETS='
all' DESTDIR='' LD_LIBRARY_PATH='' MACHINE='amd64' MACHINE_ARCH='amd64'
MAKEOBJDIRPREFIX='' MAKESYSPATH='/usr/src/share/mk'
MAKE_VERSION='20220208'
PATH='/sbin:/bin:/usr/sbin:/usr/bin:/usr/games:/usr/local/sbin:/usr/local/bin:/root/bin'
SRCTOP='/usr/src' OBJTOP='/usr/obj/usr/src/amd64.amd64'
--
Tomoaki AOKI <junchoon@dec.sakura.ne.jp>
[-- Attachment #2 --]
/usr/src/lib/libcxxrt# make
Building /usr/obj/usr/src/amd64.amd64/lib/libcxxrt/auxhelper.o
Building /usr/obj/usr/src/amd64.amd64/lib/libcxxrt/dynamic_cast.o
Building /usr/obj/usr/src/amd64.amd64/lib/libcxxrt/exception.o
/usr/src/contrib/libcxxrt/exception.cc:1084:1: error: unknown type name 'BEGIN_PERSONALITY_FUNCTION'
BEGIN_PERSONALITY_FUNCTION(__gxx_personality_v0)
^
/usr/src/contrib/libcxxrt/exception.cc:1084:49: error: expected ';' after top level declarator
BEGIN_PERSONALITY_FUNCTION(__gxx_personality_v0)
^
;
/usr/src/contrib/libcxxrt/exception.cc:1098:42: error: use of undeclared identifier 'exceptionClass'; did you mean 'exception_class'?
bool foreignException = !isCXXException(exceptionClass);
^~~~~~~~~~~~~~
exception_class
/usr/src/contrib/libcxxrt/exception.cc:242:23: note: 'exception_class' declared here
static const uint64_t exception_class =
^
/usr/src/contrib/libcxxrt/exception.cc:1101:2: error: expected unqualified-id
if (!foreignException)
^
/usr/src/contrib/libcxxrt/exception.cc:1112:91: error: use of undeclared identifier 'context'
reinterpret_cast<unsigned char*>(static_cast<uintptr_t>(_Unwind_GetLanguageSpecificData(context)));
^
/usr/src/contrib/libcxxrt/exception.cc:1116:2: error: expected unqualified-id
if (0 == lsda_addr) { return continueUnwinding(exceptionObject, context); }
^
/usr/src/contrib/libcxxrt/exception.cc:1137:2: error: expected unqualified-id
if (actions & _UA_SEARCH_PHASE)
^
/usr/src/contrib/libcxxrt/exception.cc:1176:2: error: expected unqualified-id
if (!(actions & _UA_HANDLER_FRAME))
^
/usr/src/contrib/libcxxrt/exception.cc:1188:2: error: expected unqualified-id
else if (foreignException)
^
/usr/src/contrib/libcxxrt/exception.cc:1195:2: error: expected unqualified-id
else if (ex->catchTemp == 0)
^
/usr/src/contrib/libcxxrt/exception.cc:1200:2: error: expected unqualified-id
else
^
/usr/src/contrib/libcxxrt/exception.cc:1209:2: error: C++ requires a type specifier for all declarations
_Unwind_SetIP(context, reinterpret_cast<unsigned long>(action.landing_pad));
^
/usr/src/contrib/libcxxrt/exception.cc:1209:16: error: use of undeclared identifier 'context'
_Unwind_SetIP(context, reinterpret_cast<unsigned long>(action.landing_pad));
^
/usr/src/contrib/libcxxrt/exception.cc:1210:2: error: C++ requires a type specifier for all declarations
_Unwind_SetGR(context, __builtin_eh_return_data_regno(0),
^
/usr/src/contrib/libcxxrt/exception.cc:1210:16: error: use of undeclared identifier 'context'
_Unwind_SetGR(context, __builtin_eh_return_data_regno(0),
^
/usr/src/contrib/libcxxrt/exception.cc:1211:48: error: use of undeclared identifier 'exceptionObject'
reinterpret_cast<unsigned long>(exceptionObject));
^
/usr/src/contrib/libcxxrt/exception.cc:1212:2: error: C++ requires a type specifier for all declarations
_Unwind_SetGR(context, __builtin_eh_return_data_regno(1), selector);
^
/usr/src/contrib/libcxxrt/exception.cc:1212:16: error: use of undeclared identifier 'context'
_Unwind_SetGR(context, __builtin_eh_return_data_regno(1), selector);
^
/usr/src/contrib/libcxxrt/exception.cc:1214:2: error: expected unqualified-id
return _URC_INSTALL_CONTEXT;
^
fatal error: too many errors emitted, stopping now [-ferror-limit=]
20 errors generated.
*** Error code 1
Stop.
make: stopped in /usr/src/lib/libcxxrt
.ERROR_TARGET='exception.o'
.ERROR_META_FILE='/usr/obj/usr/src/amd64.amd64/lib/libcxxrt/exception.o.meta'
.MAKE.LEVEL='0'
MAKEFILE=''
.MAKE.MODE='meta missing-filemon=yes missing-meta=yes silent=yes verbose'
_ERROR_CMD='c++ -O2 -pipe -fno-common -isystem /usr/src/contrib/libcxxrt -nostdinc++ -march=haswell -mretpoline -Wno-format-zero-length -fstack-protector-strong -Wno-empty-body -Wno-string-plus-int -Wno-unused-const-variable -Wno-error=unused-but-set-variable -Wno-tautological-compare -Wno-unused-value -Wno-parentheses-equality -Wno-unused-function -Wno-enum-conversion -Wno-unused-local-typedef -Wno-address-of-packed-member -Wno-switch -Wno-switch-enum -Wno-knr-promoted-parameter -Wno-parentheses -Qunused-arguments -mretpoline -std=c++14 -Wno-c++11-extensions -c /usr/src/contrib/libcxxrt/exception.cc -o exception.o;'
.CURDIR='/usr/src/lib/libcxxrt'
.MAKE='make'
.OBJDIR='/usr/obj/usr/src/amd64.amd64/lib/libcxxrt'
.TARGETS=' all'
DESTDIR=''
LD_LIBRARY_PATH=''
MACHINE='amd64'
MACHINE_ARCH='amd64'
MAKEOBJDIRPREFIX=''
MAKESYSPATH='/usr/src/share/mk'
MAKE_VERSION='20220208'
PATH='/sbin:/bin:/usr/sbin:/usr/bin:/usr/games:/usr/local/sbin:/usr/local/bin:/root/bin'
SRCTOP='/usr/src'
OBJTOP='/usr/obj/usr/src/amd64.amd64'
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