powerpc64 head -r345044: WITH_LLVM_LIBUNWIND= based buildworld leads to thrown C++ exceptions segmentation faulting
Mark Millard
marklmi at yahoo.com
Tue Mar 12 21:05:36 UTC 2019
[I got some libunwind debug output from the a.out run. This
and a disassembly of main suggest an instruction pointer
address is too large by 0x4 for jumping to the code that
would call __cxa_begin_catch .]
> On 2019-Mar-12, at 12:20, Mark Millard <marklmi at yahoo.com> wrote:
>
> [I sometimes experiment with building powerpc64 (and 32-bit) via
> more modern toolchains, here a amd64->powerpc64 cross build via
> system-clang (so 8.0.0).]
>
> buildworld with WITH_LLVM_LIBUNWIND= completes for powerpc64
> (but not 32-bit powerpc). However, for a system installed
> from such for pwoerpc64, the following program (for example)
> gets a segmentation fault:
>
> # more ~/c_tests/exception_test.cpp
> #include <exception>
>
> int main(void)
> {
> try { throw std::exception(); }
> catch (std::exception& e) {}
> return 0;
> }
>
> (Note: the same a.out works under a WITHOUT_LLVM_LIBUNWIND=
> environment, that was patched for DW_CFA_remember_state and
> DW_CFA_restore_state handling, with the system built via
> devel/powerpc64-xtoolchain-gcc related materials. So the
> failure is on the system library does of things for the
> WITH_LLVM_LIBUNWIND= context.)
>
> Unfortunately:
>
> A) devel/gdb makes extensive use of thrown C++ exceptions
> and so does not work for a powerpc64 system based on
> WITH_LLVM_LIBUNWIND= .
>
> B) The world built is not using dwarf-2 so /usr/libexec/gdb
> is not handy/useful.
>
> C) CFLAGS+=-gdwarf-2 leads to system-clang having an Abort
> trap during buildworld's compile of gcrt1.s . (Reference
> material later, below.)
>
> D) lldb crashes in llvm_unreachable in
> lldb::RegisterContextSP FreeBSDThread::GetRegisterContext()
> on powerpc64. (Reference material later, below.)
>
> So I've not managed to check the backtrace for the
> segmentation fault in the short example.
>
>
>
> For reference . . .
>
>
> For (C) ( -gdwarf-2 use ):
>
> QUOTES
> (gdb) bt
> #0 thr_kill () at thr_kill.S:3
> #1 0x000000000474afcf in __raise (s=6) at /usr/src/lib/libc/gen/raise.c:52
> #2 0x00000000046cd386 in abort () at /usr/src/lib/libc/stdlib/abort.c:79
> #3 0x00000000047394ba in __assert (func=<optimized out>, file=<optimized out>, line=<optimized out>, failedexpr=<optimized out>) at /usr/src/lib/libc/gen/assert.c:51
> #4 0x000000000429aa9f in resetRootFile () at /usr/src/contrib/llvm/include/llvm/MC/MCDwarf.h:316
> #5 parseDirectiveFile () at /usr/src/contrib/llvm/lib/MC/MCParser/AsmParser.cpp:3377
> #6 parseStatement () at /usr/src/contrib/llvm/lib/MC/MCParser/AsmParser.cpp:2023
> #7 0x000000000428cc12 in Run () at /usr/src/contrib/llvm/lib/MC/MCParser/AsmParser.cpp:884
> #8 0x000000000163c649 in ExecuteAssembler () at /usr/src/contrib/llvm/tools/clang/tools/driver/cc1as_main.cpp:503
> #9 cc1as_main () at /usr/src/contrib/llvm/tools/clang/tools/driver/cc1as_main.cpp:589
> #10 0x0000000001643d10 in ExecuteCC1Tool () at /usr/src/contrib/llvm/tools/clang/tools/driver/driver.cpp:312
> #11 main () at /usr/src/contrib/llvm/tools/clang/tools/driver/driver.cpp:382
>
> void resetRootFile() {
> assert(Header.MCDwarfFiles.empty());
> Header.RootFile.Name.clear();
> Header.resetMD5Usage();
> Header.HasSource = false;
> }
>
> --- lib/csu__L ---
> cc: error: unable to execute command: Abort trap (core dumped)
> cc: error: clang integrated assembler command failed due to signal (use -v to see invocation)
> FreeBSD clang version 8.0.0 (branches/release_80 355677) (based on LLVM 8.0.0)
> Target: powerpc64-unknown-freebsd13.0
> Thread model: posix
> InstalledDir: /usr/bin
> cc: note: diagnostic msg: PLEASE submit a bug report to https://bugs.freebsd.org/submit/ and include the crash backtrace, preprocessed source, and associated run script.
> cc: note: diagnostic msg: Error generating preprocessed source(s) - no preprocessable inputs.
> *** [gcrt1.o] Error code 254
>
> make[5]: stopped in /usr/src/lib/csu/powerpc64
> .ERROR_TARGET='gcrt1.o'
> .ERROR_META_FILE='/usr/obj/powerpc64vtsc_clang_altbinutils/powerpc.powerpc64/usr/src/powerpc.powerpc64/lib/csu/powerpc64/gcrt1.o.meta'
> .MAKE.LEVEL='5'
> MAKEFILE=''
> .MAKE.MODE='meta missing-filemon=yes missing-meta=yes silent=yes verbose'
> _ERROR_CMD='cc -gdwarf-2 -target powerpc64-unknown-freebsd13.0 --sysroot=/usr/obj/powerpc64vtsc_clang_altbinutils/powerpc.powerpc64/usr/src/powerpc.powerpc64/tmp -B/usr/local/powerpc64-unknown-freebsd13.0/bin/ -O2 -pipe -I/usr/src/lib/csu/common -I/usr/src/lib/libc/include -mlongcall -DCRT_IRELOC_SUPPRESS -std=gnu99 -Wsystem-headers -Wall -Wno-format-y2k -W -Wno-unused-parameter -Wstrict-prototypes -Wmissing-prototypes -Wpointer-arith -Wreturn-type -Wcast-qual -Wwrite-strings -Wswitch -Wshadow -Wunused-parameter -Wcast-align -Wchar-subscripts -Winline -Wnested-externs -Wredundant-decls -Wold-style-definition -Wno-pointer-sign -Wthread-safety -Wno-empty-body -Wno-string-plus-int -Wno-unused-const-variable -Qunused-arguments -c -o gcrt1.o gcrt1.s;'
> .CURDIR='/usr/src/lib/csu/powerpc64'
> .MAKE='make'
> .OBJDIR='/usr/obj/powerpc64vtsc_clang_altbinutils/powerpc.powerpc64/usr/src/powerpc.powerpc64/lib/csu/powerpc64'
> .TARGETS='all'
> DESTDIR='/usr/obj/powerpc64vtsc_clang_altbinutils/powerpc.powerpc64/usr/src/powerpc.powerpc64/tmp'
> LD_LIBRARY_PATH=''
> MACHINE='powerpc'
> MACHINE_ARCH='powerpc64'
> MAKEOBJDIRPREFIX=''
> MAKESYSPATH='/usr/src/share/mk'
> MAKE_VERSION='20181221'
> PATH='/usr/obj/powerpc64vtsc_clang_altbinutils/powerpc.powerpc64/usr/src/powerpc.powerpc64/tmp/usr/sbin:/usr/obj/powerpc64vtsc_clang_altbinutils/powerpc.powerpc64/usr/src/powerpc.powerpc64/tmp/usr/bin:/usr/obj/powerpc64vtsc_clang_altbinutils/powerpc.powerpc64/usr/src/powerpc.powerpc64/tmp/legacy/usr/sbin:/usr/obj/powerpc64vtsc_clang_altbinutils/powerpc.powerpc64/usr/src/powerpc.powerpc64/tmp/legacy/usr/bin:/usr/obj/powerpc64vtsc_clang_altbinutils/powerpc.powerpc64/usr/src/powerpc.powerpc64/tmp/legacy/bin::/sbin:/bin:/usr/sbin:/usr/bin'
> SRCTOP='/usr/src'
> OBJTOP='/usr/obj/powerpc64vtsc_clang_altbinutils/powerpc.powerpc64/usr/src/powerpc.powerpc64'
> .MAKE.MAKEFILES='/usr/src/share/mk/sys.mk /usr/src/share/mk/local.sys.env.mk /usr/src/share/mk/src.sys.env.mk /root/src.configs/src.conf.powerpc64-clang_altbinutils-bootstrap.amd64-host /usr/src/share/mk/bsd.mkopt.mk /usr/src/share/mk/src.sys.obj.mk /usr/src/share/mk/auto.obj.mk /usr/src/share/mk/bsd.suffixes.mk /root/src.configs/make.conf /usr/src/share/mk/local.sys.mk /usr/src/share/mk/src.sys.mk /dev/null /usr/src/lib/csu/powerpc64/Makefile /usr/src/share/mk/bsd.lib.mk /usr/src/share/mk/bsd.init.mk /usr/src/share/mk/bsd.opts.mk /usr/src/share/mk/bsd.cpu.mk /usr/src/share/mk/local.init.mk /usr/src/share/mk/src.init.mk /usr/src/lib/csu/powerpc64/../Makefile.inc /usr/src/share/mk/src.opts.mk /usr/src/share/mk/bsd.own.mk /usr/src/share/mk/bsd.compiler.mk /usr/src/share/mk/bsd.linker.mk /usr/src/lib/csu/powerpc64/../../Makefile.inc /usr/src/share/mk/bsd.libnames.mk /usr/src/share/mk/src.libnames.mk /usr/src/share/mk/bsd.symver.mk /usr/src/share/mk/bsd.nls.mk /usr/src/share/mk/bsd.confs.mk /usr/src/share/mk/bsd.files.mk /usr/src/share/mk/bsd.dirs.mk /usr/src/share/mk/bsd.incs.mk /usr/src/share/mk/bsd.links.mk /usr/src/share/mk/bsd.dep.mk /usr/src/share/mk/bsd.clang-analyze.mk /usr/src/share/mk/bsd.obj.mk /usr/src/share/mk/bsd.subdir.mk /usr/src/share/mk/bsd.sys.mk'
> .PATH='. /usr/src/lib/csu/powerpc64 /usr/src/lib/csu/common'
> 1 error
> END QUOTES
>
>
> For (D) (lldb):
>
> QUOTES
> CPU not supported
> UNREACHABLE executed at /usr/src/contrib/llvm/tools/lldb/source/Plugins/Process/FreeBSD/FreeBSDThread.cpp:192!
> Abort trap (core dumped)
>
> (gdb) bt
> #0 0x0000000813715208 in .__sys_thr_kill () at thr_kill.S:3
> #1 0x00000008137147cc in __raise (s=<optimized out>) at /usr/src/lib/libc/gen/raise.c:52
> #2 0x000000081366b5d8 in abort () at /usr/src/lib/libc/stdlib/abort.c:79
> #3 0x0000000011df6fb8 in llvm::llvm_unreachable_internal () at /usr/src/contrib/llvm/lib/Support/ErrorHandling.cpp:222
> #4 0x00000000103aaaf8 in FreeBSDThread::GetRegisterContext () at /usr/src/contrib/llvm/tools/lldb/source/Plugins/Process/FreeBSD/FreeBSDThread.cpp:192
> #5 0x00000000105807d4 in lldb_private::Thread::SetupForResume () at /usr/src/contrib/llvm/tools/lldb/source/Target/Thread.cpp:613
> #6 0x0000000010571bc8 in lldb_private::ThreadList::WillResume () at /usr/src/contrib/llvm/tools/lldb/source/Target/ThreadList.cpp:541
> #7 0x00000000105da23c in lldb_private::Process::PrivateResume () at /usr/src/contrib/llvm/tools/lldb/source/Target/Process.cpp:3281
> #8 0x00000000105a00c8 in lldb_private::Target::Launch () at /usr/src/contrib/llvm/tools/lldb/source/Target/Target.cpp:2922
> #9 0x000000001073f550 in CommandObjectProcessLaunch::DoExecute () at /usr/src/contrib/llvm/tools/lldb/source/Commands/CommandObjectProcess.cpp:221
> #10 0x00000000106c36c4 in lldb_private::CommandObjectParsed::Execute () at /usr/src/contrib/llvm/tools/lldb/source/Interpreter/CommandObject.cpp:975
> #11 0x00000000106d8b44 in lldb_private::CommandInterpreter::HandleCommand () at /usr/src/contrib/llvm/tools/lldb/source/Interpreter/CommandInterpreter.cpp:1761
> #12 0x00000000106da0a0 in lldb_private::CommandInterpreter::IOHandlerInputComplete () at /usr/src/contrib/llvm/tools/lldb/source/Interpreter/CommandInterpreter.cpp:2801
> #13 0x00000000107c0a08 in lldb_private::IOHandlerEditline::Run () at /usr/src/contrib/llvm/tools/lldb/source/Core/IOHandler.cpp:558
> #14 0x0000000010346e5c in lldb_private::Debugger::ExecuteIOHandlers () at /usr/src/contrib/llvm/tools/lldb/source/Core/Debugger.cpp:988
> #15 0x00000000106c8ddc in lldb_private::CommandInterpreter::RunCommandInterpreter () at /usr/src/contrib/llvm/tools/lldb/source/Interpreter/CommandInterpreter.cpp:3003
> #16 0x000000001034feb4 in lldb::SBDebugger::RunCommandInterpreter () at /usr/src/contrib/llvm/tools/lldb/source/API/SBDebugger.cpp:935
> #17 0x00000000101de878 in Driver::MainLoop () at /usr/src/contrib/llvm/tools/lldb/tools/driver/Driver.cpp:756
> #18 0x00000000101a0088 in main () at /usr/src/contrib/llvm/tools/lldb/tools/driver/Driver.cpp:936
>
> lldb::RegisterContextSP FreeBSDThread::GetRegisterContext() {
> if (!m_reg_context_sp) {
> m_posix_thread = nullptr;
>
> RegisterInfoInterface *reg_interface = nullptr;
> const ArchSpec &target_arch = GetProcess()->GetTarget().GetArchitecture();
>
> switch (target_arch.GetMachine()) {
> case llvm::Triple::aarch64:
> reg_interface = new RegisterInfoPOSIX_arm64(target_arch);
> break;
> case llvm::Triple::arm:
> reg_interface = new RegisterInfoPOSIX_arm(target_arch);
> break;
> case llvm::Triple::ppc:
> #ifndef __powerpc64__
> reg_interface = new RegisterContextFreeBSD_powerpc32(target_arch);
> break;
> #endif
> case llvm::Triple::ppc64:
> reg_interface = new RegisterContextFreeBSD_powerpc64(target_arch);
> break;
> case llvm::Triple::mips64:
> reg_interface = new RegisterContextFreeBSD_mips64(target_arch);
> break;
> case llvm::Triple::x86:
> reg_interface = new RegisterContextFreeBSD_i386(target_arch);
> break;
> case llvm::Triple::x86_64:
> reg_interface = new RegisterContextFreeBSD_x86_64(target_arch);
> break;
> default:
> llvm_unreachable("CPU not supported");
> }
> END QUOTES.
I ran into libunwind having LIBUNWIND_PRINT_UNWINDING and
LIBUNWIND_PRINT_APIS so I can report for the segmentation
fault:
# export LIBUNWIND_PRINT_UNWINDING=""
# export LIBUNWIND_PRINT_APIS=""
# ./a.out
libunwind: _Unwind_RaiseException(ex_obj=0x810043060)
libunwind: unw_init_local(cursor=0x3fffffffffffcb68, context=0x3fffffffffffd100)
libunwind: unw_step(cursor=0x3fffffffffffcb68)
libunwind: unw_get_proc_info(cursor=0x3fffffffffffcb68, &info=0x3fffffffffffd850)
libunwind: unw_get_proc_name(cursor=0x3fffffffffffcb68, &buf=0x3fffffffffffd648, bufLen=512)
libunwind: unw_get_reg(cursor=0x3fffffffffffcb68, regNum=-1, &value=0x3fffffffffffd638)
libunwind: unwind_phase1(ex_ojb=0x810043060): pc=0x81019d954, start_ip=0x81019d860, func=.anonymous., lsda=0x0, personality=0x0
libunwind: unw_step(cursor=0x3fffffffffffcb68)
libunwind: unw_get_proc_info(cursor=0x3fffffffffffcb68, &info=0x3fffffffffffd850)
libunwind: unw_get_proc_name(cursor=0x3fffffffffffcb68, &buf=0x3fffffffffffd648, bufLen=512)
libunwind: unw_get_reg(cursor=0x3fffffffffffcb68, regNum=-1, &value=0x3fffffffffffd638)
libunwind: unwind_phase1(ex_ojb=0x810043060): pc=0x10000da8, start_ip=0x10000d64, func=.anonymous., lsda=0x10000f84, personality=0x8101b5360
libunwind: unwind_phase1(ex_ojb=0x810043060): calling personality function 0x8101b5360
libunwind: unw_get_proc_info(cursor=0x3fffffffffffcb68, &info=0x3fffffffffffc970)
libunwind: _Unwind_GetLanguageSpecificData(context=0x3fffffffffffcb68) => 0x10000f84
libunwind: unw_get_proc_info(cursor=0x3fffffffffffcb68, &info=0x3fffffffffffc8b0)
libunwind: _Unwind_GetRegionStart(context=0x3fffffffffffcb68) => 0x10000d64
libunwind: unw_get_reg(cursor=0x3fffffffffffcb68, regNum=-1, &value=0x3fffffffffffc8e8)
libunwind: _Unwind_GetIP(context=0x3fffffffffffcb68) => 0x10000da8
libunwind: unw_get_proc_info(cursor=0x3fffffffffffcb68, &info=0x3fffffffffffc8a0)
libunwind: _Unwind_GetRegionStart(context=0x3fffffffffffcb68) => 0x10000d64
libunwind: unw_get_reg(cursor=0x3fffffffffffcb68, regNum=-2, &value=0x3fffffffffffd848)
libunwind: unwind_phase1(ex_ojb=0x810043060): _URC_HANDLER_FOUND
libunwind: unw_init_local(cursor=0x3fffffffffffcb68, context=0x3fffffffffffd100)
libunwind: unwind_phase2(ex_ojb=0x810043060)
libunwind: unw_step(cursor=0x3fffffffffffcb68)
libunwind: unw_get_reg(cursor=0x3fffffffffffcb68, regNum=-2, &value=0x3fffffffffffca78)
libunwind: unw_get_proc_info(cursor=0x3fffffffffffcb68, &info=0x3fffffffffffca30)
libunwind: unw_get_proc_name(cursor=0x3fffffffffffcb68, &buf=0x3fffffffffffc830, bufLen=512)
libunwind: unwind_phase2(ex_ojb=0x810043060): start_ip=0x81019d860, func=.anonymous., sp=0x3fffffffffffd900, lsda=0x0, personality=0x0
libunwind: unw_step(cursor=0x3fffffffffffcb68)
libunwind: unw_get_reg(cursor=0x3fffffffffffcb68, regNum=-2, &value=0x3fffffffffffca78)
libunwind: unw_get_proc_info(cursor=0x3fffffffffffcb68, &info=0x3fffffffffffca30)
libunwind: unw_get_proc_name(cursor=0x3fffffffffffcb68, &buf=0x3fffffffffffc830, bufLen=512)
libunwind: unwind_phase2(ex_ojb=0x810043060): start_ip=0x10000d64, func=.anonymous., sp=0x3fffffffffffd9a0, lsda=0x10000f84, personality=0x8101b5360
libunwind: unw_get_proc_info(cursor=0x3fffffffffffcb68, &info=0x3fffffffffffc630)
libunwind: _Unwind_GetLanguageSpecificData(context=0x3fffffffffffcb68) => 0x10000f84
libunwind: _Unwind_SetIP(context=0x3fffffffffffcb68, value=0x10000dac)
libunwind: unw_set_reg(cursor=0x3fffffffffffcb68, regNum=-1, value=0x10000dac)
libunwind: _Unwind_SetGR(context=0x3fffffffffffcb68, reg=3, value=0x810043060)
libunwind: unw_set_reg(cursor=0x3fffffffffffcb68, regNum=3, value=0x810043060)
libunwind: _Unwind_SetGR(context=0x3fffffffffffcb68, reg=4, value=0x1)
libunwind: unw_set_reg(cursor=0x3fffffffffffcb68, regNum=4, value=0x1)
libunwind: unwind_phase2(ex_ojb=0x810043060): _URC_INSTALL_CONTEXT
libunwind: unw_get_reg(cursor=0x3fffffffffffcb68, regNum=-1, &value=0x3fffffffffffc830)
libunwind: unw_get_reg(cursor=0x3fffffffffffcb68, regNum=-2, &value=0x3fffffffffffca78)
libunwind: unwind_phase2(ex_ojb=0x810043060): re-entering user code with ip=0x10000dac, sp=0x3fffffffffffd9a0
libunwind: unw_resume(cursor=0x3fffffffffffcb68)
Segmentation fault (core dumped)
Note that the 0x10000dac address below is after the "ld r2,40(r1)"
that sets up r2's value for use in the
00000018.plt_call.__cxa_begin_catch@@CXXABI_1.3 routine. The
ip value reported by unwind_phase2 appears to too large by 0x4 .
(gdb) disass main
Dump of assembler code for function main():
0x0000000010000d64 <+0>: mflr r0
0x0000000010000d68 <+4>: std r31,-8(r1)
0x0000000010000d6c <+8>: std r0,16(r1)
0x0000000010000d70 <+12>: stdu r1,-128(r1)
0x0000000010000d74 <+16>: mr r31,r1
0x0000000010000d78 <+20>: li r3,8
0x0000000010000d7c <+24>: bl 0x100007a0 <00000018.plt_call.__cxa_allocate_exception@@CXXABI_1.3>
0x0000000010000d80 <+28>: ld r2,40(r1)
0x0000000010000d84 <+32>: nop
0x0000000010000d88 <+36>: ld r4,-32728(r2)
0x0000000010000d8c <+40>: addi r4,r4,16
0x0000000010000d90 <+44>: std r4,0(r3)
0x0000000010000d94 <+48>: nop
0x0000000010000d98 <+52>: nop
0x0000000010000d9c <+56>: ld r4,-32720(r2)
0x0000000010000da0 <+60>: ld r5,-32712(r2)
0x0000000010000da4 <+64>: bl 0x10000800 <00000018.plt_call.__cxa_throw@@CXXABI_1.3>
0x0000000010000da8 <+68>: ld r2,40(r1)
0x0000000010000dac <+72>: bl 0x100007c0 <00000018.plt_call.__cxa_begin_catch@@CXXABI_1.3>
0x0000000010000db0 <+76>: ld r2,40(r1)
0x0000000010000db4 <+80>: bl 0x100007e0 <00000018.plt_call.__cxa_end_catch@@CXXABI_1.3>
0x0000000010000db8 <+84>: ld r2,40(r1)
0x0000000010000dbc <+88>: li r3,0
0x0000000010000dc0 <+92>: addi r1,r1,128
0x0000000010000dc4 <+96>: ld r0,16(r1)
0x0000000010000dc8 <+100>: ld r31,-8(r1)
0x0000000010000dcc <+104>: mtlr r0
0x0000000010000dd0 <+108>: blr
0x0000000010000dd4 <+112>: .long 0x0
0x0000000010000dd8 <+116>: .long 0x0
0x0000000010000ddc <+120>: .long 0x0
End of assembler dump.
===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)
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