Date: Thu, 25 Feb 2016 00:56:23 +0000 From: bugzilla-noreply@freebsd.org To: freebsd-bugs@FreeBSD.org Subject: [Bug 207359] projects/clang380-import for TARGET_ARCH=powerpc64 via powerpc64-gcc : c++ exceptions unbounded loop in _Unwind_RaiseException (9 line program) Message-ID: <bug-207359-8-Uacbi9tKNY@https.bugs.freebsd.org/bugzilla/> In-Reply-To: <bug-207359-8@https.bugs.freebsd.org/bugzilla/> References: <bug-207359-8@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D207359 --- Comment #2 from Mark Millard <markmi@dsl-only.net> --- I've finally traced the low level details of the _Unwind_RaiseException stu= ck looping failure. . . Starting from the observed low-level evidence based on observation via gdb = and such: A backtrace while stopped during the unbounded looping is: #0 uw_update_context (context=3Dcontext@entry=3D0xffffffffffffccf0, fs=3Dfs@entry=3D0xffffffffffffc370) at /usr/src/gnu/lib/libgcc/../../../contrib/gcc/unwind-dw2.c:1371 #1 0x00000000501cb95c in _Unwind_RaiseException (exc=3D0x50815058) at /usr/src/gnu/lib/libgcc/../../../contrib/gcc/unwind.inc:126 #2 0x000000005016e3a0 in throw_exception (ex=3D0x50815000) at /usr/src/lib/libcxxrt/../../contrib/libcxxrt/exception.cc:751 #3 0x0000000010000d50 in main () at exception_test.cpp:5 _Unwind_RaiseException never returns for source code that looks like: #include <exception> int main(void) { try { throw std::exception(); } catch (std::exception& e) {} return 0; } where in /usr/lib/libc++.so.1 there is: 736 static void throw_exception(__cxa_exception *ex) 737 { . . . 751 _Unwind_Reason_Code err =3D _Unwind_RaiseException(&ex->unwindHeader); . . . 756 } The unbounded loop in _Unwind_RaiseException is in the code: 85 _Unwind_Reason_Code 86 _Unwind_RaiseException(struct _Unwind_Exception *exc) 87 { 88 struct _Unwind_Context this_context, cur_context; 89 _Unwind_Reason_Code code; 90=20=20=20=20=20=20 91 /* Set up this_context to describe the current stack frame. */ 92 uw_init_context (&this_context); 93 cur_context =3D this_context; 94=20=20=20=20=20=20 95 /* Phase 1: Search. Unwind the stack, calling the personality routine 96 with the _UA_SEARCH_PHASE flag set. Do not modify the stack y= et.=20 */ 97 while (1) 98 { 99 _Unwind_FrameState fs; 100=20=20=20=20=20 101 /* Set up fs to describe the FDE for the caller of cur_contex= t.=20 The 102 first time through the loop, that means __cxa_throw. */ 103 code =3D uw_frame_state_for (&cur_context, &fs); . . . 125 /* Update cur_context to describe the same frame as fs. */ 126 uw_update_context (&cur_context, &fs); 127 } . . . 140 } The uw_update_context call is doing the following before returning: 1367 /* Compute the return address now, since the return address column 1368 can change from frame to frame. */ 1369 context->ra =3D __builtin_extract_return_addr 1370 (_Unwind_GetPtr (context, fs->retaddr_column)); with context->ra before and after the call both being 0x5016e3a0 . In fact = it was 0x5016e3a0 for the prior uw_frame_state_for call as well and continues = to be so each loop iteration once the problem starts. As for the code around 0x5016e3a0: 0x5016e398 <throw_exception(__cxxabiv1::__cxa_exception*)+136>: stw= =20=20=20=20 r10,48(r9) 0x5016e39c <throw_exception(__cxxabiv1::__cxa_exception*)+140>: bl= =20=20=20=20=20 0x50162ae0 <00000017.plt_call._Unwind_RaiseException@@GCC_3.0> 0x5016e3a0 <throw_exception(__cxxabiv1::__cxa_exception*)+144>: ld= =20=20=20=20=20 r2,40(r1) 0x5016e3a4 <throw_exception(__cxxabiv1::__cxa_exception*)+148>: add= i=20=20=20 r1,r1,128 0x5016e3a8 <throw_exception(__cxxabiv1::__cxa_exception*)+152>: mr= =20=20=20=20=20 r4,r31 0x5016e3ac <throw_exception(__cxxabiv1::__cxa_exception*)+156>: ld= =20=20=20=20=20 r0,16(r1) From /usr/local/bin/objdump for FreeBSD projects/clang380-import -r295902's /usr/lib/libc++.so.1 for the same code (to match up with the .eh_frame dwarf information presented later): 0000000000015398 <.__cxa_end_catch+0x4d8> stw r10,48(r9) 000000000001539c <.__cxa_end_catch+0x4dc> bl 0000000000009ae0 <CXXABI_1.3+0x9ae0> 00000000000153a0 <.__cxa_end_catch+0x4e0> ld r2,40(r1) 00000000000153a4 <.__cxa_end_catch+0x4e4> addi r1,r1,128 00000000000153a8 <.__cxa_end_catch+0x4e8> mr r4,r31 00000000000153ac <.__cxa_end_catch+0x4ec> ld r0,16(r1) The code block above from 153a0 up to 153a8 is being given 153a0 as its "re= turn address" (context->ra) by uw_update_context via interpreting the dwarf .eh_frame information. So once in that range there it never leaves that ran= ge. The relevant dwarfdump output spanning that area is: (Note that 153a0 up to 153a8 is part of the range that includes the bl to _Unwind_RaiseException .) < 0><0x00015310:0x000153dc><><fde offset 0x000010d8 length: 0x00000034><= eh aug data len 0x0> 0x00015310: <off cfa=3D00(r1) >=20 0x00015318: <off cfa=3D00(r1) > <off r31=3D-8(cfa) > <off r65=3Dr0 = >=20 0x00015324: <off cfa=3D128(r1) > <off r31=3D-8(cfa) > <off r65=3D16= (cfa) >=20 0x00015368: <off cfa=3D00(r1) > <off r31=3D-8(cfa) > <off r65=3D16(= cfa) >=20 0x00015378: <off cfa=3D00(r1) >=20 0x00015380: <off cfa=3D128(r1) > <off r31=3D-8(cfa) > <off r65=3D16= (cfa) >=20 0x000153a8: <off cfa=3D00(r1) > <off r31=3D-8(cfa) > <off r65=3D16(= cfa) >=20 0x000153b8: <off cfa=3D00(r1) >=20 0x000153c0: <off cfa=3D128(r1) > <off r31=3D-8(cfa) > <off r65=3D16= (cfa) >=20 fde section offset 4312 0x000010d8 cie offset for fde: 4316 0x000010dc 0 DW_CFA_advance_loc 8 (2 * 4) 1 DW_CFA_register r65 =3D r0 4 DW_CFA_offset r31 -8 (1 * -8) 6 DW_CFA_advance_loc 12 (3 * 4) 7 DW_CFA_def_cfa_offset 128 10 DW_CFA_offset_extended_sf r65 16 (-2 * -8) 13 DW_CFA_advance_loc 68 (17 * 4) 14 DW_CFA_remember_state 15 DW_CFA_def_cfa_offset 0 17 DW_CFA_advance_loc 16 (4 * 4) 18 DW_CFA_restore_extended r65 20 DW_CFA_restore r31 21 DW_CFA_advance_loc 8 (2 * 4) 22 DW_CFA_restore_state 23 DW_CFA_advance_loc 40 (10 * 4) 24 DW_CFA_remember_state 25 DW_CFA_def_cfa_offset 0 27 DW_CFA_advance_loc 16 (4 * 4) 28 DW_CFA_restore_extended r65 30 DW_CFA_restore r31 31 DW_CFA_advance_loc 8 (2 * 4) 32 DW_CFA_restore_state 33 DW_CFA_nop 34 DW_CFA_nop 35 DW_CFA_nop 36 DW_CFA_nop 37 DW_CFA_nop 38 DW_CFA_nop Note that the stack pointer manipulation (incrementing/popping) *after* the return from the bl. 15339c, 153a0, and 153a4 should be 3 distinct contexts = in the .eh_frame information but are not: 000000000001539c <.__cxa_end_catch+0x4dc> bl 0000000000009ae0 <CXXABI_1.3+0x9ae0> 00000000000153a0 <.__cxa_end_catch+0x4e0> ld r2,40(r1) 00000000000153a4 <.__cxa_end_catch+0x4e4> addi r1,r1,128 So there is a missing step or more of frame-context tracking in the .eh_fra= me information. --=20 You are receiving this mail because: You are the assignee for the bug.=
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