Quick top note: clang 5 does generate code sequences with AltiVec stvx and lvx instructions where r97-r108 are listed but powerpc64-gcc is not doing so in those same sorts of places. This appears to be a ABI variation across toolchains to me, unless such is fully optional in the ABI somehow.
On 2017-Oct-8, at 6:34 AM, Mark Millard <markmi at dsl-only.net> wrote: > [Looks like r97-r108 are for vr20-vr31 (AltiVec > Registers).] > > On 2017-Oct-8, at 4:34 AM, Mark Millard <markmi at dsl-only.net> wrote: > >> From a dwarfdump's _Unwind_RaiseException information >> from a clang/clang++ 5 based compile: >> >> 91 DW_CFA_offset_extended r97 -496 (62 * -8) >> 94 DW_CFA_offset_extended r98 -480 (60 * -8) >> 97 DW_CFA_offset_extended r99 -464 (58 * -8) >> 100 DW_CFA_offset_extended r100 -448 (56 * -8) >> 103 DW_CFA_offset_extended r101 -432 (54 * -8) >> 106 DW_CFA_offset_extended r102 -416 (52 * -8) >> 109 DW_CFA_offset_extended r103 -400 (50 * -8) >> 112 DW_CFA_offset_extended r104 -384 (48 * -8) >> 115 DW_CFA_offset_extended r105 -368 (46 * -8) >> 118 DW_CFA_offset_extended r106 -352 (44 * -8) >> 121 DW_CFA_offset_extended r107 -336 (42 * -8) >> 124 DW_CFA_offset_extended r108 -320 (40 * -8) >> >> By contrast devel/powerpc64-gcc does not produce any >> of those. Is this lack of support of some part of an >> ABI? Is clang going outside the range of the intended >> ABI? > > ABI64BitOpenPOWERv1.1_16July2015_pub.pdf indicates > that r97-r108 are for vr20-vr31 (AltiVec Registers). > [Is AltiVec optional --possibly missing?] > > So the questions translate into questions about > AltiVec support/handling for C++ exceptions. > > [Note: R70 is supposed to be specific to CR2.] > >> Does FreeBSD's libgcc_s design and implementation handle >> these additional logical registers? > . . . > > So the libgcc_s question traces back to: does it > handle AltiVec Registers vr20-vr31 if they are > referenced (clang)? Is it well behaved if r97-r108 > are not referenced (powerpc64-gcc)? > >> Supporting notes: >> >> r46-r63 are for floating point registers (that >> have been around for a long time: older >> powerpc family members). > > r46-r63 are for f14-f31. > >> r70 is for having/using the value from "mfcr". > > Apparently r70 is supposed to be specific to CR2. > >> r2(?)-r6 are scratch for C++ exception handling. >> (I originally identified r3-r6. r2 might have a >> somewhat distinct status?) > > In normal functions r2-r6 do not get > DW_CFA_offset_extended_sf or > DW_CFA_offset entries. They are special > to some internal exception handling > routines. (See later.) > >> r14-r31 are for the normal r14 through r31 >> registers. > > r97-r108 are for AltiVec Registers vr20-vr31. > >> r65 is standard and heavily used on all(?) >> routines, not just some libgcc_s ones. (So >> r65 is not listed below.) > > r65 for lr. > >> In libgcc_s.so.1.full (via powerpc64-gcc): >> >> uw_update_context_1: r70 >> _Unwind_RaiseException: r[2-6],r4[6-9],r5[0-9],r6[0-3],r70 >> _Unwind_RaiseException_Phase2: (nothing special matched) >> _Unwind_ForcedUnwind: r[2-6],r4[6-9],r5[0-9],r6[0-3],r70 >> _Unwind_Resume: r[2-6],r4[6-9],r5[0-9],r6[0-3],r70 >> _Unwind_Resume_or_Rethrow: r[2-6],r4[6-9],r5[0-9],r6[0-3],r70 >> _Unwind_Backtrace: r4[6-9],r5[0-9],r6[0-3],r70 >> __deregister_frame_info_bases: r70 >> _Unwind_Find_FDE: r70 > > So no AltiVec Registers listed. > >> In libgcc_s.so.1.full (via clang): >> >> uw_update_context_1: r70 (uw_update_context_1 was actually later >> in the file) >> _Unwind_RaiseException: r4[6-9],r5[0-9],r6[0-3],r70,r9[7-9],r10[0-8] >> _Unwind_RaiseException_Phase2: r70 >> _Unwind_ForcedUnwind: r4[6-9],r5[0-9],r6[0-3],r70,r9[7-9],r10[0-8] >> _Unwind_Resume: r4[6-9],r5[0-9],r6[0-3],r70,r9[7-9],r10[0-8] >> _Unwind_Resume_or_Rethrow: r4[6-9],r5[0-9],r6[0-3],r70,r9[7-9],r10[0-8] >> _Unwind_Backtrace: r4[6-9],r5[0-9],r6[0-3],r70,r9[7-9],r10[0-8] >> __deregister_frame_info_bases: (nothing special matched) >> _Unwind_Find_FDE: (nothing special matched) > > So no internal, special-for-excpetion-routines > scratch register usage listed (r2-r6). > >> clang is missing all the r[2-6] references but >> the code generated does have the registers in >> use. Thrown C++ exceptions crash because of >> the lack of the r2-r6's, dying on a r3 attempt. >> > . . . >> >> I have no clue why _Unwind_RaiseException_Phase2 >> has a r70 for clang but not for powerpc64-gcc. >> Or the other way around for __deregister_frame_info_bases >> and _Unwind_Find_FDE. >> >> Which file's implementations are used from >> what I can tell : >> >> uw_update_context_1: /usr/src/contrib/gcc/unwind-dw2.c >> _Unwind_RaiseException: /usr/src/contrib/gcc/unwind.inc >> _Unwind_RaiseException_Phase2: /usr/src/contrib/gcc/unwind.inc >> _Unwind_ForcedUnwind: /usr/src/contrib/gcc/unwind.inc >> _Unwind_Resume: /usr/src/contrib/gcc/unwind.inc >> _Unwind_Resume_or_Rethrow: /usr/src/contrib/gcc/unwind.inc >> _Unwind_Backtrace: /usr/src/contrib/gcc/unwind.inc >> __deregister_frame_info_bases: /usr/src/contrib/gcc/unwind-dw2-fde.c >> _Unwind_Find_FDE: /usr/src/contrib/gcc/unwind-dw2-fde*.c >> (unsure) >> >> An implication is that GPL Version 2 source code >> is involved even when clang is the system compiler. >> Is that what FreeBSD intends for the powerpc >> families? >> >> /* Exception handling and frame unwind runtime interface routines. -*- C -*- >> Copyright (C) 2001, 2003 Free Software Foundation, Inc. >> >> This file is part of GCC. >> >> GCC is free software; you can redistribute it and/or modify it >> under the terms of the GNU General Public License as published by >> the Free Software Foundation; either version 2, or (at your option) >> any later version. >> >> In addition to the permissions in the GNU General Public License, the >> Free Software Foundation gives you unlimited permission to link the >> compiled version of this file into combinations with other programs, >> and to distribute those combinations without any restriction coming >> from the use of this file. (The General Public License restrictions >> do apply in other respects; for example, they cover modification of >> the file, and distribution when not linked into a combined >> executable.) >> >> . . . >> >> Does libgcc_s.so.1 with its type of use form a "combined executable"? === Mark Millard markmi at dsl-only.net _______________________________________________ freebsd-toolchain@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-toolchain To unsubscribe, send any mail to "freebsd-toolchain-unsubscr...@freebsd.org"
