NetBSD Problem Report #55837

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Date: Wed,  2 Dec 2020 08:59:40 +0000 (UTC)
From: rokuyama.rk@gmail.com
Reply-To: rokuyama.rk@gmail.com
To: gnats-bugs@NetBSD.org
Subject: GCC 9.3 g++ generates wrong codes for hard-float arm
X-Send-Pr-Version: www-1.0

>Number:         55837
>Category:       toolchain
>Synopsis:       GCC 9.3 g++ generates wrong codes for hard-float arm
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    toolchain-manager
>State:          closed
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Dec 02 09:00:00 +0000 2020
>Closed-Date:    Mon May 31 12:16:49 +0000 2021
>Last-Modified:  Mon May 31 22:35:01 +0000 2021
>Originator:     Rin Okuyama
>Release:        7.99.76
>Organization:
Department of Physics, Meiji University
>Environment:
NetBSD rpi0w 9.99.76 NetBSD 9.99.76 (RPI0EB) #12: Tue Dec  1 11:02:35 JST 2020  rin@latipes:/build/work/src/sys/arch/evbarm/compile/RPI0EB evbarm
>Description:
g++ from GCC 9.3 generates wrong codes for hard-float arm variants, i.e.,
earmv[5-7]hf{,eb}. The situation is much more serious on v[5-6]hf{eb},
but v7hf{,eb} is also affected. On the other hand, soft-float variants,
earmv[4-7] seem not affected as far as I can see.

For GDB on v[5-6]hf, trying to place breakpoint on non-existent symbol
causes abort:

on v7hf{,eb}:

|(gdb) b non_existent_symbol
|Function "non_existent_symbol" not defined.
|Make breakpoint pending on future shared library load? (y or [n])

on v[5-6]hf{,eb}:

|(gdb) b non_existent_symbol
|terminate called after throwing an instance of 'gdb_exception_RETURN_MASK_ERROR'
|[1]   Abort trap (core dumped) gdb ./hello

Or backtrace longer than one display screen cannot quit by ``q'':

on v7hf{,eb}:

|(gdb) bt
|...
|--Type <RET> for more, q to quit, c to continue without paging--q
|Quit
|(gdb)

on v[5-6]hf{,eb}:

|(gdb) bt
|...
|--Type <RET> for more, q to quit, c to continue without paging--q
|terminate called after throwing an instance of 'gdb_exception_RETURN_MASK_QUIT'
|[1]   Abort trap (core dumped) gdb atf-run atf-run.core

Note that even v7hf{,eb} is affected; we already works around similar
failure in exception handling on v7hf{,eb}. See doc/HACKS:

	https://nxr.netbsd.org/xref/src/doc/HACKS#978

or toolchain/54820:

	http://gnats.netbsd.org/54820

The failures do not occur on soft-float arm variants as far as I can see.

On hard-float arm variants, if whole GDB is compiled with -O0, they do not
occur. Alternatively, compiling GDB by GCC 8.4 remarkably mitigates the
problems, although GCC8 is not perfect; hack described above was initially
introduced for GCC8.

Even if the other parts of userland, shared-libs, rtld, etc., are compiled
by GCC8, the problems occur when GDB itself is compiled by GCC9.

For ATF on v[5-6]hf{,eb}, atf-run aborts like:

on v[5-6]hf{,eb}

| # atf-run | atf-report
| ...
| atf-c/detail/fs_test (3/68): 24 test cases
|    eaccess: [0.021425s] Passed.
|    exists: terminate called after throwing an instance of 'tools::parser::parse_error'
|  what():  LONELY PARSE ERROR: 237: Unexpected token `<<EOF>>'; expected end of
|test case or test case's stdout/stderr line
|[1]   Segmentation fault (core dumped) atf-run |
|      Abort trap (core dumped) atf-report
| #

Many tests in /usr/tests/atf fail due to ``Failed: Test program received
signal 6 (core dumped)''.

These failures do not occur on soft-float variants. If all source codes of
ATF are compiled with -O0, these do not occur also.
>How-To-Repeat:
On earmv[5-6]hf{,eb} machines,

# gdb hello
...
(gdb) b non-existent-symbol

or

# cd /usr/tests/atf && atf-run | atf-report

The problems also occurs for COMPAT_NETBSD32 on aarch64{,eb}.
>Fix:
Exception handling is suspicious, but I haven't still figured out what
actually happens. Note that while other OS's use arm specific exception
handling, NetBSD uses normal DWARF exception handling based on libunwind.

>Release-Note:

>Audit-Trail:
From: Rin Okuyama <rokuyama.rk@gmail.com>
To: "gnats-bugs@NetBSD.org" <gnats-bugs@NetBSD.org>
Cc: 
Subject: Re: toolchain/55837 (GCC 9.3 g++ generates wrong codes for hard-float
 arm)
Date: Fri, 30 Apr 2021 21:29:36 +0900

 I tried to compile sys/lib/libunwind with VFP instructions being disabled
 forcibly with this patch:

 http://www.netbsd.org/~rin/arm_unwind_20210430.patch

 But the situation does not change unfortunately...

 Note that patch for GCC is necessary because -mgeneral-regs-only does not
 work for some C++ headers like:

 ----
 /build/gcc9/dest/evbarm-earmv6hfeb/usr/include/g++/bits/std_abs.h: In function 'constexpr double std::abs(double)':
 /build/gcc9/dest/evbarm-earmv6hfeb/usr/include/g++/bits/std_abs.h:71:17: error: argument of type 'double' not permitted with -mgeneral-regs-only
     71 |   abs(double __x)
 ----

 We may need more -mgeneral-regs-only for libstdc++, c.f.:

 ---
 % find /usr/src/external/gpl3/gcc/dist/libstdc++-v3 -name '*.cc' | \
 xargs grep general-regs-only
 /usr/src/external/gpl3/gcc/dist/libstdc++-v3/libsupc++/eh_personality.cc:__attribute__((target ("general-regs-only")))
 /usr/src/external/gpl3/gcc/dist/libstdc++-v3/libsupc++/eh_personality.cc:__attribute__((target ("general-regs-only")))
 ---

 Thanks,
 rin

From: Rin Okuyama <rokuyama.rk@gmail.com>
To: "gnats-bugs@NetBSD.org" <gnats-bugs@NetBSD.org>
Cc: 
Subject: Re: toolchain/55837 (GCC 9.3 g++ generates wrong codes for hard-float
 arm)
Date: Mon, 31 May 2021 20:33:02 +0900

 It turned out that this is not due to bugs in GCC, but in
 libunwind for arm. I will commit fixes soon.

 Thanks,
 rin

From: "Rin Okuyama" <rin@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/55837 CVS commit: src/sys/lib/libunwind
Date: Mon, 31 May 2021 11:41:22 +0000

 Module Name:	src
 Committed By:	rin
 Date:		Mon May 31 11:41:22 UTC 2021

 Modified Files:
 	src/sys/lib/libunwind: Registers.hpp unwind_registers.S

 Log Message:
 PR toolchain/55837

 Misc style fixes for clarity:

 - Rename lazyVFP1() and lazyVFP3() to lazyVFPv2() and lazyVFPv3(),
   respectively. Note that VFPv1 was obsoleted and replaced by VFPv2.

 - Introduce enum for flags.

 - Add few comments.

 No functional changes.


 To generate a diff of this commit:
 cvs rdiff -u -r1.21 -r1.22 src/sys/lib/libunwind/Registers.hpp
 cvs rdiff -u -r1.18 -r1.19 src/sys/lib/libunwind/unwind_registers.S

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

From: "Rin Okuyama" <rin@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/55837 CVS commit: src/sys/lib/libunwind
Date: Mon, 31 May 2021 11:44:07 +0000

 Module Name:	src
 Committed By:	rin
 Date:		Mon May 31 11:44:07 UTC 2021

 Modified Files:
 	src/sys/lib/libunwind: Registers.hpp

 Log Message:
 PR toolchain/55837

 copyFloatVectorRegister(): Assert register number is valid to make sure.


 To generate a diff of this commit:
 cvs rdiff -u -r1.22 -r1.23 src/sys/lib/libunwind/Registers.hpp

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

From: "Rin Okuyama" <rin@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/55837 CVS commit: src/sys/lib/libunwind
Date: Mon, 31 May 2021 11:47:18 +0000

 Module Name:	src
 Committed By:	rin
 Date:		Mon May 31 11:47:18 UTC 2021

 Modified Files:
 	src/sys/lib/libunwind: unwind_registers.S

 Log Message:
 PR toolchain/55837

 Fix for jumpto() armeb; use word-wise load for flags, instead of byte-wise one.


 To generate a diff of this commit:
 cvs rdiff -u -r1.19 -r1.20 src/sys/lib/libunwind/unwind_registers.S

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

From: "Rin Okuyama" <rin@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/55837 CVS commit: src/sys/lib/libunwind
Date: Mon, 31 May 2021 11:50:43 +0000

 Module Name:	src
 Committed By:	rin
 Date:		Mon May 31 11:50:43 UTC 2021

 Modified Files:
 	src/sys/lib/libunwind: Registers.hpp

 Log Message:
 PR toolchain/55837

 Fix DWARF/internal register numbers of s31 for arm.


 To generate a diff of this commit:
 cvs rdiff -u -r1.23 -r1.24 src/sys/lib/libunwind/Registers.hpp

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

From: "Rin Okuyama" <rin@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/55837 CVS commit: src/sys/lib/libunwind
Date: Mon, 31 May 2021 11:54:01 +0000

 Module Name:	src
 Committed By:	rin
 Date:		Mon May 31 11:54:01 UTC 2021

 Modified Files:
 	src/sys/lib/libunwind: Registers.hpp

 Log Message:
 PR toolchain/55837

 Fix pointer arithmetic when copying s0-s31 registers for arm.


 To generate a diff of this commit:
 cvs rdiff -u -r1.24 -r1.25 src/sys/lib/libunwind/Registers.hpp

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

From: "Rin Okuyama" <rin@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/55837 CVS commit: src/sys/lib/libunwind
Date: Mon, 31 May 2021 11:57:28 +0000

 Module Name:	src
 Committed By:	rin
 Date:		Mon May 31 11:57:28 UTC 2021

 Modified Files:
 	src/sys/lib/libunwind: Registers.hpp

 Log Message:
 PR toolchain/55837

 Fix logic error in copyFloatVectorRegister() for arm; copy s0-s31 or
 d0-d31, not both.


 To generate a diff of this commit:
 cvs rdiff -u -r1.25 -r1.26 src/sys/lib/libunwind/Registers.hpp

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

From: "Rin Okuyama" <rin@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/55837 CVS commit: src/sys/lib/libunwind
Date: Mon, 31 May 2021 12:12:24 +0000

 Module Name:	src
 Committed By:	rin
 Date:		Mon May 31 12:12:24 UTC 2021

 Modified Files:
 	src/sys/lib/libunwind: Registers.hpp

 Log Message:
 PR toolchain/55837

 Bump LAST_REGISTER and LAST_RESTORE_REG to REGNO_ARM32_S31 for arm.

 There are two numbering schemes for VFPv2 registers: s0-s31 and d0-d15.
 The former is used by GCC, and the latter is by LLVM. Since libunwind was
 derived from LLVM, it has never supported the former. This results in
 crashes for GCC-compiled binaries in exception handler of C++, if it
 encounters VFPv2 registers when unwinding frames.

 This commit adds support for s0-s31 numbering to libunwind. I choose an
 implementation in which VFPv2 registers are ``double-counted'' as s0-s31
 AND d0-d15. This does not cause real problems, since the former is only
 used by GCC, and the later is by LLVM. That is, different numbering
 schemes cannot appear in a same frame. To make sure, assertions are added
 in order to check this.

 I've confirmed that no regression for ATF both for GCC- and LLVM-compiled
 userlands.


 To generate a diff of this commit:
 cvs rdiff -u -r1.26 -r1.27 src/sys/lib/libunwind/Registers.hpp

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

State-Changed-From-To: open->closed
State-Changed-By: rin@NetBSD.org
State-Changed-When: Mon, 31 May 2021 12:16:49 +0000
State-Changed-Why:
Fixes for libunwind were committed.


From: "Rin Okuyama" <rin@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/55837 CVS commit: src/sys/lib/libunwind
Date: Mon, 31 May 2021 21:31:34 +0000

 Module Name:	src
 Committed By:	rin
 Date:		Mon May 31 21:31:34 UTC 2021

 Modified Files:
 	src/sys/lib/libunwind: Registers.hpp

 Log Message:
 PR toolchain/55837

 Stop using enum for flags, as per request from joerg.

 #define constants and #undef after use.


 To generate a diff of this commit:
 cvs rdiff -u -r1.27 -r1.28 src/sys/lib/libunwind/Registers.hpp

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

From: "Rin Okuyama" <rin@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/55837 CVS commit: src
Date: Mon, 31 May 2021 22:33:19 +0000

 Module Name:	src
 Committed By:	rin
 Date:		Mon May 31 22:33:19 UTC 2021

 Modified Files:
 	src/doc: HACKS
 	src/external/gpl3/gdb.old/lib/libgdb: Makefile
 	src/external/gpl3/gdb/lib/libgdb: Makefile

 Log Message:
 PR toolchain/55837

 Get rid of -O0 hack for GDB for hard-float arm. This was necessary because
 libunwind did not support s0-s31. Note that for *most* cases (not all!),
 -O0 stops using VFP registers for general purposes.

 Also note that this hack was incomplete. We had to compile every functions
 with -O0, that can be unwinded. Otherwise, GDB crashed every time exceptions
 were raised.


 To generate a diff of this commit:
 cvs rdiff -u -r1.217 -r1.218 src/doc/HACKS
 cvs rdiff -u -r1.12 -r1.13 src/external/gpl3/gdb.old/lib/libgdb/Makefile
 cvs rdiff -u -r1.30 -r1.31 src/external/gpl3/gdb/lib/libgdb/Makefile

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

>Unformatted:

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