Re: [PATCH][gdb/testsuite] Fix gdb.opt/clobbered-registers-O2.exp with clang

[Luis Machado via Gdb-patches <gdb-patches@sourceware.org>]

On 5/24/22 15:07, Tom de Vries via Gdb-patches wrote:
> Hi,
> 
> When running test-case gdb.opt/clobbered-registers-O2.exp with clang 12.0.1, I
> get:
> ...
> (gdb) run ^M
> Starting program: clobbered-registers-O2 ^M
> ^M
> Program received signal SIGSEGV, Segmentation fault.^M
> gen_movsd (operand0=<optimized out>, operand1=<optimized out>) at \
>    clobbered-registers-O2.c:31^M
> 31              return *start_sequence(operand0, operand1);^M
> (gdb) FAIL: gdb.opt/clobbered-registers-O2.exp: runto: run to start_sequence
> ...
> 
> The problem is that the breakpoint in start_sequence doesn't trigger, because:
> - the call to start_sequence in gen_movsd is optimized away, despite the
>    __attribute__((noinline)), so the actual function start_sequence doesn't get
>    called, and
> - the debug info doesn't contain inlined function info, so there's only one
>    breakpoint location.
> 
> Adding noclone and noipa alongside the noinline attribute doesn't fix this.
> 
> Adding the clang-specific attribute optnone in start_sequence does, but since
> it inhibits all optimization, that's not a preferred solution in a gdb.opt
> test-case, and it would work only for clang and not other compilers that
> possibly have the same issue.
> 
> Fix this by moving functions start_sequence and gen_movsd into their own
> files, as a way of trying harder to enforce noinline/noipa/noclone.
> 
> Tested on x86_64-linux.
> 
> Any comments?
> 
> Thanks,
> - Tom
> 
> [gdb/testsuite] Fix gdb.opt/clobbered-registers-O2.exp with clang
> 
> ---
>   gdb/testsuite/gdb.opt/clobbered-registers-O2-2.c | 24 ++++++++++++++++++++++++
>   gdb/testsuite/gdb.opt/clobbered-registers-O2-3.c | 22 ++++++++++++++++++++++
>   gdb/testsuite/gdb.opt/clobbered-registers-O2.c   | 16 +---------------
>   gdb/testsuite/gdb.opt/clobbered-registers-O2.exp |  5 +++--
>   4 files changed, 50 insertions(+), 17 deletions(-)
> 
> diff --git a/gdb/testsuite/gdb.opt/clobbered-registers-O2-2.c b/gdb/testsuite/gdb.opt/clobbered-registers-O2-2.c
> new file mode 100644
> index 00000000000..c709c043677
> --- /dev/null
> +++ b/gdb/testsuite/gdb.opt/clobbered-registers-O2-2.c
> @@ -0,0 +1,24 @@
> +/* This file is part of GDB, the GNU debugger.
> +
> +   Copyright 2007-2022 Free Software Foundation, Inc.
> +
> +   This program 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 3 of the License, or
> +   (at your option) any later version.
> +
> +   This program is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +   GNU General Public License for more details.
> +
> +   You should have received a copy of the GNU General Public License
> +   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
> +
> +extern unsigned *start_sequence (unsigned *x, unsigned *y);
> +
> +unsigned
> +gen_movsd (unsigned *operand0, unsigned *operand1)
> +{
> +  return *start_sequence (operand0, operand1);
> +}
> diff --git a/gdb/testsuite/gdb.opt/clobbered-registers-O2-3.c b/gdb/testsuite/gdb.opt/clobbered-registers-O2-3.c
> new file mode 100644
> index 00000000000..664d5f20d24
> --- /dev/null
> +++ b/gdb/testsuite/gdb.opt/clobbered-registers-O2-3.c
> @@ -0,0 +1,22 @@
> +/* This file is part of GDB, the GNU debugger.
> +
> +   Copyright 2007-2022 Free Software Foundation, Inc.
> +
> +   This program 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 3 of the License, or
> +   (at your option) any later version.
> +
> +   This program is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +   GNU General Public License for more details.
> +
> +   You should have received a copy of the GNU General Public License
> +   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
> +
> +unsigned *
> +start_sequence (unsigned *x, unsigned *y)
> +{
> +  return (unsigned *)0xdeadbeef;
> +}
> diff --git a/gdb/testsuite/gdb.opt/clobbered-registers-O2.c b/gdb/testsuite/gdb.opt/clobbered-registers-O2.c
> index 83cf2267d1e..8201d99763f 100644
> --- a/gdb/testsuite/gdb.opt/clobbered-registers-O2.c
> +++ b/gdb/testsuite/gdb.opt/clobbered-registers-O2.c
> @@ -15,21 +15,7 @@
>      You should have received a copy of the GNU General Public License
>      along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
>   
> -#ifndef __GNUC__
> -#define __attribute__(x)
> -#endif
> -
> -unsigned * __attribute__((noinline))
> -start_sequence (unsigned * x, unsigned * y)
> -{
> -	return (unsigned *)0xdeadbeef;
> -};
> -
> -unsigned __attribute__((noinline))
> -gen_movsd (unsigned * operand0, unsigned * operand1)
> -{
> -	return *start_sequence(operand0, operand1);
> -}
> +extern unsigned gen_movsd (unsigned *operand0, unsigned *operand1);
>   
>   int main(void)
>   {
> diff --git a/gdb/testsuite/gdb.opt/clobbered-registers-O2.exp b/gdb/testsuite/gdb.opt/clobbered-registers-O2.exp
> index e01f445688d..b38f3642840 100644
> --- a/gdb/testsuite/gdb.opt/clobbered-registers-O2.exp
> +++ b/gdb/testsuite/gdb.opt/clobbered-registers-O2.exp
> @@ -18,7 +18,7 @@
>   # Test displaying call clobbered registers in optimized binaries.
>   # GDB should not show incorrect values.
>   
> -standard_testfile
> +standard_testfile .c -2.c -3.c
>   
>   # What compiler are we using?
>   #
> @@ -26,7 +26,8 @@ if [get_compiler_info] {
>       return -1
>   }
>   
> -if {[prepare_for_testing "failed to prepare" $testfile $srcfile \
> +if {[prepare_for_testing "failed to prepare" $testfile \
> +	 [list $srcfile $srcfile2 $srcfile3] \
>   	 {debug optimize=-O2 nowarnings}]} {
>       return -1
>   }

As mentioned in the other thread, this test can be a bit fragile. If the above works for clang, I'm fine with it.

Thanks for getting this addressed.