Re: [PATCH v2] elf: Remove -fno-tree-loop-distribute-patterns usage on dl-support

["H.J. Lu" <hjl.tools@gmail.com>]

On Wed, Aug 10, 2022 at 11:58 AM Adhemerval Zanella Netto
<adhemerval.zanella@linaro.org> wrote:
>
>
>
> On 10/08/22 14:24, H.J. Lu wrote:
> > On Wed, Aug 10, 2022 at 8:40 AM Adhemerval Zanella
> > <adhemerval.zanella@linaro.org> wrote:
> >>
> >> Besides the option being gcc specific, this approach is still fragile
> >> and not future proof since we do not if this will be the only
> >> optimization option gcc will add that transform loops to memset
> >> (or any libcall).
> >>
> >> This patch add a new header dl-symbol-hacks.h that can be used to
> >> redirect the compiler generated libcalls to port specific string
> >> implementatation if required (defined by dl-ifunc-generic.h).
> >>
> >> Checked on x86_64-linux-gnu and aarch64-linux-gnu.
> >> ---
> >>  elf/Makefile                                  |  5 ---
> >>  elf/dl-support.c                              |  1 +
> >>  elf/dl-symbol-hacks.h                         | 31 ++++++++++++++++
> >>  elf/dl-tunables.c                             |  1 +
> >>  sysdeps/generic/dl-ifunc-generic.h            | 37 +++++++++++++++++++
> >>  .../sysv/linux/aarch64/dl-ifunc-generic.h     | 24 ++++++++++++
> >>  .../unix/sysv/linux/i386/dl-ifunc-generic.h   | 26 +++++++++++++
> >>  .../sysv/linux/powerpc/dl-ifunc-generic.h     | 28 ++++++++++++++
> >>  .../unix/sysv/linux/s390/dl-ifunc-generic.h   | 31 ++++++++++++++++
> >>  .../unix/sysv/linux/sparc/dl-ifunc-generic.h  | 26 +++++++++++++
> >>  .../unix/sysv/linux/x86_64/dl-ifunc-generic.h | 32 ++++++++++++++++
> >>  11 files changed, 237 insertions(+), 5 deletions(-)
> >>  create mode 100644 elf/dl-symbol-hacks.h
> >>  create mode 100644 sysdeps/generic/dl-ifunc-generic.h
> >>  create mode 100644 sysdeps/unix/sysv/linux/aarch64/dl-ifunc-generic.h
> >>  create mode 100644 sysdeps/unix/sysv/linux/i386/dl-ifunc-generic.h
> >>  create mode 100644 sysdeps/unix/sysv/linux/powerpc/dl-ifunc-generic.h
> >>  create mode 100644 sysdeps/unix/sysv/linux/s390/dl-ifunc-generic.h
> >>  create mode 100644 sysdeps/unix/sysv/linux/sparc/dl-ifunc-generic.h
> >>  create mode 100644 sysdeps/unix/sysv/linux/x86_64/dl-ifunc-generic.h
> >>
> >> diff --git a/elf/Makefile b/elf/Makefile
> >> index 3386f0ce77..4b992bd348 100644
> >> --- a/elf/Makefile
> >> +++ b/elf/Makefile
> >> @@ -162,11 +162,6 @@ ifeq (yes,$(have-loop-to-function))
> >>  CFLAGS-rtld.c += -fno-tree-loop-distribute-patterns
> >>  endif
> >>
> >> -ifeq (yes,$(have-loop-to-function))
> >> -# Likewise, during static library startup, memset is not yet available.
> >> -CFLAGS-dl-support.c = -fno-tree-loop-distribute-patterns
> >> -endif
> >> -
> >>  # Compile rtld itself without stack protection.
> >>  # Also compile all routines in the static library that are elided from
> >>  # the shared libc because they are in libc.a in the same way.
> >> diff --git a/elf/dl-support.c b/elf/dl-support.c
> >> index 4af0b5b2ce..6d1996ae6e 100644
> >> --- a/elf/dl-support.c
> >> +++ b/elf/dl-support.c
> >> @@ -44,6 +44,7 @@
> >>  #include <dl-auxv.h>
> >>  #include <dl-find_object.h>
> >>  #include <array_length.h>
> >> +#include <dl-symbol-hacks.h>
> >>
> >>  extern char *__progname;
> >>  char **_dl_argv = &__progname; /* This is checked for some error messages.  */
> >> diff --git a/elf/dl-symbol-hacks.h b/elf/dl-symbol-hacks.h
> >> new file mode 100644
> >> index 0000000000..6b9d24ed03
> >> --- /dev/null
> >> +++ b/elf/dl-symbol-hacks.h
> >> @@ -0,0 +1,31 @@
> >> +/* Symbol rediretion for loader/static initialization code.
> >> +   Copyright (C) 2022 Free Software Foundation, Inc.
> >> +   This file is part of the GNU C Library.
> >> +
> >> +   The GNU C Library is free software; you can redistribute it and/or
> >> +   modify it under the terms of the GNU Lesser General Public
> >> +   License as published by the Free Software Foundation; either
> >> +   version 2.1 of the License, or (at your option) any later version.
> >> +
> >> +   The GNU C Library 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
> >> +   Lesser General Public License for more details.
> >> +
> >> +   You should have received a copy of the GNU Lesser General Public
> >> +   License along with the GNU C Library; if not, see
> >> +   <https://www.gnu.org/licenses/>.  */
> >> +
> >> +#ifndef _DL_SYMBOL_HACKS_H
> >> +#define _DL_SYMBOL_HACKS_H
> >> +
> >> +#include <dl-ifunc-generic.h>
> >> +
> >> +/* Some compiler optimizations may transform loops into memset/memmove
> >> +   calls and without proper redirection it might call PLT throught
> >> +   ifunc without relocations being processed.  */
> >> +#if !IS_IN(rtld) && defined HAVE_MEMSET_IFUNC_GENERIC
> >> +asm ("memset = " HAVE_MEMSET_IFUNC_GENERIC);
> >> +#endif
> >> +
> >> +#endif
> >> diff --git a/elf/dl-tunables.c b/elf/dl-tunables.c
> >> index 8e7ee9df10..c797484522 100644
> >> --- a/elf/dl-tunables.c
> >> +++ b/elf/dl-tunables.c
> >> @@ -32,6 +32,7 @@
> >>  #include <ldsodefs.h>
> >>  #include <array_length.h>
> >>  #include <dl-minimal-malloc.h>
> >> +#include <dl-symbol-hacks.h>
> >>
> >>  #define TUNABLES_INTERNAL 1
> >>  #include "dl-tunables.h"
> >> diff --git a/sysdeps/generic/dl-ifunc-generic.h b/sysdeps/generic/dl-ifunc-generic.h
> >> new file mode 100644
> >> index 0000000000..5e1d5c1fd8
> >> --- /dev/null
> >> +++ b/sysdeps/generic/dl-ifunc-generic.h
> >> @@ -0,0 +1,37 @@
> >> +/* Symbol rediretion for loader/static initialization code.
> >> +   Copyright (C) 2022 Free Software Foundation, Inc.
> >> +   This file is part of the GNU C Library.
> >> +
> >> +   The GNU C Library is free software; you can redistribute it and/or
> >> +   modify it under the terms of the GNU Lesser General Public
> >> +   License as published by the Free Software Foundation; either
> >> +   version 2.1 of the License, or (at your option) any later version.
> >> +
> >> +   The GNU C Library 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
> >> +   Lesser General Public License for more details.
> >> +
> >> +   You should have received a copy of the GNU Lesser General Public
> >> +   License along with the GNU C Library; if not, see
> >> +   <https://www.gnu.org/licenses/>.  */
> >> +
> >> +#ifndef _DL_IFUNC_GENERIC_H
> >> +#define _DL_IFUNC_GENERIC_H
> >> +
> >> +/* The compiler might optimize loops or other constructs to library calls even
> >> +   in freestanding mode.  Although it is safe in most scenarios, on program
> >> +   loading and static startup, iFUNC resolution might require other dynamic
> >> +   relocation that are not yet done.
> >> +
> >> +   Instead of adding per-file compiler flags to avoid the libcall generation,
> >> +   this header defines generic symbols that will be routed instead of the
> >> +   default symbols name.
> >> +
> >> +   Each port can then define the following macro to the expected generic
> >> +   implementation if the symbol is provided as iFUNC:
> >> +
> >> +   HAVE_MEMSET_IFUNC_GENERIC - the generic memset call.
> >> + */
> >> +
> >> +#endif
> >> diff --git a/sysdeps/unix/sysv/linux/aarch64/dl-ifunc-generic.h b/sysdeps/unix/sysv/linux/aarch64/dl-ifunc-generic.h
> >> new file mode 100644
> >> index 0000000000..1278a06ff0
> >> --- /dev/null
> >> +++ b/sysdeps/unix/sysv/linux/aarch64/dl-ifunc-generic.h
> >> @@ -0,0 +1,24 @@
> >> +/* Symbol rediretion for loader/static initialization code.
> >> +   Copyright (C) 2022 Free Software Foundation, Inc.
> >> +   This file is part of the GNU C Library.
> >> +
> >> +   The GNU C Library is free software; you can redistribute it and/or
> >> +   modify it under the terms of the GNU Lesser General Public
> >> +   License as published by the Free Software Foundation; either
> >> +   version 2.1 of the License, or (at your option) any later version.
> >> +
> >> +   The GNU C Library 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
> >> +   Lesser General Public License for more details.
> >> +
> >> +   You should have received a copy of the GNU Lesser General Public
> >> +   License along with the GNU C Library; if not, see
> >> +   <https://www.gnu.org/licenses/>.  */
> >> +
> >> +#ifndef _DL_IFUNC_GENERIC_H
> >> +#define _DL_IFUNC_GENERIC_H
> >> +
> >> +#define HAVE_MEMSET_IFUNC_GENERIC "__memset_generic"
> >> +
> >> +#endif
> >> diff --git a/sysdeps/unix/sysv/linux/i386/dl-ifunc-generic.h b/sysdeps/unix/sysv/linux/i386/dl-ifunc-generic.h
> >> new file mode 100644
> >> index 0000000000..c8e294b3c9
> >> --- /dev/null
> >> +++ b/sysdeps/unix/sysv/linux/i386/dl-ifunc-generic.h
> >> @@ -0,0 +1,26 @@
> >> +/* Symbol rediretion for loader/static initialization code.
> >> +   Copyright (C) 2022 Free Software Foundation, Inc.
> >> +   This file is part of the GNU C Library.
> >> +
> >> +   The GNU C Library is free software; you can redistribute it and/or
> >> +   modify it under the terms of the GNU Lesser General Public
> >> +   License as published by the Free Software Foundation; either
> >> +   version 2.1 of the License, or (at your option) any later version.
> >> +
> >> +   The GNU C Library 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
> >> +   Lesser General Public License for more details.
> >> +
> >> +   You should have received a copy of the GNU Lesser General Public
> >> +   License along with the GNU C Library; if not, see
> >> +   <https://www.gnu.org/licenses/>.  */
> >> +
> >> +#ifndef _DL_IFUNC_GENERIC_H
> >> +#define _DL_IFUNC_GENERIC_H
> >> +
> >> +#ifdef USE_MULTIARCH
> >> +# define HAVE_MEMSET_IFUNC_GENERIC "__memset_ia32"
> >> +#endif
> >> +
> >> +#endif
> >
> > This file should be in sysdeps/i386/i686/multiarch.
> >
>
> My understanding is we only support iFUNC for Linux, but it seems that multiarch
> directory is not Linux specific. I will change it.
>
> >> diff --git a/sysdeps/unix/sysv/linux/powerpc/dl-ifunc-generic.h b/sysdeps/unix/sysv/linux/powerpc/dl-ifunc-generic.h
> >> new file mode 100644
> >> index 0000000000..b0f9401670
> >> --- /dev/null
> >> +++ b/sysdeps/unix/sysv/linux/powerpc/dl-ifunc-generic.h
> >> @@ -0,0 +1,28 @@
> >> +/* Symbol rediretion for loader/static initialization code.
> >> +   Copyright (C) 2022 Free Software Foundation, Inc.
> >> +   This file is part of the GNU C Library.
> >> +
> >> +   The GNU C Library is free software; you can redistribute it and/or
> >> +   modify it under the terms of the GNU Lesser General Public
> >> +   License as published by the Free Software Foundation; either
> >> +   version 2.1 of the License, or (at your option) any later version.
> >> +
> >> +   The GNU C Library 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
> >> +   Lesser General Public License for more details.
> >> +
> >> +   You should have received a copy of the GNU Lesser General Public
> >> +   License along with the GNU C Library; if not, see
> >> +   <https://www.gnu.org/licenses/>.  */
> >> +
> >> +#ifndef _DL_IFUNC_GENERIC_H
> >> +#define _DL_IFUNC_GENERIC_H
> >> +
> >> +/* powerpc and powerpc64 provides the default memset as 'memset', so
> >> +   no need to redirect it.  */
> >> +#if defined USE_MULTIARCH && defined __powerpc64__  && _CALL_ELF != 2
> >> +# define HAVE_MEMSET_IFUNC_GENERIC "__memset_power8"
> >> +#endif
> >> +
> >> +#endif
> >> diff --git a/sysdeps/unix/sysv/linux/s390/dl-ifunc-generic.h b/sysdeps/unix/sysv/linux/s390/dl-ifunc-generic.h
> >> new file mode 100644
> >> index 0000000000..f664ac07a7
> >> --- /dev/null
> >> +++ b/sysdeps/unix/sysv/linux/s390/dl-ifunc-generic.h
> >> @@ -0,0 +1,31 @@
> >> +/* Symbol rediretion for loader/static initialization code.
> >> +   Copyright (C) 2022 Free Software Foundation, Inc.
> >> +   This file is part of the GNU C Library.
> >> +
> >> +   The GNU C Library is free software; you can redistribute it and/or
> >> +   modify it under the terms of the GNU Lesser General Public
> >> +   License as published by the Free Software Foundation; either
> >> +   version 2.1 of the License, or (at your option) any later version.
> >> +
> >> +   The GNU C Library 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
> >> +   Lesser General Public License for more details.
> >> +
> >> +   You should have received a copy of the GNU Lesser General Public
> >> +   License along with the GNU C Library; if not, see
> >> +   <https://www.gnu.org/licenses/>.  */
> >> +
> >> +#ifndef _DL_IFUNC_GENERIC_H
> >> +#define _DL_IFUNC_GENERIC_H
> >> +
> >> +#ifdef USE_MULTIARCH
> >> +# include <ifunc-memset.h>
> >> +
> >> +# define IFUNC_SYMBOL_STR1(s)  #s
> >> +# define IFUNC_SYMBOL_STR(s)   IFUNC_SYMBOL_STR1(s)
> >> +
> >> +# define HAVE_MEMSET_IFUNC_GENERIC IFUNC_SYMBOL_STR(MEMSET_DEFAULT)
> >> +#endif
> >> +
> >> +#endif
> >> diff --git a/sysdeps/unix/sysv/linux/sparc/dl-ifunc-generic.h b/sysdeps/unix/sysv/linux/sparc/dl-ifunc-generic.h
> >> new file mode 100644
> >> index 0000000000..86815317a9
> >> --- /dev/null
> >> +++ b/sysdeps/unix/sysv/linux/sparc/dl-ifunc-generic.h
> >> @@ -0,0 +1,26 @@
> >> +/* Symbol rediretion for loader/static initialization code.
> >> +   Copyright (C) 2022 Free Software Foundation, Inc.
> >> +   This file is part of the GNU C Library.
> >> +
> >> +   The GNU C Library is free software; you can redistribute it and/or
> >> +   modify it under the terms of the GNU Lesser General Public
> >> +   License as published by the Free Software Foundation; either
> >> +   version 2.1 of the License, or (at your option) any later version.
> >> +
> >> +   The GNU C Library 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
> >> +   Lesser General Public License for more details.
> >> +
> >> +   You should have received a copy of the GNU Lesser General Public
> >> +   License along with the GNU C Library; if not, see
> >> +   <https://www.gnu.org/licenses/>.  */
> >> +
> >> +#ifndef _DL_IFUNC_GENERIC_H
> >> +#define _DL_IFUNC_GENERIC_H
> >> +
> >> +#ifdef USE_MULTIARCH
> >> +# define HAVE_MEMSET_IFUNC_GENERIC "__memset_ultra1"
> >> +#endif
> >> +
> >> +#endif
> >> diff --git a/sysdeps/unix/sysv/linux/x86_64/dl-ifunc-generic.h b/sysdeps/unix/sysv/linux/x86_64/dl-ifunc-generic.h
> >> new file mode 100644
> >> index 0000000000..7b7cf1c3d6
> >> --- /dev/null
> >> +++ b/sysdeps/unix/sysv/linux/x86_64/dl-ifunc-generic.h
> >> @@ -0,0 +1,32 @@
> >> +/* Symbol rediretion for loader/static initialization code.
> >> +   Copyright (C) 2022 Free Software Foundation, Inc.
> >> +   This file is part of the GNU C Library.
> >> +
> >> +   The GNU C Library is free software; you can redistribute it and/or
> >> +   modify it under the terms of the GNU Lesser General Public
> >> +   License as published by the Free Software Foundation; either
> >> +   version 2.1 of the License, or (at your option) any later version.
> >> +
> >> +   The GNU C Library 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
> >> +   Lesser General Public License for more details.
> >> +
> >> +   You should have received a copy of the GNU Lesser General Public
> >> +   License along with the GNU C Library; if not, see
> >> +   <https://www.gnu.org/licenses/>.  */
> >> +
> >> +#ifndef _DL_IFUNC_GENERIC_H
> >> +#define _DL_IFUNC_GENERIC_H
> >> +
> >> +#include <isa-level.h>
> >> +
> >> +#if MINIMUM_X86_ISA_LEVEL >= 4
> >> +# define HAVE_MEMSET_IFUNC_GENERIC "__memset_evex_unaligned"
> >> +#elif MINIMUM_X86_ISA_LEVEL == 3
> >> +# define HAVE_MEMSET_IFUNC_GENERIC "__memset_avx2_unaligned"
> >> +#else
> >> +# define HAVE_MEMSET_IFUNC_GENERIC "__memset_sse2_unaligned"
> >> +#endif
> >> +
> >> +#endif
> >> --
> >> 2.34.1
> >>
> >
> > This file should be in sysdeps/x86_64/multiarch and the generic
> > memset should follow sysdeps/x86_64/memset.S:
> >
> > #define DEFAULT_IMPL_V1 "multiarch/memset-sse2-unaligned-erms.S"
> > #define DEFAULT_IMPL_V3 "multiarch/memset-avx2-unaligned-erms.S"
> > #define DEFAULT_IMPL_V4 "multiarch/memset-evex-unaligned-erms.S"
>
> Right, my understading it does follow the provided implementation based
> on the MINIMUM_X86_ISA_LEVEL.  What I am missing here?

You are right.  The file content is OK.  But it should be in
sysdeps/x86_64/multiarch.

-- 
H.J.