Re: [PATCH v4] elf: Remove -fno-tree-loop-distribute-patterns usage on dl-support

[Carlos O'Donell <carlos@redhat.com>]

On Thu, Aug 11, 2022 at 09:19:09AM -0300, Adhemerval Zanella via Libc-alpha 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

s/do not/do not know/g

> optimization option gcc will add that transform loops to memset

s/transform/transforms/g

> (or any libcall).
> 
> This patch add a new header dl-symbol-hacks.h that can be used to

s/add/adds/g
s/dl-symbol-hacks.h/, dl-symbol-hacks.h,/g

> 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 ++++++++++++++++
>  sysdeps/aarch64/multiarch/dl-ifunc-generic.h  | 24 ++++++++++++
>  sysdeps/generic/dl-ifunc-generic.h            | 37 +++++++++++++++++++
>  .../i386/i686/multiarch/dl-ifunc-generic.h    | 24 ++++++++++++
>  .../powerpc64/le/multiarch/dl-ifunc-generic.h | 24 ++++++++++++
>  sysdeps/s390/multiarch/dl-ifunc-generic.h     | 29 +++++++++++++++
>  .../sparcv9/multiarch/dl-ifunc-generic.h      | 24 ++++++++++++
>  .../sparc64/multiarch/dl-ifunc-generic.h      | 24 ++++++++++++
>  sysdeps/x86_64/multiarch/dl-ifunc-generic.h   | 32 ++++++++++++++++
>  11 files changed, 250 insertions(+), 5 deletions(-)
>  create mode 100644 elf/dl-symbol-hacks.h
>  create mode 100644 sysdeps/aarch64/multiarch/dl-ifunc-generic.h
>  create mode 100644 sysdeps/generic/dl-ifunc-generic.h
>  create mode 100644 sysdeps/i386/i686/multiarch/dl-ifunc-generic.h
>  create mode 100644 sysdeps/powerpc/powerpc64/le/multiarch/dl-ifunc-generic.h
>  create mode 100644 sysdeps/s390/multiarch/dl-ifunc-generic.h
>  create mode 100644 sysdeps/sparc/sparc32/sparcv9/multiarch/dl-ifunc-generic.h
>  create mode 100644 sysdeps/sparc/sparc64/multiarch/dl-ifunc-generic.h
>  create mode 100644 sysdeps/x86_64/multiarch/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
> -

OK.

>  # 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>

OK.

>  
>  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..1b83b284dd
> --- /dev/null
> +++ b/elf/dl-symbol-hacks.h

Bikeshed. Call it "dl-symbol-redir.h" since that's what it does.

Can we get rid of this?

Can we flatten the headers out?

At the very least I think we want to remove the typo-prone macro
API and always define the macros.

> @@ -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

s/PLT throught/through the PLT via an/g

> +   ifunc without relocations being processed.  */
> +#ifdef HAVE_MEMSET_IFUNC_GENERIC

Typo unsafe macro API.

Can we always define this? Use a generic definition?

> +asm ("memset = " HAVE_MEMSET_IFUNC_GENERIC);
> +#endif
> +
> +#endif
> diff --git a/sysdeps/aarch64/multiarch/dl-ifunc-generic.h b/sysdeps/aarch64/multiarch/dl-ifunc-generic.h
> new file mode 100644
> index 0000000000..1278a06ff0
> --- /dev/null
> +++ b/sysdeps/aarch64/multiarch/dl-ifunc-generic.h

Call it "dl-symbol-redir-ifunc.h"?

This is not generic, it is aarch64 specific.

> @@ -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/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

Call it "dl-symbol-redir-ifunc.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.
> + */
> +

Define the macro by default.

> +#endif
> diff --git a/sysdeps/i386/i686/multiarch/dl-ifunc-generic.h b/sysdeps/i386/i686/multiarch/dl-ifunc-generic.h
> new file mode 100644
> index 0000000000..a538931c03
> --- /dev/null
> +++ b/sysdeps/i386/i686/multiarch/dl-ifunc-generic.h

Call it "dl-symbol-redir-ifunc.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_ia32"

OK.

> +
> +#endif
> diff --git a/sysdeps/powerpc/powerpc64/le/multiarch/dl-ifunc-generic.h b/sysdeps/powerpc/powerpc64/le/multiarch/dl-ifunc-generic.h
> new file mode 100644
> index 0000000000..1bf516494d
> --- /dev/null
> +++ b/sysdeps/powerpc/powerpc64/le/multiarch/dl-ifunc-generic.h

Call it "dl-symbol-redir-ifunc.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_power8"

OK.

> +
> +#endif
> diff --git a/sysdeps/s390/multiarch/dl-ifunc-generic.h b/sysdeps/s390/multiarch/dl-ifunc-generic.h
> new file mode 100644
> index 0000000000..b0e5ed23aa
> --- /dev/null
> +++ b/sysdeps/s390/multiarch/dl-ifunc-generic.h

Call it "dl-symbol-redir-ifunc.h"?

> @@ -0,0 +1,29 @@
> +/* 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 <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)

OK. Ugh.

> +
> +#endif
> diff --git a/sysdeps/sparc/sparc32/sparcv9/multiarch/dl-ifunc-generic.h b/sysdeps/sparc/sparc32/sparcv9/multiarch/dl-ifunc-generic.h
> new file mode 100644
> index 0000000000..417b24d2c1
> --- /dev/null
> +++ b/sysdeps/sparc/sparc32/sparcv9/multiarch/dl-ifunc-generic.h

Call it "dl-symbol-redir-ifunc.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_ultra1"

OK.

> +
> +#endif
> diff --git a/sysdeps/sparc/sparc64/multiarch/dl-ifunc-generic.h b/sysdeps/sparc/sparc64/multiarch/dl-ifunc-generic.h
> new file mode 100644
> index 0000000000..417b24d2c1
> --- /dev/null
> +++ b/sysdeps/sparc/sparc64/multiarch/dl-ifunc-generic.h

Call it "dl-symbol-redir-ifunc.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_ultra1"

OK.

> +
> +#endif
> diff --git a/sysdeps/x86_64/multiarch/dl-ifunc-generic.h b/sysdeps/x86_64/multiarch/dl-ifunc-generic.h
> new file mode 100644
> index 0000000000..7b7cf1c3d6
> --- /dev/null
> +++ b/sysdeps/x86_64/multiarch/dl-ifunc-generic.h

Call it "dl-symbol-redir-ifunc.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

OK.

> +
> +#endif
> -- 
> 2.34.1
>