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

Adhemerval Zanella Netto adhemerval.zanella@linaro.org
Wed Aug 10 18:58:44 GMT 2022



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?


More information about the Libc-alpha mailing list