Introduce <gmon-entry.h> to define TEXT_START for csu/gmon-start.c

  The generic version uses <entry.h> to obtain the ENTRY_POINT
name and redeclares it as a data symbol, under a different
identifier.  This way, it is no longer necessary to inhibit the
declaration of the entry point as a function.

The previous approach to define __ASSEMBLY__ to suppress the
declaration breaks if headers included by <entry.h> are not
compatible with __ASSEMBLY__.  This happens with rseq integration
because it is necessary to include kernel headers in more places.

Tested on i686-linux-gnu and x86_64-linux-gnu.  Built with
build-many-glibcs.py.

---
 csu/gmon-start.c                                   | 22 ++---------------
 sysdeps/generic/gmon-entry.h                       | 28 ++++++++++++++++++++++
 sysdeps/hppa/{entry.h => gmon-entry.h}             |  9 ++-----
 sysdeps/ia64/entry.h                               | 13 ----------
 sysdeps/ia64/gmon-entry.h                          |  7 ++++++
 .../powerpc/powerpc64/{entry.h => gmon-entry.h}    | 23 +++++++-----------
 6 files changed, 47 insertions(+), 55 deletions(-)
  

On Sat, Dec 4, 2021 at 12:36 PM Florian Weimer via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> The generic version uses <entry.h> to obtain the ENTRY_POINT
> name and redeclares it as a data symbol, under a different
> identifier.  This way, it is no longer necessary to inhibit the
> declaration of the entry point as a function.
>
> The previous approach to define __ASSEMBLY__ to suppress the
> declaration breaks if headers included by <entry.h> are not
> compatible with __ASSEMBLY__.  This happens with rseq integration
> because it is necessary to include kernel headers in more places.
>
> Tested on i686-linux-gnu and x86_64-linux-gnu.  Built with
> build-many-glibcs.py.
>
> ---
>  csu/gmon-start.c                                   | 22 ++---------------
>  sysdeps/generic/gmon-entry.h                       | 28 ++++++++++++++++++++++
>  sysdeps/hppa/{entry.h => gmon-entry.h}             |  9 ++-----
>  sysdeps/ia64/entry.h                               | 13 ----------
>  sysdeps/ia64/gmon-entry.h                          |  7 ++++++
>  .../powerpc/powerpc64/{entry.h => gmon-entry.h}    | 23 +++++++-----------
>  6 files changed, 47 insertions(+), 55 deletions(-)
>
> diff --git a/csu/gmon-start.c b/csu/gmon-start.c
> index 344606a676..1e35e2f829 100644
> --- a/csu/gmon-start.c
> +++ b/csu/gmon-start.c
> @@ -38,32 +38,14 @@
>  #include <stdlib.h>
>  #include <unistd.h>
>  #include <elf-initfini.h>
> -#define __ASSEMBLY__
> -#include <entry.h>
> -
> -/* Beginning and end of our code segment. We cannot declare them
> -   as the external functions since we want the addresses of those
> -   labels. Taking the address of a function may have different
> -   meanings on different platforms. */
> -#ifdef ENTRY_POINT_DECL
> -ENTRY_POINT_DECL(extern)
> -#else
> -extern char ENTRY_POINT[];
> -#endif
> -extern char etext[];
> +#include <gmon-entry.h>
>
>  /* Use __executable_start as the lowest address to keep profiling records
>     if it provided by the linker.  */
>  extern const char executable_start[] asm ("__executable_start")
>    __attribute__ ((weak, visibility ("hidden")));
>
> -#ifndef TEXT_START
> -# ifdef ENTRY_POINT_DECL
> -#  define TEXT_START ENTRY_POINT
> -# else
> -#  define TEXT_START &ENTRY_POINT
> -# endif
> -#endif
> +extern char etext[];

Can we drop TEXT_START and always use __executable_start?

commit 84a7eb1f87c1d01b58ad887a0ab5d87abbc1c772
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Fri Jul 30 19:07:30 2021 -0700

    Use __executable_start as the lowest address for profiling [BZ #28153]

    Glibc assumes that ENTRY_POINT is the lowest address for which we need
    to keep profiling records and BFD linker uses a linker script to place
    the input sections.

    Starting from GCC 4.6, the main function is placed in .text.startup
    section and starting from binutils 2.22, BFD linker with

    commit add44f8d5c5c05e08b11e033127a744d61c26aee
    Author: Alan Modra <amodra@gmail.com>
    Date:   Thu Nov 25 03:03:02 2010 +0000

                * scripttempl/elf.sc: Group .text.exit, text.startup
and .text.hot
                sections.

    places .text.startup section before .text section, which leave the main
    function out of profiling records.

    Starting from binutils 2.15, linker provides __executable_start to mark
    the lowest address of the executable.  Use __executable_start as the
    lowest address to keep the main function in profiling records. This fixes
    [BZ #28153].

>  #if !ELF_INITFINI
>  /* Instead of defining __gmon_start__ globally in gcrt1.o, we make it
> diff --git a/sysdeps/generic/gmon-entry.h b/sysdeps/generic/gmon-entry.h
> new file mode 100644
> index 0000000000..720b0d3338
> --- /dev/null
> +++ b/sysdeps/generic/gmon-entry.h
> @@ -0,0 +1,28 @@
> +/* Entry point address for csu/gmon-start.c.  Generic version.
> +   Copyright (C) 2021 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/>.  */
> +
> +#include <entry.h>
> +
> +/* Beginning and end of our code segment. We cannot declare them
> +   as the external functions since we want the addresses of those
> +   labels. Taking the address of a function may have different
> +   meanings on different platforms. */
> +#define __TEXT_START0(name) \
> +  ({ extern char _start_as_data[] asm (#name); &_start_as_data[0]; })
> +#define __TEXT_START1(name) __TEXT_START0(name)
> +#define TEXT_START __TEXT_START1(ENTRY_POINT)
> diff --git a/sysdeps/hppa/entry.h b/sysdeps/hppa/gmon-entry.h
> similarity index 52%
> rename from sysdeps/hppa/entry.h
> rename to sysdeps/hppa/gmon-entry.h
> index 5ea5b47448..d59f331889 100644
> --- a/sysdeps/hppa/entry.h
> +++ b/sysdeps/hppa/gmon-entry.h
> @@ -1,13 +1,8 @@
> -#ifndef __ASSEMBLY__
> -extern void _start (void);
> -#endif
> +#include <entry.h>
>
>  /* Lives in libgcc.so and canonicalizes function pointers for comparison.  */
>  extern unsigned int __canonicalize_funcptr_for_compare (unsigned int fptr);
>
>  /* The function's entry point is stored in the first word of the
>     function descriptor (plabel) of _start().  */
> -#define ENTRY_POINT __canonicalize_funcptr_for_compare((unsigned int)_start)
> -
> -/* We have to provide a special declaration.  */
> -#define ENTRY_POINT_DECL(class) class void _start (void);
> +#define TEXT_START __canonicalize_funcptr_for_compare((unsigned int)_start)
> diff --git a/sysdeps/ia64/entry.h b/sysdeps/ia64/entry.h
> deleted file mode 100644
> index e11b49fc53..0000000000
> --- a/sysdeps/ia64/entry.h
> +++ /dev/null
> @@ -1,13 +0,0 @@
> -#include <link.h>
> -#include <dl-fptr.h>
> -
> -#ifndef __ASSEMBLY__
> -extern void _start (void);
> -#endif
> -
> -/* The function's entry point is stored in the first word of the
> -   function descriptor (plabel) of _start().  */
> -#define ENTRY_POINT ELF_PTR_TO_FDESC (_start)->ip
> -
> -/* We have to provide a special declaration.  */
> -#define ENTRY_POINT_DECL(class) class void _start (void);
> diff --git a/sysdeps/ia64/gmon-entry.h b/sysdeps/ia64/gmon-entry.h
> new file mode 100644
> index 0000000000..971da7ebd9
> --- /dev/null
> +++ b/sysdeps/ia64/gmon-entry.h
> @@ -0,0 +1,7 @@
> +#include <entry.h>
> +#include <link.h>
> +#include <dl-fptr.h>
> +
> +/* The function's entry point is stored in the first word of the
> +   function descriptor (plabel) of _start().  */
> +#define TEXT_START ELF_PTR_TO_FDESC (_start)->ip
> diff --git a/sysdeps/powerpc/powerpc64/entry.h b/sysdeps/powerpc/powerpc64/gmon-entry.h
> similarity index 73%
> rename from sysdeps/powerpc/powerpc64/entry.h
> rename to sysdeps/powerpc/powerpc64/gmon-entry.h
> index 99c81cb982..04dbfd1231 100644
> --- a/sysdeps/powerpc/powerpc64/entry.h
> +++ b/sysdeps/powerpc/powerpc64/gmon-entry.h
> @@ -1,5 +1,5 @@
> -/* Finding the entry point and start of text.  PowerPC64 version.
> -   Copyright (C) 2002-2021 Free Software Foundation, Inc.
> +/* Entry point address for csu/gmon-start.c.  powerpc64 version.
> +   Copyright (C) 2021 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
> @@ -16,22 +16,15 @@
>     License along with the GNU C Library; if not, see
>     <https://www.gnu.org/licenses/>.  */
>
> -
> -#ifndef __ASSEMBLY__
> -extern void _start (void);
> -#endif
> -
> -#define ENTRY_POINT _start
> -
> -#if _CALL_ELF != 2
> -/* We have to provide a special declaration.  */
> -#define ENTRY_POINT_DECL(class) class void _start (void);
> -
> +#if _CALL_ELF == 2
> +# include <sysdeps/generic/gmon-entry.h>
> +#else
> +# include <entry.h>
>  /* Use the address of ._start as the lowest address for which we need
>     to keep profiling records.  We can't copy the ia64 scheme as our
>     entry poiny address is really the address of the function
>     descriptor, not the actual function entry.  */
> -#define TEXT_START \
> +# define TEXT_START \
>    ({ extern unsigned long int _start_as_data[] asm ("_start");  \
> -     _start_as_data[0]; })
> +    _start_as_data[0]; })
>  #endif
>
  

* H. J. Lu:

> Can we drop TEXT_START and always use __executable_start?

Why wasn' this part

> commit 84a7eb1f87c1d01b58ad887a0ab5d87abbc1c772
> Author: H.J. Lu <hjl.tools@gmail.com>
> Date:   Fri Jul 30 19:07:30 2021 -0700
>
>     Use __executable_start as the lowest address for profiling [BZ #28153]

of this commit?

I want to make a conservative change here.

Thanks,
Florian
  

On Sat, Dec 4, 2021 at 1:14 PM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu:
>
> > Can we drop TEXT_START and always use __executable_start?
>
> Why wasn' this part
>
> > commit 84a7eb1f87c1d01b58ad887a0ab5d87abbc1c772
> > Author: H.J. Lu <hjl.tools@gmail.com>
> > Date:   Fri Jul 30 19:07:30 2021 -0700
> >
> >     Use __executable_start as the lowest address for profiling [BZ #28153]
>
> of this commit?
>
> I want to make a conservative change here.
>

Using TEXT_START as the lowest address has been wrong for more than 10
years.  We should drop it now.
  

* H. J. Lu via Libc-alpha:

> On Sat, Dec 4, 2021 at 1:14 PM Florian Weimer <fweimer@redhat.com> wrote:
>>
>> * H. J. Lu:
>>
>> > Can we drop TEXT_START and always use __executable_start?
>>
>> Why wasn' this part
>>
>> > commit 84a7eb1f87c1d01b58ad887a0ab5d87abbc1c772
>> > Author: H.J. Lu <hjl.tools@gmail.com>
>> > Date:   Fri Jul 30 19:07:30 2021 -0700
>> >
>> >     Use __executable_start as the lowest address for profiling [BZ #28153]
>>
>> of this commit?
>>
>> I want to make a conservative change here.
>>
>
> Using TEXT_START as the lowest address has been wrong for more than 10
> years.  We should drop it now.

It seems to work.  I'm going to run a few mor tests.

Thanks,
Florian