[v2] csu: Always use __executable_start in gmon-start.c

  Current binutils defines __executable_start as the lowest text
address, so using the entry point address as a fallback is no
longer necessary.  As a result, overriding <entry.h> is only
necessary if the entry point is not called _start.

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, powerpc-linux-gnu, powerpc64-linux-gnu,
powerpc64le-linux-gnu, x86_64-linux-gnu.  Built with
build-many-glibcs.py.

---
v2: Remove TEXT_START instead of generalizing it.

 csu/gmon-start.c                  | 29 +++--------------------------
 sysdeps/hppa/entry.h              | 13 -------------
 sysdeps/ia64/entry.h              | 13 -------------
 sysdeps/powerpc/powerpc64/entry.h | 37 -------------------------------------
 4 files changed, 3 insertions(+), 89 deletions(-)
  

On Sun, Dec 5, 2021 at 2:37 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> Current binutils defines __executable_start as the lowest text
> address, so using the entry point address as a fallback is no
> longer necessary.  As a result, overriding <entry.h> is only
> necessary if the entry point is not called _start.
>
> 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, powerpc-linux-gnu, powerpc64-linux-gnu,
> powerpc64le-linux-gnu, x86_64-linux-gnu.  Built with
> build-many-glibcs.py.
>
> ---
> v2: Remove TEXT_START instead of generalizing it.
>
>  csu/gmon-start.c                  | 29 +++--------------------------
>  sysdeps/hppa/entry.h              | 13 -------------
>  sysdeps/ia64/entry.h              | 13 -------------
>  sysdeps/powerpc/powerpc64/entry.h | 37 -------------------------------------
>  4 files changed, 3 insertions(+), 89 deletions(-)
>
> diff --git a/csu/gmon-start.c b/csu/gmon-start.c
> index 344606a676..260c7613e2 100644
> --- a/csu/gmon-start.c
> +++ b/csu/gmon-start.c
> @@ -38,32 +38,12 @@
>  #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[];
>
>  /* 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")));
> +extern const char __executable_start[] __attribute__ ((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[];
>
>  #if !ELF_INITFINI
>  /* Instead of defining __gmon_start__ globally in gcrt1.o, we make it
> @@ -97,10 +77,7 @@ __gmon_start__ (void)
>    called = 1;
>
>    /* Start keeping profiling records.  */
> -  if (&executable_start != NULL)
> -    __monstartup ((u_long) &executable_start, (u_long) &etext);
> -  else
> -    __monstartup ((u_long) TEXT_START, (u_long) &etext);
> +  __monstartup ((u_long) &__executable_start, (u_long) &etext);
>
>    /* Call _mcleanup before exiting; it will write out gmon.out from the
>       collected data.  */
> diff --git a/sysdeps/hppa/entry.h b/sysdeps/hppa/entry.h
> deleted file mode 100644
> index 5ea5b47448..0000000000
> --- a/sysdeps/hppa/entry.h
> +++ /dev/null
> @@ -1,13 +0,0 @@
> -#ifndef __ASSEMBLY__
> -extern void _start (void);
> -#endif
> -
> -/* 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);
> 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/powerpc/powerpc64/entry.h b/sysdeps/powerpc/powerpc64/entry.h
> deleted file mode 100644
> index 99c81cb982..0000000000
> --- a/sysdeps/powerpc/powerpc64/entry.h
> +++ /dev/null
> @@ -1,37 +0,0 @@
> -/* Finding the entry point and start of text.  PowerPC64 version.
> -   Copyright (C) 2002-2021 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/>.  */
> -
> -
> -#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);
> -
> -/* 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 \
> -  ({ extern unsigned long int _start_as_data[] asm ("_start");  \
> -     _start_as_data[0]; })
> -#endif
>

LGTM.

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>

Thanks.