[v4,2/3] Linux: Implement a useful version of _startup_fatal

  On i386 and ia64, the TCB is not available at this point.
---
v4: Unchanged.
v3: Use 2022 copyright year.  Fix “statup” typo.  Use __message_length
    local variable in _startup_fatal.
 sysdeps/unix/sysv/linux/i386/startup.h | 23 +++------------
 sysdeps/unix/sysv/linux/ia64/startup.h | 22 +++++++++++++++
 sysdeps/unix/sysv/linux/startup.h      | 39 ++++++++++++++++++++++++++
 3 files changed, 65 insertions(+), 19 deletions(-)
 create mode 100644 sysdeps/unix/sysv/linux/ia64/startup.h
 create mode 100644 sysdeps/unix/sysv/linux/startup.h
  

On Mai 05 2022, Florian Weimer via Libc-alpha wrote:

> +/* Avoid a run-time invocation of strlen.  */
> +#define _startup_fatal(message)                                         \
> +  do                                                                    \
> +    {                                                                   \
> +      size_t __message_length = __builtin_strlen (message);             \
> +      if (! __builtin_constant_p (__message_length))                    \
> +        {                                                               \
> +          extern void _startup_fatal_not_constant (void);               \
> +          _startup_fatal_not_constant ();                               \
> +        }                                                               \

I think that could use _Static_assert.
  

* Andreas Schwab:

> On Mai 05 2022, Florian Weimer via Libc-alpha wrote:
>
>> +/* Avoid a run-time invocation of strlen.  */
>> +#define _startup_fatal(message)                                         \
>> +  do                                                                    \
>> +    {                                                                   \
>> +      size_t __message_length = __builtin_strlen (message);             \
>> +      if (! __builtin_constant_p (__message_length))                    \
>> +        {                                                               \
>> +          extern void _startup_fatal_not_constant (void);               \
>> +          _startup_fatal_not_constant ();                               \
>> +        }                                                               \
>
> I think that could use _Static_assert.

It only works for simple cases, not for arguments that require constant
progagation:

libc-tls.c: In function ‘__libc_setup_tls’:
../sysdeps/unix/sysv/linux/startup.h:29:23: error: expression in static assertion is not constant
   29 |       _Static_assert (__builtin_constant_p (__message_length),          \
      |                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Thanks,
Florian
  

On 05/05/2022 12:07, Florian Weimer via Libc-alpha wrote:
> On i386 and ia64, the TCB is not available at this point.

LGTM, thanks.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
> v4: Unchanged.
> v3: Use 2022 copyright year.  Fix “statup” typo.  Use __message_length
>     local variable in _startup_fatal.
>  sysdeps/unix/sysv/linux/i386/startup.h | 23 +++------------
>  sysdeps/unix/sysv/linux/ia64/startup.h | 22 +++++++++++++++
>  sysdeps/unix/sysv/linux/startup.h      | 39 ++++++++++++++++++++++++++
>  3 files changed, 65 insertions(+), 19 deletions(-)
>  create mode 100644 sysdeps/unix/sysv/linux/ia64/startup.h
>  create mode 100644 sysdeps/unix/sysv/linux/startup.h
> 
> diff --git a/sysdeps/unix/sysv/linux/i386/startup.h b/sysdeps/unix/sysv/linux/i386/startup.h
> index 67c9310f3a..213805d7d2 100644
> --- a/sysdeps/unix/sysv/linux/i386/startup.h
> +++ b/sysdeps/unix/sysv/linux/i386/startup.h
> @@ -1,5 +1,5 @@
>  /* Linux/i386 definitions of functions used by static libc main startup.
> -   Copyright (C) 2017-2022 Free Software Foundation, Inc.
> +   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
> @@ -16,22 +16,7 @@
>     License along with the GNU C Library; if not, see
>     <https://www.gnu.org/licenses/>.  */
>  
> -#if BUILD_PIE_DEFAULT
> -/* Can't use "call *%gs:SYSINFO_OFFSET" during statup in static PIE.  */
> -# define I386_USE_SYSENTER 0
> +/* Can't use "call *%gs:SYSINFO_OFFSET" during startup.  */
> +#define I386_USE_SYSENTER 0
>  
> -# include <sysdep.h>
> -# include <abort-instr.h>
> -
> -__attribute__ ((__noreturn__))
> -static inline void
> -_startup_fatal (const char *message __attribute__ ((unused)))
> -{
> -  /* This is only called very early during startup in static PIE.
> -     FIXME: How can it be improved?  */
> -  ABORT_INSTRUCTION;
> -  __builtin_unreachable ();
> -}
> -#else
> -# include_next <startup.h>
> -#endif
> +#include_next <startup.h>
> diff --git a/sysdeps/unix/sysv/linux/ia64/startup.h b/sysdeps/unix/sysv/linux/ia64/startup.h
> new file mode 100644
> index 0000000000..77f29f15a2
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/ia64/startup.h
> @@ -0,0 +1,22 @@
> +/* Linux/ia64 definitions of functions used by static libc main startup.
> +   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/>.  */
> +
> +/* This code is used before the TCB is set up.  */
> +#define IA64_USE_NEW_STUB 0
> +
> +#include_next <startup.h>
> diff --git a/sysdeps/unix/sysv/linux/startup.h b/sysdeps/unix/sysv/linux/startup.h
> new file mode 100644
> index 0000000000..39859b404a
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/startup.h
> @@ -0,0 +1,39 @@
> +/* Linux definitions of functions used by static libc main startup.
> +   Copyright (C) 2017-2022 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/>.  */
> +
> +#ifdef SHARED
> +# include_next <startup.h>
> +#else
> +# include <sysdep.h>
> +
> +/* Avoid a run-time invocation of strlen.  */
> +#define _startup_fatal(message)                                         \
> +  do                                                                    \
> +    {                                                                   \
> +      size_t __message_length = __builtin_strlen (message);             \
> +      if (! __builtin_constant_p (__message_length))                    \
> +        {                                                               \
> +          extern void _startup_fatal_not_constant (void);               \
> +          _startup_fatal_not_constant ();                               \
> +        }                                                               \
> +      INTERNAL_SYSCALL_CALL (write, STDERR_FILENO, (message),           \
> +                             __message_length);                         \
> +      INTERNAL_SYSCALL_CALL (exit_group, 127);                          \
> +    }                                                                   \
> +  while (0)
> +#endif  /* !SHARED */