Re: [PATCH] Reduce <limits.h> pollution due to dynamic PTHREAD_STACK_MIN

[Carlos O'Donell via Libc-alpha <libc-alpha@sourceware.org>]

On 7/12/21 8:53 AM, Florian Weimer wrote:
> <limits.h> used to be a header file with no declarations.
> GCC's libgomp includes in a #pragma GCC visibility hidden block.
> Including <unistd.h> from <limits.h> (indirectly) declares everything
> in <unistd.h> with hidden visibility, resulting in linker failures.
> 
> This commit avoids C declarations in assembler mode and only declares
> __sysconf in <limits.h> (and not the entire contents of <unistd.h>).
> The __sysconf symbol is already part of the ABI.  PTHREAD_STACK_MIN
> is no longer defined for __USE_DYNAMIC_STACK_SIZE && __ASSEMBLER__
> because there is no possible definition.
> 
> Additionally, PTHREAD_STACK_MIN is now defined by <pthread.h> for
> __USE_MISC because this is what developers expect based on the macro
> name.  It also helps to avoid libgomp linker failures in GCC because
> libgomp includes <pthread.h> before its visibility hacks.

We absolutely want to be able to build glibc with an unmodified released
gcc, and requiring a fix would impact usability. Therefore regardless of
the exact technical merits of this fix, I think it goes in the right
direction. At a later date we can cleanup this technical debt.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

> ---
>  include/bits/local_lim.h                           |  7 -----
>  nptl/tst-minstack-exit.c                           |  3 +++
>  sysdeps/nptl/pthread.h                             |  4 ++-
>  sysdeps/unix/sysv/linux/Makefile                   |  2 +-
>  sysdeps/unix/sysv/linux/bits/local_lim.h           | 10 ++-----
>  .../sysv/linux/bits/pthread_stack_min-dynamic.h    | 31 ++++++++++++++++++++++
>  .../linux/include/bits/pthread_stack_min-dynamic.h |  7 +++++
>  7 files changed, 47 insertions(+), 17 deletions(-)
> 
> diff --git a/include/bits/local_lim.h b/include/bits/local_lim.h
> deleted file mode 100644
> index 46d82dc729..0000000000
> --- a/include/bits/local_lim.h
> +++ /dev/null
> @@ -1,7 +0,0 @@
> -/* Don't define PTHREAD_STACK_MIN to sysconf (_SC_THREAD_STACK_MIN) for
> -   glibc build.  */
> -#if !defined _ISOMAC
> -# undef __USE_DYNAMIC_STACK_SIZE
> -#endif
> -
> -#include_next <bits/local_lim.h>

OK. This moves from bits/local_lim.h -> sysdeps/unix/sysv/linux/include/bits/pthread_stack_min-dynamic.h

> diff --git a/nptl/tst-minstack-exit.c b/nptl/tst-minstack-exit.c
> index 4e7dc3e786..e577924178 100644
> --- a/nptl/tst-minstack-exit.c
> +++ b/nptl/tst-minstack-exit.c
> @@ -24,6 +24,9 @@
>  #include <support/check.h>
>  #include <support/xthread.h>
>  
> +_Static_assert (__SC_THREAD_STACK_MIN_VALUE == _SC_THREAD_STACK_MIN,
> +                "__SC_THREAD_STACK_MIN_VALUE is correct");
> +

OK. Keeps the constant value checked so it doesn't change.

>  static void *
>  threadfunc (void *closure)
>  {
> diff --git a/sysdeps/nptl/pthread.h b/sysdeps/nptl/pthread.h
> index 52e2eadbfc..f1b7f2bdc6 100644
> --- a/sysdeps/nptl/pthread.h
> +++ b/sysdeps/nptl/pthread.h
> @@ -29,7 +29,9 @@
>  #include <bits/types/struct_timespec.h>
>  #include <bits/types/__sigset_t.h>
>  #include <bits/types/struct___jmp_buf_tag.h>
> -
> +#ifdef __USE_MISC
> +# include <bits/pthread_stack_min-dynamic.h>
> +#endif

OK. Include it early (everyone using pthread.h would expect it).

>  
>  /* Detach state.  */
>  enum
> diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
> index 7d43dc95f2..8257e5b548 100644
> --- a/sysdeps/unix/sysv/linux/Makefile
> +++ b/sysdeps/unix/sysv/linux/Makefile
> @@ -109,7 +109,7 @@ sysdep_headers += sys/mount.h sys/acct.h \
>  		  bits/types/struct_semid64_ds_helper.h \
>  		  bits/types/struct_shmid64_ds.h \
>  		  bits/types/struct_shmid64_ds_helper.h \
> -		  bits/pthread_stack_min.h
> +		  bits/pthread_stack_min.h bits/pthread_stack_min-dynamic.h

OK.

>  
>  tests += tst-clone tst-clone2 tst-clone3 tst-fanotify tst-personality \
>  	 tst-quota tst-sync_file_range tst-sysconf-iov_max tst-ttyname \
> diff --git a/sysdeps/unix/sysv/linux/bits/local_lim.h b/sysdeps/unix/sysv/linux/bits/local_lim.h
> index 0b1c7f40be..b8f89236bc 100644
> --- a/sysdeps/unix/sysv/linux/bits/local_lim.h
> +++ b/sysdeps/unix/sysv/linux/bits/local_lim.h
> @@ -77,14 +77,8 @@
>     priority level.  */
>  #define AIO_PRIO_DELTA_MAX	20
>  
> -/* Minimum size for a thread.  We are free to choose a reasonable value.  */
> -#undef PTHREAD_STACK_MIN
> -#if defined __USE_DYNAMIC_STACK_SIZE && __USE_DYNAMIC_STACK_SIZE
> -# include <unistd.h>
> -# define PTHREAD_STACK_MIN	sysconf (_SC_THREAD_STACK_MIN)
> -#else
> -# include <bits/pthread_stack_min.h>
> -#endif
> +/* Arrange for the definition of PTHREAD_STACK_MIN.  */
> +#include <bits/pthread_stack_min-dynamic.h>

OK.

>  
>  /* Maximum number of timer expiration overruns.  */
>  #define DELAYTIMER_MAX	2147483647
> diff --git a/sysdeps/unix/sysv/linux/bits/pthread_stack_min-dynamic.h b/sysdeps/unix/sysv/linux/bits/pthread_stack_min-dynamic.h
> new file mode 100644
> index 0000000000..5f5fc5f024
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/bits/pthread_stack_min-dynamic.h
> @@ -0,0 +1,31 @@
> +/* Definition of PTHREAD_STACK_MIN, possibly dynamic.
> +   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/>.  */
> +
> +#ifndef PTHREAD_STACK_MIN
> +# if defined __USE_DYNAMIC_STACK_SIZE && __USE_DYNAMIC_STACK_SIZE
> +#  ifndef __ASSEMBLER__
> +#   define __SC_THREAD_STACK_MIN_VALUE 75
> +__BEGIN_DECLS
> +extern long int __sysconf (int __name) __THROW;
> +__END_DECLS
> +#   define PTHREAD_STACK_MIN __sysconf (__SC_THREAD_STACK_MIN_VALUE)

OK. Decouple from the actual definition of the sysconf value.

> +#  endif
> +# else
> +#  include <bits/pthread_stack_min.h>
> +# endif
> +#endif
> diff --git a/sysdeps/unix/sysv/linux/include/bits/pthread_stack_min-dynamic.h b/sysdeps/unix/sysv/linux/include/bits/pthread_stack_min-dynamic.h
> new file mode 100644
> index 0000000000..d66f584b21
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/include/bits/pthread_stack_min-dynamic.h
> @@ -0,0 +1,7 @@
> +/* Don't define PTHREAD_STACK_MIN to __sysconf (_SC_THREAD_STACK_MIN)
> +   for glibc build.  */
> +#ifdef _ISOMAC
> +# include <sysdeps/unix/sysv/linux/bits/pthread_stack_min-dynamic.h>
> +#else
> +# include <bits/pthread_stack_min.h>
> +#endif
> 

OK.

-- 
Cheers,
Carlos.