Re: [lttng-dev] [PATCH 1/7] Require __atomic builtins to build

[Mathieu Desnoyers via lttng-dev <lttng-dev@lists.lttng.org>]

On 2023-03-21 09:30, Ondřej Surý via lttng-dev wrote:
> Add autoconf checks for all __atomic builtins that urcu require, and
> adjust the gcc and clang versions in the README.md.
> 
> Signed-off-by: Ondřej Surý <ondrej@sury.org>
> ---
>   README.md    | 33 +++++++++------------------------
>   configure.ac | 15 +++++++++++++++
>   2 files changed, 24 insertions(+), 24 deletions(-)
> 
> diff --git a/README.md b/README.md
> index ba5bb08..a65a07a 100644
> --- a/README.md
> +++ b/README.md
> @@ -68,30 +68,15 @@ Should also work on:
>   
>   (more testing needed before claiming support for these OS).
>   
> -Linux ARM depends on running a Linux kernel 2.6.15 or better, GCC 4.4 or
> -better.
> -
> -The C compiler used needs to support at least C99. The C++ compiler used
> -needs to support at least C++11.
> -
> -The GCC compiler versions 3.3, 3.4, 4.0, 4.1, 4.2, 4.3, 4.4 and 4.5 are
> -supported, with the following exceptions:
> -
> -  - GCC 3.3 and 3.4 have a bug that prevents them from generating volatile
> -    accesses to offsets in a TLS structure on 32-bit x86. These versions are
> -    therefore not compatible with `liburcu` on x86 32-bit
> -    (i386, i486, i586, i686).
> -    The problem has been reported to the GCC community:
> -    <http://www.mail-archive.com/gcc-bugs@gcc.gnu.org/msg281255.html>
> -  - GCC 3.3 cannot match the "xchg" instruction on 32-bit x86 build.
> -    See <http://kerneltrap.org/node/7507>
> -  - Alpha, ia64 and ARM architectures depend on GCC 4.x with atomic builtins
> -    support. For ARM this was introduced with GCC 4.4:
> -    <http://gcc.gnu.org/gcc-4.4/changes.html>.
> -  - Linux aarch64 depends on GCC 5.1 or better because prior versions
> -    perform unsafe access to deallocated stack.
> -
> -Clang version 3.0 (based on LLVM 3.0) is supported.
> +Linux ARM depends on running a Linux kernel 2.6.15 or better.
> +
> +The C compiler used needs to support at least C99 and __atomic
> +builtins. The C++ compiler used needs to support at least C++11
> +and __atomic builtins.
> +
> +The GCC compiler versions 4.7 or better are supported.
> +
> +Clang version 3.1 (based on LLVM 3.1) is supported.
>   
>   Glibc >= 2.4 should work but the older version we test against is
>   currently 2.17.
> diff --git a/configure.ac b/configure.ac
> index 909cf1d..cb7ba18 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -198,6 +198,21 @@ AC_SEARCH_LIBS([clock_gettime], [rt], [
>     AC_DEFINE([CONFIG_RCU_HAVE_CLOCK_GETTIME], [1], [clock_gettime() is detected.])
>   ])
>   
> +# Require __atomic builtins
> +AC_COMPILE_IFELSE(
> +	[AC_LANG_PROGRAM(
> +		[[int x, y;]],
> +		[[__atomic_store_n(&x, 0, __ATOMIC_RELEASE);
> +		  __atomic_load_n(&x, __ATOMIC_CONSUME);
> +		  y = __atomic_exchange_n(&x, 1, __ATOMIC_ACQ_REL);
> +		  __atomic_compare_exchange_n(&x, &y, 0, 0, __ATOMIC_ACQ_REL, __ATOMIC_CONSUME);
> +		  __atomic_add_fetch(&x, 1, __ATOMIC_ACQ_REL);
> +		  __atomic_sub_fetch(&x, 1, __ATOMIC_ACQ_REL);
> +		  __atomic_and_fetch(&x, 0x01, __ATOMIC_ACQ_REL);
> +		  __atomic_or_fetch(&x, 0x01, __ATOMIC_ACQ_REL);
> +		  __atomic_thread_fence(__ATOMIC_ACQ_REL)]])],

I think we also want to test for __atomic_signal_fence here.

Thanks,

Mathieu


> +	[],
> +	[AC_MSG_ERROR([The compiler does not support __atomic builtins])])
>   
>   ##                             ##
>   ## Optional features selection ##

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com

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