Re: [Buildroot] [PATCH] package/uclibc: Fix build when RVA is disabled

[Thomas Petazzoni via buildroot <buildroot@buildroot.org>]

Hello,

+Waldemar in Cc, uclibc stuff :-)

On Mon,  2 Sep 2024 13:59:56 -0400
Jesse Taube <mr.bossman075@gmail.com> wrote:

> If the RVA option is disabled uclibc won't build with Shared libraries
> enabled or Threads enabled. Add guards against this.

Meh, this looks weird to me, and I'd like some better understanding
before adding "random" guards.

> When the RVA option is disabled, the build fails with the
> following errors:
> With Threads enabled:
> 
>   LD libuClibc-1.0.48.so
> riscv64-buildroot-linux-uclibc/bin/ld: libc/libc_so.a(err.os): in function `.L0 ':
> err.c:(.text+0xa0): undefined reference to `__atomic_compare_exchange_4'
> riscv64-buildroot-linux-uclibc/bin/ld: libc/libc_so.a(err.os): in function `.L6':
> err.c:(.text+0x138): undefined reference to `__atomic_exchange_4'
> riscv64-buildroot-linux-uclibc/bin/ld: libc/libc_so.a(__cxa_finalize.os): in function `.L3':
> __cxa_finalize.c:(.text+0xac): undefined reference to `__atomic_compare_exchange_8'
> riscv64-buildroot-linux-uclibc/bin/ld: libc/libc_so.a(fork.oS): in function `.L23':
> fork.c:(.text+0x130): undefined reference to `__atomic_fetch_add_4'
> riscv64-buildroot-linux-uclibc/bin/ld: libc/libc_so.a(sem_timedwait.oS): in function `.L5':
> sem_timedwait.c:(.text+0xe0): undefined reference to `__atomic_fetch_add_8'
> 
> With Shared libraries enabled:
> 
>   LD libuClibc-1.0.48.so
> riscv64-buildroot-linux-uclibc/bin/ld: libc/libc_so.a(__cxa_finalize.os): in function `.L3':
> __cxa_finalize.c:(.text+0xa4): undefined reference to `__atomic_compare_exchange_8'
> 
> Signed-off-by: Jesse Taube <Mr.Bossman075@gmail.com>
> ---
>  arch/Config.in           | 2 +-
>  package/uclibc/Config.in | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/Config.in b/arch/Config.in
> index f39c33ef7f..d0052782be 100644
> --- a/arch/Config.in
> +++ b/arch/Config.in
> @@ -431,7 +431,7 @@ choice
>  config BR2_BINFMT_ELF
>  	bool "ELF"
>  	depends on BR2_USE_MMU
> -	select BR2_BINFMT_SUPPORTS_SHARED
> +	select BR2_BINFMT_SUPPORTS_SHARED if !BR2_riscv || BR2_RISCV_ISA_RVA

Why this? This is no covered in your commit log.

>  	help
>  	  ELF (Executable and Linkable Format) is a format for libraries
>  	  and executables used across different architectures and
> diff --git a/package/uclibc/Config.in b/package/uclibc/Config.in
> index 73ddd5ef58..f7edd417c6 100644
> --- a/package/uclibc/Config.in
> +++ b/package/uclibc/Config.in
> @@ -78,13 +78,13 @@ choice
>  
>  config BR2_PTHREADS_NATIVE
>  	bool "Native POSIX Threading (NPTL)"
> -	depends on BR2_USE_MMU
> +	depends on BR2_USE_MMU && (!BR2_riscv || BR2_RISCV_ISA_RVA)
>  	select BR2_TOOLCHAIN_HAS_THREADS
>  	select BR2_TOOLCHAIN_HAS_THREADS_NPTL
>  
>  config BR2_PTHREADS
>  	bool "linuxthreads"
> -	depends on !BR2_aarch64 && !BR2_aarch64_be
> +	depends on !BR2_aarch64 && !BR2_aarch64_be && (!BR2_riscv || BR2_RISCV_ISA_RVA)
>  	select BR2_TOOLCHAIN_HAS_THREADS

I would really like to hear back from Waldemar on this.

uClibc supports architectures that don't have atomic support (such as
ARC750/ARC770), so it is somewhat surprising that it wouldn't support
RISC-V without atomics. So let's try to understand the real problem and
find the correct solution rather than papering over the problem in a
very custom/architecture-specific way.

Thanks!

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering and training
https://bootlin.com
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