[langdale,master,v3] rust: Do not use default compiler flags defined in CC crate

Rust crates build dependecy C libraries using "CC" crate.
This crate adds some default compiler parameters depending on target arch.
For some target archs these parameters conflict with the parameters defined by OE.

Warnings/errors like this can be seen in the case:

cc1: error: switch '-mcpu=cortex-a15' conflicts with switch '-march=armv7-a+fp' [-Werror]

Lets use only the OE parameters by exporting CRATE_CC_NO_DEFAULTS.
https://github.com/rust-lang/cc-rs#external-configuration-via-environment-variables

This patch fixes https://bugzilla.yoctoproject.org/show_bug.cgi?id=14947

Signed-off-by: Anton Antonov <Anton.Antonov@arm.com>
---
 meta/classes-recipe/rust-target-config.bbclass | 13 +++++++++++++
 1 file changed, 13 insertions(+)

Hello,

this fails on the autobuilders:

https://autobuilder.yoctoproject.org/typhoon/#/builders/64/builds/6362/steps/11/logs/stdio
https://autobuilder.yoctoproject.org/typhoon/#/builders/52/builds/6274/steps/12/logs/stdio

On 20/12/2022 11:24:59+0000, Anton Antonov wrote:
> Rust crates build dependecy C libraries using "CC" crate.
> This crate adds some default compiler parameters depending on target arch.
> For some target archs these parameters conflict with the parameters defined by OE.
> 
> Warnings/errors like this can be seen in the case:
> 
> cc1: error: switch '-mcpu=cortex-a15' conflicts with switch '-march=armv7-a+fp' [-Werror]
> 
> Lets use only the OE parameters by exporting CRATE_CC_NO_DEFAULTS.
> https://github.com/rust-lang/cc-rs#external-configuration-via-environment-variables
> 
> This patch fixes https://bugzilla.yoctoproject.org/show_bug.cgi?id=14947
> 
> Signed-off-by: Anton Antonov <Anton.Antonov@arm.com>
> ---
>  meta/classes-recipe/rust-target-config.bbclass | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/meta/classes-recipe/rust-target-config.bbclass b/meta/classes-recipe/rust-target-config.bbclass
> index 2710b4325d..5685897462 100644
> --- a/meta/classes-recipe/rust-target-config.bbclass
> +++ b/meta/classes-recipe/rust-target-config.bbclass
> @@ -401,3 +401,16 @@ python do_rust_gen_targets () {
>  addtask rust_gen_targets after do_patch before do_compile
>  do_rust_gen_targets[dirs] += "${RUST_TARGETS_DIR}"
>  
> +# For building C dependecies use only compiler parameters defined in OE-core
> +# and ignore the default parameters defined in the CC crate.
> +# https://github.com/rust-lang/cc-rs#external-configuration-via-environment-variables
> +
> +# The CC crate checks for CRATE_CC_NO_DEFAULTS existence not value.
> +# Even empty CRATE_CC_NO_DEFAULTS will be taken into account.
> +# For rust native recipes we still rely on the CC crate parameters.
> +# Currently it's not possible to export a variable conditionally,
> +# so, let's export it for class-target only
> +
> +do_compile:prepend:class-target() {
> +    export CRATE_CC_NO_DEFAULTS=1
> +}
> -- 
> 2.25.1
> 

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Hi Alexandre,

It looks like in rust classes we don't define compiler parameter not only for native recipes, but for x86 targets also. I need to think about a different approach to fix the issue.

Cheers,

Anton