Re: [OE-core] [PATCH 1/2] qemu: retain default trace backend if 'ust' is not enabled

[Richard Purdie <richard.purdie@linuxfoundation.org>]

On Mon, 2023-04-03 at 16:37 +0200, Thomas De Schampheleire wrote:
> The qemu build system enables the 'log' trace backend by default, if no
> explicit choice was made with '--enable-trace-backend=CHOICE'.
> 
> However, the qemu recipe uses the following PACKAGECONFIG line:
>     PACKAGECONFIG[ust] = "--enable-trace-backend=ust,--enable-trace-backend=nop,lttng-ust,"
> 
> which means that the 'nop' trace backend will be explicitly selected if the
> 'ust' feature is not enabled. The 'nop' backend removes almost all trace
> points at compile time, and thus basically means 'disable tracing'.
> 
> To retain the default trace backend if 'ust' is not enabled, the above
> PACKAGECONFIG line should either explicitly fall back to the 'log' backend,
> or not provide any value for the 'disabled' case. This commit chooses the
> latter to not make any assumption about the upstream default.
> 
> Signed-off-by: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
> ---
>  meta/recipes-devtools/qemu/qemu.inc | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/meta/recipes-devtools/qemu/qemu.inc b/meta/recipes-devtools/qemu/qemu.inc
> index b41055fe5d..ae99a9e87b 100644
> --- a/meta/recipes-devtools/qemu/qemu.inc
> +++ b/meta/recipes-devtools/qemu/qemu.inc
> @@ -207,7 +207,7 @@ PACKAGECONFIG[libudev] = "--enable-libudev,--disable-libudev,eudev"
>  PACKAGECONFIG[attr] = "--enable-attr,--disable-attr,attr,"
>  PACKAGECONFIG[rbd] = "--enable-rbd,--disable-rbd,ceph,ceph"
>  PACKAGECONFIG[vhost] = "--enable-vhost-net,--disable-vhost-net,,"
> -PACKAGECONFIG[ust] = "--enable-trace-backend=ust,--enable-trace-backend=nop,lttng-ust,"
> +PACKAGECONFIG[ust] = "--enable-trace-backend=ust,,lttng-ust,"
>  PACKAGECONFIG[pie] = "--enable-pie,--disable-pie,,"
>  PACKAGECONFIG[seccomp] = "--enable-seccomp,--disable-seccomp,libseccomp"
>  # libnfs is currently provided by meta-kodi

This triggered reproducible build test failures:

https://autobuilder.yoctoproject.org/typhoon/#/builders/117/builds/2659/steps/12/logs/stdio

which leads to:

http://autobuilder.yocto.io/pub/repro-fail/oe-reproducible-20230403-itxd_s50/packages/diff-html/

i.e. the paths to files is being encoded the target source package
files.

We'll need to resolve that issue before we can turn the default tracing
on.

Cheers,

Richard