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Bug#1069862: blktrace: FTBFS on ppc64el in Ubuntu (-O3?) due to wrong code analysis

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  Bug#1069862: blktrace: FTBFS on ppc64el in Ubuntu (-O3?) due to wrong code analysis Daichi Fukui <a.dog.will.talk@akane.waseda.jp> - 2024-09-23 06:40 +0200
    Bug#1069862: blktrace: FTBFS on ppc64el in Ubuntu (-O3?) due to wrong code analysis Chris Hofstaedtler <zeha@debian.org> - 2024-09-23 19:10 +0200
      Bug#1069862: blktrace: FTBFS on ppc64el in Ubuntu (-O3?) due to wrong code analysis Daichi Fukui <a.dog.will.talk@akane.waseda.jp> - 2024-09-25 15:50 +0200

#1214003 — Bug#1069862: blktrace: FTBFS on ppc64el in Ubuntu (-O3?) due to wrong code analysis

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Hello Steve,

> It's possible/likely that this build failure is caused by the use of -O3
by
> default for ppc64el builds in Ubuntu; so the attached patch, while it
fixes
> the problem in Ubuntu and should be harmless in Debian, may not be
something
> you want to apply as-is.  Perhaps you would prefer to use $(filter
-O3,...)
> instead?

Thank you for reporting this issue.

Your idea of using $(filter -O3,...) looks good to me, but I would like to
clarify one thing.

When I tried to reproduce the issue on ppc64el with Debian unstable as of
September 22, 2024, I was unable to do so.
According to the build log[0] on ppc64el, it appears that the -O2 option is
used for the build rather than -O3.

For further investigation, if the following change is applied to d/rules,
the issue is reproduced on ppc64el with Debian unstable, but that is not
what we want to do.

```
--- ../blktrace/debian/rules    2024-08-18 06:21:55.984000000 +0000
+++ debian/rules        2024-09-22 06:48:37.696000000 +0000
@@ -5,7 +5,7 @@
 include /usr/share/dpkg/architecture.mk
 include /usr/share/dpkg/pkg-info.mk

-CFLAGS += -Wall -Wextra -Wno-shadow -Werror -g
+CFLAGS += -Wall -Wextra -Wno-shadow -Werror -g -O3

 export DEB_BUILD_MAINT_OPTIONS = hardening=+all future=+all qa=+all
reproducible=+all
```

Additionally, the -O2 option is used for all CPU architectures in Ubuntu
except for ppc64el[1], which makes me wonder why -O3 is used for ppc64el in
Ubuntu.
Do you have any idea why -O3 is used only for ppc64el in Ubuntu?
I would like to know whether this issue is specific to Ubuntu.

[0]
https://buildd.debian.org/status/fetch.php?pkg=blktrace&arch=ppc64el&ver=1.2.0-5&stamp=1551092176&raw=0
[1] https://launchpad.net/ubuntu/+source/blktrace/1.2.0-5build1

Best regards,
Fukui

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#1214046

On Mon, Sep 23, 2024 at 01:31:51PM +0900, Daichi Fukui wrote:
> Do you have any idea why -O3 is used only for ppc64el in Ubuntu?
> I would like to know whether this issue is specific to Ubuntu.

Ubuntu sets -O3 as default in their dpkg, for ppc64el:

https://github.com/guillemj/dpkg/blob/29684731af629e9103306b7716663e44224e6cab/scripts/Dpkg/Vendor/Ubuntu.pm#L125

Chris

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#1214233

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Hello Chris,
CC: Steve

Thank you for your response.

After reviewing the source code of dpkg, I now understand that the -O3
optimisation level is set by default for ppc64el in Ubuntu.
However, it appears that there is no code to change the optimisation level
based on CPU architecture in Debian.
Therefore, I believe this issue is specific to Ubuntu.

If there are no objections, we can close this issue.
I am happy to continue this discussion if you’d like.

Best regards,
Fukui

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