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compile stage4 on Rpi4 for Rpi3 - 32bit
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antonellocaroli
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PostPosted: Sat Dec 28, 2019 9:22 am    Post subject: compile stage4 on Rpi4 for Rpi3 - 32bit Reply with quote

You can compile a stage4-32bit on Rpi4 for Rpi3?

using in make.conf CFLAGS="-O2 -march=armv7-a -mfpu=neon-vfpv4 -mfloat-abi=hard"

???


other thing:
weird thing I realized on rpi3 march=native from this result, isn't it wrong?

Code:
gcc -v -E -x c /dev/null -o /dev/null -march=native 2>&1 | grep /cc1
 /usr/libexec/gcc/armv7a-unknown-linux-gnueabihf/9.2.0/cc1 -E -quiet -v /dev/null -o /dev/null -mfloat-abi=hard -mfpu=vfpv3-d16 -mtls-dialect=gnu -marm -march=armv8-a+crc+simd
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NeddySeagoon
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PostPosted: Sat Dec 28, 2019 12:23 pm    Post subject: Reply with quote

antonellocaroli,

Lets clarify the problem before I try to answer.
Both the Pi3 and P4 can run in 32 bit or 64 bit mode.

ARM CPUs can switch modes as required so its possible to run 32 bit code on an otherwise 64 bit system.
The other way round does not work as a 64 bit kernel is required to support 64 bit code.
There is no intention to implement multilib on armv8, so its not possible to mix 64 bit and 32 bit code in the same install without keeping them separate yourself, eg a 32 bit chroot on a 64 bit system.

I think the answer to your question is yes but ...
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antonellocaroli
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PostPosted: Sat Dec 28, 2019 12:44 pm    Post subject: Reply with quote

so I should probably use

CFLAGS="-march=native -O2 -pipe".

since it is on both rpi3 and rpi4

the result is the same by checking with
Code:
gcc -v -E -x c /dev/null -o /dev/null -march=native 2>&1 | grep /cc1
 /usr/libexec/gcc/armv7a-unknown-linux-gnueabihf/9.2.0/cc1 -E -quiet -v /dev/null -o /dev/null -mfloat-abi=hard -mfpu=vfpv3-d16 -mtls-dialect=gnu -marm -march=armv8-a+crc+simd


???
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NeddySeagoon
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PostPosted: Sat Dec 28, 2019 1:02 pm    Post subject: Reply with quote

antonellocaroli,

Its still net clear.

You have a Raspberry Pi4 that you wish to use as a build system for a 32 bit Pi3.
What install is on the Raspberry Pi4?
Is it 64 bit or 32 bit?

The Raspberry Pi3 will run a 32 bit install and you will build on the Pi4 for it.

Given that on both systems you get the same output from
Code:
gcc -v -E -x c /dev/null -o /dev/null -march=native 2>&1 | grep /cc1

They will run the same userspace code.

Howewer ..
Code:
/usr/libexec/gcc/armv7a-unknown-linux-gnueabihf/
if correct for the P3.
The Pi4 is an armv7l CPU.
armv7a will run on both CPU though.
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antonellocaroli
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PostPosted: Sat Dec 28, 2019 1:20 pm    Post subject: Reply with quote

on pi4 now runs an installation made on pi3 using in the make.conf

Code:

CFLAGS="-march=native -O2 -pipe"
CHOST="armv7a-unknown-linux-gnueabihf"


I just want to use pi4 to upgrade the system, like gcc etc...
and then switch the system to pi3 again.
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NeddySeagoon
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PostPosted: Sat Dec 28, 2019 1:38 pm    Post subject: Reply with quote

antonellocaroli,

Thats fine. The same userspace code will run on both systems.
The kernels and device trees are the only changes.
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