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[Solved] Where is CONFIG_DEBUG_INFO_BTF?
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eborg
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PostPosted: Wed Dec 27, 2023 8:32 pm    Post subject: [Solved] Where is CONFIG_DEBUG_INFO_BTF? Reply with quote

I have a 6.1.67 kernel and am trying to work with libbpf which calls for a kernel built with CONFIG_DEBUG_INFO_BTF=y. A search in 'menuconfig' says the module is here ...

-> Kernel hacking
-> Compile-time checks and compiler options
-> Generate BTF typeinfo (DEBUG_INFO_BTF [=n])

But when I go there, I do not see the option. How else can I find a way to enable these options witin the kernel?


Last edited by eborg on Thu Dec 28, 2023 1:53 am; edited 1 time in total
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grknight
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PostPosted: Wed Dec 27, 2023 9:02 pm    Post subject: Reply with quote

If you press 'z' in menuconfig, it may appear and allow you to choose "Help" to show what depending option is missing preventing its selection.
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eborg
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PostPosted: Thu Dec 28, 2023 1:53 am    Post subject: Reply with quote

Thanks for that.
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n05ph3r42
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PostPosted: Wed Nov 27, 2024 6:25 pm    Post subject: Re: [Solved] Where is CONFIG_DEBUG_INFO_BTF? Reply with quote

eborg wrote:
I have a 6.1.67 kernel and am trying to work with libbpf which calls for a kernel built with CONFIG_DEBUG_INFO_BTF=y. A search in 'menuconfig' says the module is here ...

-> Kernel hacking
-> Compile-time checks and compiler options
-> Generate BTF typeinfo (DEBUG_INFO_BTF [=n])

But when I go there, I do not see the option. How else can I find a way to enable these options witin the kernel?


Hi,
Im interested in test of Extensible Scheduler Class, which requires this option too.
Am i correct, that option depends on CLANG as default C compiler? (CC_IS_CLANG)
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pietinger
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PostPosted: Wed Nov 27, 2024 8:48 pm    Post subject: Re: [Solved] Where is CONFIG_DEBUG_INFO_BTF? Reply with quote

n05ph3r42 wrote:
Im interested in test of Extensible Scheduler Class, which requires this option too.
Am i correct, that option depends on CLANG as default C compiler? (CC_IS_CLANG)

Although the kernel documentation [1] does not mention it, ninja and clang are used here [2].

1) https://www.kernel.org/doc/html/next/scheduler/sched-ext.html
2) https://speakerdeck.com/shun159/learning-sched-ext-bpf-extensible-scheduler-class
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GDH-gentoo
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PostPosted: Thu Nov 28, 2024 3:10 am    Post subject: Re: [Solved] Where is CONFIG_DEBUG_INFO_BTF? Reply with quote

n05ph3r42 wrote:
Im interested in test of Extensible Scheduler Class, which requires this option too.
Am i correct, that option depends on CLANG as default C compiler? (CC_IS_CLANG)

I don't think that you need to build the kernel with Clang (CC_IS_CLANG=y), but it seems that you do need Clang for creating BPF programs.

According to the README.md file in tools/sched_ext/ for version 6.12.1:

Quote:
Compiling the examples

There are a few toolchain dependencies for compiling the example schedulers.

Toolchain dependencies

1. clang >= 16.0.0

The schedulers are BPF programs, and therefore must be compiled with clang. gcc is actively working on adding a BPF backend compiler as well, but are still missing some features such as BTF type tags which are necessary for using kptrs.

And the makefile uses this recipe for compiling *.bpf.c files:

Code:
$(SCXOBJ_DIR)/%.bpf.o: %.bpf.c $(INCLUDE_DIR)/vmlinux.h include/scx/*.h      \
             | $(BPFOBJ) $(SCXOBJ_DIR)
   $(call msg,CLNG-BPF,,$(notdir $@))
   $(Q)$(CLANG) $(BPF_CFLAGS) -target bpf -c $< -o $@

That is, clang -target bpf -c.
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