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From: Alan Maguire <almagui@kernel.org>
To: Sasha Levin <sashal@kernel.org>, Vineet Gupta <vgupta@kernel.org>,
	linux-snps-arc@lists.infradead.org
Cc: Andrii Nakryiko <andrii@kernel.org>,
	Ilya Leoshkevich <iii@linux.ibm.com>,
	bpf@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] ARC: Strip libgcc debug information when generating BTF
Date: Fri, 16 Oct 2026 10:18:46 +0100	[thread overview]
Message-ID: <3683fce4-8700-4e6b-9a1d-86826348a5dc@kernel.org> (raw)
In-Reply-To: <20261015154044.4058618-1-sashal@kernel.org>

On 10/15/26 4:40 PM, Sasha Levin wrote:
> ARC links against the compiler's libgcc archive. The ARC GNU 2023.03
> toolchain ships this library with debug information, including complex
> floating-point types in integer arithmetic helpers such as __udivdi3.
> These types reach vmlinux even though the kernel does not use complex
> floating-point arithmetic.
> 
> When floating-point BTF encoding is enabled, pahole rejects those types:
> 
>   Complex, interval and imaginary float types are not supported
>   Error while encoding BTF.
>   FAILED: load BTF from .tmp_vmlinux1.BTF.1: No such file or directory
> 
> KernelCI's upgrade to pahole 1.31 exposed this long-standing problem as
> failed ARC builds. As of 1.32, pahole still rejects these types, and
> older versions will stay in use, so the kernel build has to keep them
> out of vmlinux. Commit f122668ddcce ("ARC: Add eBPF JIT support")
> documented the same failure along with a workaround of disabling
> floating-point BTF encoding, but that also discards supported
> floating-point types from kernel BTF.
> 
> For CONFIG_DEBUG_INFO_BTF, generate a debug-stripped copy of the selected
> libgcc archive in the output tree and link that copy. Preserve the archive
> structure so that only needed helpers are linked, and use the normal
> Kbuild objcopy rule to track input and command changes. The trade-off is
> that vmlinux in BTF-enabled builds no longer carries DWARF for the libgcc
> helpers. Debug information for kernel code, the installed toolchain and
> non-BTF builds stay unchanged.
> 
> Reproduced and tested with ARC GCC 12.2.1 and pahole 1.31 and 1.32 using
> an ARCv2 tinyconfig with BPF_SYSCALL and DWARF4/BTF enabled. Before and
> after vmlinux.o files are identical after stripping debug information.
> 
> Fixes: db16c1fe92d7 ("bpf: Generate BTF_KIND_FLOAT when linking vmlinux")
> Link: https://github.com/kernelci/kernelci-core/commit/e71b8c9f42253180596e734c18965a5aad80c8c5
> Signed-off-by: Sasha Levin <sashal@kernel.org>

Acked-by: Alan Maguire (Oracle) <almagui@kernel.org>

Thanks for the fix Sasha! More complete floating point representations for BTF
should definitely be on the to-do list..


WARNING: multiple messages have this Message-ID (diff)
From: Alan Maguire <almagui@kernel.org>
To: Sasha Levin <sashal@kernel.org>, Vineet Gupta <vgupta@kernel.org>,
	linux-snps-arc@lists.infradead.org
Cc: Andrii Nakryiko <andrii@kernel.org>,
	Ilya Leoshkevich <iii@linux.ibm.com>,
	bpf@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] ARC: Strip libgcc debug information when generating BTF
Date: Fri, 16 Oct 2026 10:18:46 +0100	[thread overview]
Message-ID: <3683fce4-8700-4e6b-9a1d-86826348a5dc@kernel.org> (raw)
In-Reply-To: <20261015154044.4058618-1-sashal@kernel.org>

On 10/15/26 4:40 PM, Sasha Levin wrote:
> ARC links against the compiler's libgcc archive. The ARC GNU 2023.03
> toolchain ships this library with debug information, including complex
> floating-point types in integer arithmetic helpers such as __udivdi3.
> These types reach vmlinux even though the kernel does not use complex
> floating-point arithmetic.
> 
> When floating-point BTF encoding is enabled, pahole rejects those types:
> 
>   Complex, interval and imaginary float types are not supported
>   Error while encoding BTF.
>   FAILED: load BTF from .tmp_vmlinux1.BTF.1: No such file or directory
> 
> KernelCI's upgrade to pahole 1.31 exposed this long-standing problem as
> failed ARC builds. As of 1.32, pahole still rejects these types, and
> older versions will stay in use, so the kernel build has to keep them
> out of vmlinux. Commit f122668ddcce ("ARC: Add eBPF JIT support")
> documented the same failure along with a workaround of disabling
> floating-point BTF encoding, but that also discards supported
> floating-point types from kernel BTF.
> 
> For CONFIG_DEBUG_INFO_BTF, generate a debug-stripped copy of the selected
> libgcc archive in the output tree and link that copy. Preserve the archive
> structure so that only needed helpers are linked, and use the normal
> Kbuild objcopy rule to track input and command changes. The trade-off is
> that vmlinux in BTF-enabled builds no longer carries DWARF for the libgcc
> helpers. Debug information for kernel code, the installed toolchain and
> non-BTF builds stay unchanged.
> 
> Reproduced and tested with ARC GCC 12.2.1 and pahole 1.31 and 1.32 using
> an ARCv2 tinyconfig with BPF_SYSCALL and DWARF4/BTF enabled. Before and
> after vmlinux.o files are identical after stripping debug information.
> 
> Fixes: db16c1fe92d7 ("bpf: Generate BTF_KIND_FLOAT when linking vmlinux")
> Link: https://github.com/kernelci/kernelci-core/commit/e71b8c9f42253180596e734c18965a5aad80c8c5
> Signed-off-by: Sasha Levin <sashal@kernel.org>

Acked-by: Alan Maguire (Oracle) <almagui@kernel.org>

Thanks for the fix Sasha! More complete floating point representations for BTF
should definitely be on the to-do list..


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  reply	other threads:[~2026-10-16  9:18 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-10-15 15:40 [PATCH] ARC: Strip libgcc debug information when generating BTF Sasha Levin
2026-10-15 15:40 ` Sasha Levin
2026-10-16  9:18 ` Alan Maguire [this message]
2026-10-16  9:18   ` Alan Maguire

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