linux-kernel - [PATCH] ARM: Do not select ARCH_HAS_KERNEL_FPU

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Message-ID: <20240509013727.648600-1-samuel.holland@sifive.com>
Date: Wed,  8 May 2024 18:37:10 -0700
From: Samuel Holland <samuel.holland@...ive.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
	linux-arm-kernel@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org,
	Samuel Holland <samuel.holland@...ive.com>,
	Thiago Jung Bauermann <thiago.bauermann@...aro.org>,
	kernel test robot <lkp@...el.com>,
	Ard Biesheuvel <ardb@...nel.org>,
	Andrew Davis <afd@...com>,
	Arnd Bergmann <arnd@...db.de>,
	Christian König <christian.koenig@....com>,
	Eric DeVolder <eric.devolder@...cle.com>,
	Rob Herring <robh@...nel.org>,
	Russell King <linux@...linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH] ARM: Do not select ARCH_HAS_KERNEL_FPU_SUPPORT

On 32-bit ARM, conversions between `double` and `long long` require
runtime library support. Since the kernel does not currently provide
this library support, the amdgpu driver fails to build:

  ERROR: modpost: "__aeabi_l2d" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko] undefined!
  ERROR: modpost: "__aeabi_d2ulz" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko] undefined!

As Arnd reports, there are likely no 32-bit ARM platforms which can use
the amdgpu driver anyway, due to lack of features like 64-bit
prefetchable BARs. Since amdgpu is currently the only real user of
ARCH_HAS_KERNEL_FPU_SUPPORT, drop support for this option instead of
bothering to implement the library functions.

Fixes: 12624fe2d707 ("ARM: implement ARCH_HAS_KERNEL_FPU_SUPPORT")
Reported-by: Thiago Jung Bauermann <thiago.bauermann@...aro.org>
Closes: https://lore.kernel.org/lkml/87wmp4oo3y.fsf@linaro.org/
Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202404042327.jRpt81kP-lkp@intel.com/
Suggested-by: Ard Biesheuvel <ardb@...nel.org>
Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
---

 arch/arm/Kconfig | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index b1751c2cab87..b14aed3a17ab 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -15,7 +15,6 @@ config ARM
 	select ARCH_HAS_FORTIFY_SOURCE
 	select ARCH_HAS_KEEPINITRD
 	select ARCH_HAS_KCOV
-	select ARCH_HAS_KERNEL_FPU_SUPPORT if KERNEL_MODE_NEON
 	select ARCH_HAS_MEMBARRIER_SYNC_CORE
 	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
 	select ARCH_HAS_PTE_SPECIAL if ARM_LPAE
-- 
2.44.0