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[libc] Enable the FPU in Arm startup code (#166349)

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This patch enables the FPU in Arm startup code, which is required to run
tests on Arm configurations with hardware floating-point support.
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Victor Campos 2025-11-06 10:45:45 +00:00 committed by GitHub
parent 06ec47055a
commit 22b6c491d6
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26
libc/startup/baremetal/arm/start.cpp
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@ -131,6 +131,32 @@ namespace LIBC_NAMESPACE_DECL {
__arm_wsr("CPSR_c", 0x13); // SVC
#endif
#ifdef __ARM_FP
// Enable FPU
#if __ARM_ARCH_PROFILE == 'M'
// Based on
// https://developer.arm.com/documentation/dui0646/c/Cortex-M7-Peripherals/Floating-Point-Unit/Enabling-the-FPU
// Set CPACR cp10 and cp11
auto cpacr = (volatile uint32_t *const)0xE000ED88;
*cpacr |= (0xF << 20);
__dsb(0xF);
__isb(0xF);
#elif __ARM_ARCH_PROFILE == 'A' || __ARM_ARCH_PROFILE == 'R'
// Based on
// https://developer.arm.com/documentation/dui0472/m/Compiler-Coding-Practices/Enabling-NEON-and-FPU-for-bare-metal
// Set CPACR cp10 and cp11
uint32_t cpacr = __arm_rsr("p15:0:c1:c0:2");
cpacr |= (0xF << 20);
__arm_wsr("p15:0:c1:c0:2", cpacr);
__isb(0xF);
// Set FPEXC.EN
uint32_t fpexc;
__asm__ __volatile__("vmrs %0, FPEXC" : "=r"(fpexc) : :);
fpexc |= (1 << 30);
__asm__ __volatile__("vmsr FPEXC, %0" : : "r"(fpexc) :);
#endif
#endif
// Perform the equivalent of scatterloading
LIBC_NAMESPACE::memcpy(__data_start, __data_source,
reinterpret_cast<uintptr_t>(__data_size));