From 95ede670bcfea5ea22965962fe764841243eb864 Mon Sep 17 00:00:00 2001 From: Michael Brown Date: Sun, 11 May 2025 13:04:51 +0100 Subject: [riscv] Hold virtual address offset in the thread pointer register iPXE does not make use of any thread-local storage. Use the otherwise unused thread pointer register ("tp") to hold the current value of the virtual address offset, rather than using a global variable. This ensures that virt_offset can be made valid even during very early initialisation (when iPXE may be executing directly from read-only memory and so cannot update a global variable). Signed-off-by: Michael Brown --- src/arch/riscv/include/bits/virt_offset.h | 33 +++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+) create mode 100644 src/arch/riscv/include/bits/virt_offset.h (limited to 'src/arch/riscv/include') diff --git a/src/arch/riscv/include/bits/virt_offset.h b/src/arch/riscv/include/bits/virt_offset.h new file mode 100644 index 000000000..83ac17551 --- /dev/null +++ b/src/arch/riscv/include/bits/virt_offset.h @@ -0,0 +1,33 @@ +#ifndef _BITS_VIRT_OFFSET_H +#define _BITS_VIRT_OFFSET_H + +/** @file + * + * RISCV-specific virtual address offset + * + * We use the thread pointer register (tp) to hold the virtual address + * offset, so that virtual-to-physical address translations work as + * expected even while we are executing directly from read-only memory + * (and so cannot store a value in a global virt_offset variable). + * + */ + +FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL ); + +/** + * Read virtual address offset held in thread pointer register + * + * @ret virt_offset Virtual address offset + */ +static inline __attribute__ (( const, always_inline )) unsigned long +tp_virt_offset ( void ) { + register unsigned long tp asm ( "tp" ); + + __asm__ ( "" : "=r" ( tp ) ); + return tp; +} + +/** Always read thread pointer register to get virtual address offset */ +#define virt_offset tp_virt_offset() + +#endif /* _BITS_VIRT_OFFSET_H */ -- cgit v1.2.3-55-g7522