Switching stacks in C requires inline assembly inside a naked function and even then, the compiler is free to keep using the old stack pointer.
Let's add call_with_stack() instead, which takes the new stack top, a function and two arguments for it. Everything is passed in registers, so it's safe to call before a stack has been set up, as the upcoming PBL stage dispatch will do. The prototype goes into asm-generic/registers.h, as other architectures will implement the same helper. Assisted-by: Claude:fable-5 Signed-off-by: Ahmad Fatoum <[email protected]> --- arch/riscv/lib/Makefile | 1 + arch/riscv/lib/call_with_stack.S | 12 ++++++++++++ include/asm-generic/registers.h | 10 ++++++++++ 3 files changed, 23 insertions(+) create mode 100644 arch/riscv/lib/call_with_stack.S diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile index 693248080070..13c7c34a487c 100644 --- a/arch/riscv/lib/Makefile +++ b/arch/riscv/lib/Makefile @@ -4,6 +4,7 @@ extra-y += barebox.lds obj-y += dtb.o obj-pbl-y += sections.o setupc.o reloc.o sections.o runtime-offset.o +obj-pbl-y += call_with_stack.o obj-$(CONFIG_ARCH_HAS_SJLJ) += setjmp.o longjmp.o obj-$(CONFIG_RISCV_OPTIMZED_STRING_FUNCTIONS) += memcpy.o memset.o memmove.o obj-$(CONFIG_RISCV_SBI) += sbi.o diff --git a/arch/riscv/lib/call_with_stack.S b/arch/riscv/lib/call_with_stack.S new file mode 100644 index 000000000000..f3093d062a59 --- /dev/null +++ b/arch/riscv/lib/call_with_stack.S @@ -0,0 +1,12 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ + +#include <linux/linkage.h> + +.section .text.call_with_stack +ENTRY(call_with_stack) + mv t1, a1 + mv sp, a0 + mv a0, a2 + mv a1, a3 + jr t1 +ENDPROC(call_with_stack) diff --git a/include/asm-generic/registers.h b/include/asm-generic/registers.h index 8ce28f74e1db..ec85476019c7 100644 --- a/include/asm-generic/registers.h +++ b/include/asm-generic/registers.h @@ -20,4 +20,14 @@ static __always_inline bool pc_inside(unsigned long start, unsigned long size) return pc - start < size; } +/* + * call_with_stack - switch to the stack ending at stack_top and call fn + * + * stack_top must be aligned as the architecture requires and fn must not + * return. No memory is accessed, so there needn't be a stack yet. + */ +void __noreturn call_with_stack(unsigned long stack_top, + void (*fn)(unsigned long, unsigned long), + unsigned long arg0, unsigned long arg1); + #endif -- 2.47.3
