linux/tools/include/nolibc/arch-arm.h

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/* SPDX-License-Identifier: LGPL-2.1 OR MIT */
/*
* ARM specific definitions for NOLIBC
* Copyright (C) 2017-2022 Willy Tarreau <w@1wt.eu>
*/
#ifndef _NOLIBC_ARCH_ARM_H
#define _NOLIBC_ARCH_ARM_H
#include "compiler.h"
#include "crt.h"
/* Syscalls for ARM in ARM or Thumb modes :
* - registers are 32-bit
* - stack is 8-byte aligned
* ( http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.faqs/ka4127.html)
* - syscall number is passed in r7
* - arguments are in r0, r1, r2, r3, r4, r5
* - the system call is performed by calling svc #0
* - syscall return comes in r0.
* - only lr is clobbered.
* - the arguments are cast to long and assigned into the target registers
* which are then simply passed as registers to the asm code, so that we
* don't have to experience issues with register constraints.
* - the syscall number is always specified last in order to allow to force
* some registers before (gcc refuses a %-register at the last position).
* - in thumb mode without -fomit-frame-pointer, r7 is also used to store the
* frame pointer, and we cannot directly assign it as a register variable,
* nor can we clobber it. Instead we assign the r6 register and swap it
* with r7 before calling svc, and r6 is marked as clobbered.
* We're just using any regular register which we assign to r7 after saving
* it.
*
* Also, ARM supports the old_select syscall if newselect is not available
*/
#define __ARCH_WANT_SYS_OLD_SELECT
#if (defined(__THUMBEB__) || defined(__THUMBEL__)) && \
!defined(NOLIBC_OMIT_FRAME_POINTER)
/* swap r6,r7 needed in Thumb mode since we can't use nor clobber r7 */
#define _NOLIBC_SYSCALL_REG "r6"
#define _NOLIBC_THUMB_SET_R7 "eor r7, r6\neor r6, r7\neor r7, r6\n"
#define _NOLIBC_THUMB_RESTORE_R7 "mov r7, r6\n"
#else /* we're in ARM mode */
/* in Arm mode we can directly use r7 */
#define _NOLIBC_SYSCALL_REG "r7"
#define _NOLIBC_THUMB_SET_R7 ""
#define _NOLIBC_THUMB_RESTORE_R7 ""
#endif /* end THUMB */
#define my_syscall0(num) \
({ \
register long _num __asm__(_NOLIBC_SYSCALL_REG) = (num); \
register long _arg1 __asm__ ("r0"); \
\
__asm__ volatile ( \
_NOLIBC_THUMB_SET_R7 \
"svc #0\n" \
_NOLIBC_THUMB_RESTORE_R7 \
: "=r"(_arg1), "=r"(_num) \
: "r"(_arg1), \
"r"(_num) \
: "memory", "cc", "lr" \
); \
_arg1; \
})
#define my_syscall1(num, arg1) \
({ \
register long _num __asm__(_NOLIBC_SYSCALL_REG) = (num); \
register long _arg1 __asm__ ("r0") = (long)(arg1); \
\
__asm__ volatile ( \
_NOLIBC_THUMB_SET_R7 \
"svc #0\n" \
_NOLIBC_THUMB_RESTORE_R7 \
: "=r"(_arg1), "=r" (_num) \
: "r"(_arg1), \
"r"(_num) \
: "memory", "cc", "lr" \
); \
_arg1; \
})
#define my_syscall2(num, arg1, arg2) \
({ \
register long _num __asm__(_NOLIBC_SYSCALL_REG) = (num); \
register long _arg1 __asm__ ("r0") = (long)(arg1); \
register long _arg2 __asm__ ("r1") = (long)(arg2); \
\
__asm__ volatile ( \
_NOLIBC_THUMB_SET_R7 \
"svc #0\n" \
_NOLIBC_THUMB_RESTORE_R7 \
: "=r"(_arg1), "=r" (_num) \
: "r"(_arg1), "r"(_arg2), \
"r"(_num) \
: "memory", "cc", "lr" \
); \
_arg1; \
})
#define my_syscall3(num, arg1, arg2, arg3) \
({ \
register long _num __asm__(_NOLIBC_SYSCALL_REG) = (num); \
register long _arg1 __asm__ ("r0") = (long)(arg1); \
register long _arg2 __asm__ ("r1") = (long)(arg2); \
register long _arg3 __asm__ ("r2") = (long)(arg3); \
\
__asm__ volatile ( \
_NOLIBC_THUMB_SET_R7 \
"svc #0\n" \
_NOLIBC_THUMB_RESTORE_R7 \
: "=r"(_arg1), "=r" (_num) \
: "r"(_arg1), "r"(_arg2), "r"(_arg3), \
"r"(_num) \
: "memory", "cc", "lr" \
); \
_arg1; \
})
#define my_syscall4(num, arg1, arg2, arg3, arg4) \
({ \
register long _num __asm__(_NOLIBC_SYSCALL_REG) = (num); \
register long _arg1 __asm__ ("r0") = (long)(arg1); \
register long _arg2 __asm__ ("r1") = (long)(arg2); \
register long _arg3 __asm__ ("r2") = (long)(arg3); \
register long _arg4 __asm__ ("r3") = (long)(arg4); \
\
__asm__ volatile ( \
_NOLIBC_THUMB_SET_R7 \
"svc #0\n" \
_NOLIBC_THUMB_RESTORE_R7 \
: "=r"(_arg1), "=r" (_num) \
: "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4), \
"r"(_num) \
: "memory", "cc", "lr" \
); \
_arg1; \
})
#define my_syscall5(num, arg1, arg2, arg3, arg4, arg5) \
({ \
register long _num __asm__(_NOLIBC_SYSCALL_REG) = (num); \
register long _arg1 __asm__ ("r0") = (long)(arg1); \
register long _arg2 __asm__ ("r1") = (long)(arg2); \
register long _arg3 __asm__ ("r2") = (long)(arg3); \
register long _arg4 __asm__ ("r3") = (long)(arg4); \
register long _arg5 __asm__ ("r4") = (long)(arg5); \
\
__asm__ volatile ( \
_NOLIBC_THUMB_SET_R7 \
"svc #0\n" \
_NOLIBC_THUMB_RESTORE_R7 \
: "=r"(_arg1), "=r" (_num) \
: "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4), "r"(_arg5), \
"r"(_num) \
: "memory", "cc", "lr" \
); \
_arg1; \
})
#define my_syscall6(num, arg1, arg2, arg3, arg4, arg5, arg6) \
({ \
register long _num __asm__(_NOLIBC_SYSCALL_REG) = (num); \
register long _arg1 __asm__ ("r0") = (long)(arg1); \
register long _arg2 __asm__ ("r1") = (long)(arg2); \
register long _arg3 __asm__ ("r2") = (long)(arg3); \
register long _arg4 __asm__ ("r3") = (long)(arg4); \
register long _arg5 __asm__ ("r4") = (long)(arg5); \
register long _arg6 __asm__ ("r5") = (long)(arg6); \
\
__asm__ volatile ( \
_NOLIBC_THUMB_SET_R7 \
"svc #0\n" \
_NOLIBC_THUMB_RESTORE_R7 \
: "=r"(_arg1), "=r" (_num) \
: "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4), "r"(_arg5), \
"r"(_arg6), "r"(_num) \
: "memory", "cc", "lr" \
); \
_arg1; \
})
/* startup code */
void __attribute__((weak, noreturn, optimize("Os", "omit-frame-pointer"))) __no_stack_protector _start(void)
tools/nolibc: make compiler and assembler agree on the section around _start The out-of-block asm() statement carrying _start does not allow the compiler to know what section the assembly code is being emitted to, and there's no easy way to push/pop the current section and restore it. It sometimes causes issues depending on the include files ordering and compiler optimizations. For example if a variable is declared immediately before the asm() block and another one after, the compiler assumes that the current section is still .bss and doesn't re-emit it, making the second variable appear inside the .text section instead. Forcing .bss at the end of the _start block doesn't work either because at certain optimizations the compiler may reorder blocks and will make some real code appear just after this block. A significant number of solutions were attempted, but many of them were still sensitive to section reordering. In the end, the best way to make sure the compiler and assembler agree on the current section is to place this code inside a function. Here the function is directly called _start and configured not to emit a frame-pointer, hence to have no prologue. If some future architectures would still emit some prologue, another working approach consists in naming the function differently and placing the _start label inside the asm statement. But the current solution is simpler. It was tested with nolibc-test at -O,-O0,-O2,-O3,-Os for arm,arm64,i386, mips,riscv,s390 and x86_64. Signed-off-by: Willy Tarreau <w@1wt.eu> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2023-01-10 08:24:13 +01:00
{
__asm__ volatile (
"mov %r0, sp\n" /* save stack pointer to %r0, as arg1 of _start_c */
"and ip, %r0, #-8\n" /* sp must be 8-byte aligned in the callee */
"mov sp, ip\n"
"bl _start_c\n" /* transfer to c runtime */
);
tools/nolibc: make compiler and assembler agree on the section around _start The out-of-block asm() statement carrying _start does not allow the compiler to know what section the assembly code is being emitted to, and there's no easy way to push/pop the current section and restore it. It sometimes causes issues depending on the include files ordering and compiler optimizations. For example if a variable is declared immediately before the asm() block and another one after, the compiler assumes that the current section is still .bss and doesn't re-emit it, making the second variable appear inside the .text section instead. Forcing .bss at the end of the _start block doesn't work either because at certain optimizations the compiler may reorder blocks and will make some real code appear just after this block. A significant number of solutions were attempted, but many of them were still sensitive to section reordering. In the end, the best way to make sure the compiler and assembler agree on the current section is to place this code inside a function. Here the function is directly called _start and configured not to emit a frame-pointer, hence to have no prologue. If some future architectures would still emit some prologue, another working approach consists in naming the function differently and placing the _start label inside the asm statement. But the current solution is simpler. It was tested with nolibc-test at -O,-O0,-O2,-O3,-Os for arm,arm64,i386, mips,riscv,s390 and x86_64. Signed-off-by: Willy Tarreau <w@1wt.eu> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2023-01-10 08:24:13 +01:00
__builtin_unreachable();
}
#endif /* _NOLIBC_ARCH_ARM_H */