1 /* SPDX-License-Identifier: LGPL-2.1 OR MIT */ 2 /* 3 * ARM specific definitions for NOLIBC 4 * Copyright (C) 2017-2022 Willy Tarreau <w@1wt.eu> 5 */ 6 7 #ifndef _NOLIBC_ARCH_ARM_H 8 #define _NOLIBC_ARCH_ARM_H 9 10 #include "compiler.h" 11 #include "crt.h" 12 13 /* Syscalls for ARM in ARM or Thumb modes : 14 * - registers are 32-bit 15 * - stack is 8-byte aligned 16 * ( http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.faqs/ka4127.html) 17 * - syscall number is passed in r7 18 * - arguments are in r0, r1, r2, r3, r4, r5 19 * - the system call is performed by calling svc #0 20 * - syscall return comes in r0. 21 * - only lr is clobbered. 22 * - the arguments are cast to long and assigned into the target registers 23 * which are then simply passed as registers to the asm code, so that we 24 * don't have to experience issues with register constraints. 25 * - the syscall number is always specified last in order to allow to force 26 * some registers before (gcc refuses a %-register at the last position). 27 * - in thumb mode without -fomit-frame-pointer, r7 is also used to store the 28 * frame pointer, and we cannot directly assign it as a register variable, 29 * nor can we clobber it. Instead we assign the r6 register and swap it 30 * with r7 before calling svc, and r6 is marked as clobbered. 31 * We're just using any regular register which we assign to r7 after saving 32 * it. 33 * 34 * Also, ARM supports the old_select syscall if newselect is not available 35 */ 36 #define __ARCH_WANT_SYS_OLD_SELECT 37 38 #if (defined(__THUMBEB__) || defined(__THUMBEL__)) && \ 39 !defined(NOLIBC_OMIT_FRAME_POINTER) 40 /* swap r6,r7 needed in Thumb mode since we can't use nor clobber r7 */ 41 #define _NOLIBC_SYSCALL_REG "r6" 42 #define _NOLIBC_THUMB_SET_R7 "eor r7, r6\neor r6, r7\neor r7, r6\n" 43 #define _NOLIBC_THUMB_RESTORE_R7 "mov r7, r6\n" 44 45 #else /* we're in ARM mode */ 46 /* in Arm mode we can directly use r7 */ 47 #define _NOLIBC_SYSCALL_REG "r7" 48 #define _NOLIBC_THUMB_SET_R7 "" 49 #define _NOLIBC_THUMB_RESTORE_R7 "" 50 51 #endif /* end THUMB */ 52 53 #define my_syscall0(num) \ 54 ({ \ 55 register long _num __asm__(_NOLIBC_SYSCALL_REG) = (num); \ 56 register long _arg1 __asm__ ("r0"); \ 57 \ 58 __asm__ volatile ( \ 59 _NOLIBC_THUMB_SET_R7 \ 60 "svc #0\n" \ 61 _NOLIBC_THUMB_RESTORE_R7 \ 62 : "=r"(_arg1), "=r"(_num) \ 63 : "r"(_arg1), \ 64 "r"(_num) \ 65 : "memory", "cc", "lr" \ 66 ); \ 67 _arg1; \ 68 }) 69 70 #define my_syscall1(num, arg1) \ 71 ({ \ 72 register long _num __asm__(_NOLIBC_SYSCALL_REG) = (num); \ 73 register long _arg1 __asm__ ("r0") = (long)(arg1); \ 74 \ 75 __asm__ volatile ( \ 76 _NOLIBC_THUMB_SET_R7 \ 77 "svc #0\n" \ 78 _NOLIBC_THUMB_RESTORE_R7 \ 79 : "=r"(_arg1), "=r" (_num) \ 80 : "r"(_arg1), \ 81 "r"(_num) \ 82 : "memory", "cc", "lr" \ 83 ); \ 84 _arg1; \ 85 }) 86 87 #define my_syscall2(num, arg1, arg2) \ 88 ({ \ 89 register long _num __asm__(_NOLIBC_SYSCALL_REG) = (num); \ 90 register long _arg1 __asm__ ("r0") = (long)(arg1); \ 91 register long _arg2 __asm__ ("r1") = (long)(arg2); \ 92 \ 93 __asm__ volatile ( \ 94 _NOLIBC_THUMB_SET_R7 \ 95 "svc #0\n" \ 96 _NOLIBC_THUMB_RESTORE_R7 \ 97 : "=r"(_arg1), "=r" (_num) \ 98 : "r"(_arg1), "r"(_arg2), \ 99 "r"(_num) \ 100 : "memory", "cc", "lr" \ 101 ); \ 102 _arg1; \ 103 }) 104 105 #define my_syscall3(num, arg1, arg2, arg3) \ 106 ({ \ 107 register long _num __asm__(_NOLIBC_SYSCALL_REG) = (num); \ 108 register long _arg1 __asm__ ("r0") = (long)(arg1); \ 109 register long _arg2 __asm__ ("r1") = (long)(arg2); \ 110 register long _arg3 __asm__ ("r2") = (long)(arg3); \ 111 \ 112 __asm__ volatile ( \ 113 _NOLIBC_THUMB_SET_R7 \ 114 "svc #0\n" \ 115 _NOLIBC_THUMB_RESTORE_R7 \ 116 : "=r"(_arg1), "=r" (_num) \ 117 : "r"(_arg1), "r"(_arg2), "r"(_arg3), \ 118 "r"(_num) \ 119 : "memory", "cc", "lr" \ 120 ); \ 121 _arg1; \ 122 }) 123 124 #define my_syscall4(num, arg1, arg2, arg3, arg4) \ 125 ({ \ 126 register long _num __asm__(_NOLIBC_SYSCALL_REG) = (num); \ 127 register long _arg1 __asm__ ("r0") = (long)(arg1); \ 128 register long _arg2 __asm__ ("r1") = (long)(arg2); \ 129 register long _arg3 __asm__ ("r2") = (long)(arg3); \ 130 register long _arg4 __asm__ ("r3") = (long)(arg4); \ 131 \ 132 __asm__ volatile ( \ 133 _NOLIBC_THUMB_SET_R7 \ 134 "svc #0\n" \ 135 _NOLIBC_THUMB_RESTORE_R7 \ 136 : "=r"(_arg1), "=r" (_num) \ 137 : "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4), \ 138 "r"(_num) \ 139 : "memory", "cc", "lr" \ 140 ); \ 141 _arg1; \ 142 }) 143 144 #define my_syscall5(num, arg1, arg2, arg3, arg4, arg5) \ 145 ({ \ 146 register long _num __asm__(_NOLIBC_SYSCALL_REG) = (num); \ 147 register long _arg1 __asm__ ("r0") = (long)(arg1); \ 148 register long _arg2 __asm__ ("r1") = (long)(arg2); \ 149 register long _arg3 __asm__ ("r2") = (long)(arg3); \ 150 register long _arg4 __asm__ ("r3") = (long)(arg4); \ 151 register long _arg5 __asm__ ("r4") = (long)(arg5); \ 152 \ 153 __asm__ volatile ( \ 154 _NOLIBC_THUMB_SET_R7 \ 155 "svc #0\n" \ 156 _NOLIBC_THUMB_RESTORE_R7 \ 157 : "=r"(_arg1), "=r" (_num) \ 158 : "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4), "r"(_arg5), \ 159 "r"(_num) \ 160 : "memory", "cc", "lr" \ 161 ); \ 162 _arg1; \ 163 }) 164 165 #define my_syscall6(num, arg1, arg2, arg3, arg4, arg5, arg6) \ 166 ({ \ 167 register long _num __asm__(_NOLIBC_SYSCALL_REG) = (num); \ 168 register long _arg1 __asm__ ("r0") = (long)(arg1); \ 169 register long _arg2 __asm__ ("r1") = (long)(arg2); \ 170 register long _arg3 __asm__ ("r2") = (long)(arg3); \ 171 register long _arg4 __asm__ ("r3") = (long)(arg4); \ 172 register long _arg5 __asm__ ("r4") = (long)(arg5); \ 173 register long _arg6 __asm__ ("r5") = (long)(arg6); \ 174 \ 175 __asm__ volatile ( \ 176 _NOLIBC_THUMB_SET_R7 \ 177 "svc #0\n" \ 178 _NOLIBC_THUMB_RESTORE_R7 \ 179 : "=r"(_arg1), "=r" (_num) \ 180 : "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4), "r"(_arg5), \ 181 "r"(_arg6), "r"(_num) \ 182 : "memory", "cc", "lr" \ 183 ); \ 184 _arg1; \ 185 }) 186 187 /* startup code */ 188 void __attribute__((weak, noreturn, optimize("Os", "omit-frame-pointer"))) __no_stack_protector _start(void) 189 { 190 __asm__ volatile ( 191 "mov %r0, sp\n" /* save stack pointer to %r0, as arg1 of _start_c */ 192 "and ip, %r0, #-8\n" /* sp must be 8-byte aligned in the callee */ 193 "mov sp, ip\n" 194 "bl _start_c\n" /* transfer to c runtime */ 195 ); 196 __builtin_unreachable(); 197 } 198 199 #endif /* _NOLIBC_ARCH_ARM_H */ 200