1 /* 2 3 x86 function call convention, 64-bit: 4 ------------------------------------- 5 arguments | callee-saved | extra caller-saved | return 6 [callee-clobbered] | | [callee-clobbered] | 7 --------------------------------------------------------------------------- 8 rdi rsi rdx rcx r8-9 | rbx rbp [*] r12-15 | r10-11 | rax, rdx [**] 9 10 ( rsp is obviously invariant across normal function calls. (gcc can 'merge' 11 functions when it sees tail-call optimization possibilities) rflags is 12 clobbered. Leftover arguments are passed over the stack frame.) 13 14 [*] In the frame-pointers case rbp is fixed to the stack frame. 15 16 [**] for struct return values wider than 64 bits the return convention is a 17 bit more complex: up to 128 bits width we return small structures 18 straight in rax, rdx. For structures larger than that (3 words or 19 larger) the caller puts a pointer to an on-stack return struct 20 [allocated in the caller's stack frame] into the first argument - i.e. 21 into rdi. All other arguments shift up by one in this case. 22 Fortunately this case is rare in the kernel. 23 24 For 32-bit we have the following conventions - kernel is built with 25 -mregparm=3 and -freg-struct-return: 26 27 x86 function calling convention, 32-bit: 28 ---------------------------------------- 29 arguments | callee-saved | extra caller-saved | return 30 [callee-clobbered] | | [callee-clobbered] | 31 ------------------------------------------------------------------------- 32 eax edx ecx | ebx edi esi ebp [*] | <none> | eax, edx [**] 33 34 ( here too esp is obviously invariant across normal function calls. eflags 35 is clobbered. Leftover arguments are passed over the stack frame. ) 36 37 [*] In the frame-pointers case ebp is fixed to the stack frame. 38 39 [**] We build with -freg-struct-return, which on 32-bit means similar 40 semantics as on 64-bit: edx can be used for a second return value 41 (i.e. covering integer and structure sizes up to 64 bits) - after that 42 it gets more complex and more expensive: 3-word or larger struct returns 43 get done in the caller's frame and the pointer to the return struct goes 44 into regparm0, i.e. eax - the other arguments shift up and the 45 function's register parameters degenerate to regparm=2 in essence. 46 47 */ 48 49 #ifdef CONFIG_X86_64 50 51 /* 52 * 64-bit system call stack frame layout defines and helpers, 53 * for assembly code: 54 */ 55 56 /* The layout forms the "struct pt_regs" on the stack: */ 57 /* 58 * C ABI says these regs are callee-preserved. They aren't saved on kernel entry 59 * unless syscall needs a complete, fully filled "struct pt_regs". 60 */ 61 #define R15 0*8 62 #define R14 1*8 63 #define R13 2*8 64 #define R12 3*8 65 #define RBP 4*8 66 #define RBX 5*8 67 /* These regs are callee-clobbered. Always saved on kernel entry. */ 68 #define R11 6*8 69 #define R10 7*8 70 #define R9 8*8 71 #define R8 9*8 72 #define RAX 10*8 73 #define RCX 11*8 74 #define RDX 12*8 75 #define RSI 13*8 76 #define RDI 14*8 77 /* 78 * On syscall entry, this is syscall#. On CPU exception, this is error code. 79 * On hw interrupt, it's IRQ number: 80 */ 81 #define ORIG_RAX 15*8 82 /* Return frame for iretq */ 83 #define RIP 16*8 84 #define CS 17*8 85 #define EFLAGS 18*8 86 #define RSP 19*8 87 #define SS 20*8 88 89 #define SIZEOF_PTREGS 21*8 90 91 .macro ALLOC_PT_GPREGS_ON_STACK addskip=0 92 addq $-(15*8+\addskip), %rsp 93 .endm 94 95 .macro SAVE_C_REGS_HELPER offset=0 rax=1 rcx=1 r8910=1 r11=1 96 .if \r11 97 movq %r11, 6*8+\offset(%rsp) 98 .endif 99 .if \r8910 100 movq %r10, 7*8+\offset(%rsp) 101 movq %r9, 8*8+\offset(%rsp) 102 movq %r8, 9*8+\offset(%rsp) 103 .endif 104 .if \rax 105 movq %rax, 10*8+\offset(%rsp) 106 .endif 107 .if \rcx 108 movq %rcx, 11*8+\offset(%rsp) 109 .endif 110 movq %rdx, 12*8+\offset(%rsp) 111 movq %rsi, 13*8+\offset(%rsp) 112 movq %rdi, 14*8+\offset(%rsp) 113 .endm 114 .macro SAVE_C_REGS offset=0 115 SAVE_C_REGS_HELPER \offset, 1, 1, 1, 1 116 .endm 117 .macro SAVE_C_REGS_EXCEPT_RAX_RCX offset=0 118 SAVE_C_REGS_HELPER \offset, 0, 0, 1, 1 119 .endm 120 .macro SAVE_C_REGS_EXCEPT_R891011 121 SAVE_C_REGS_HELPER 0, 1, 1, 0, 0 122 .endm 123 .macro SAVE_C_REGS_EXCEPT_RCX_R891011 124 SAVE_C_REGS_HELPER 0, 1, 0, 0, 0 125 .endm 126 .macro SAVE_C_REGS_EXCEPT_RAX_RCX_R11 127 SAVE_C_REGS_HELPER 0, 0, 0, 1, 0 128 .endm 129 130 .macro SAVE_EXTRA_REGS offset=0 131 movq %r15, 0*8+\offset(%rsp) 132 movq %r14, 1*8+\offset(%rsp) 133 movq %r13, 2*8+\offset(%rsp) 134 movq %r12, 3*8+\offset(%rsp) 135 movq %rbp, 4*8+\offset(%rsp) 136 movq %rbx, 5*8+\offset(%rsp) 137 .endm 138 139 .macro RESTORE_EXTRA_REGS offset=0 140 movq 0*8+\offset(%rsp), %r15 141 movq 1*8+\offset(%rsp), %r14 142 movq 2*8+\offset(%rsp), %r13 143 movq 3*8+\offset(%rsp), %r12 144 movq 4*8+\offset(%rsp), %rbp 145 movq 5*8+\offset(%rsp), %rbx 146 .endm 147 148 .macro ZERO_EXTRA_REGS 149 xorl %r15d, %r15d 150 xorl %r14d, %r14d 151 xorl %r13d, %r13d 152 xorl %r12d, %r12d 153 xorl %ebp, %ebp 154 xorl %ebx, %ebx 155 .endm 156 157 .macro RESTORE_C_REGS_HELPER rstor_rax=1, rstor_rcx=1, rstor_r11=1, rstor_r8910=1, rstor_rdx=1 158 .if \rstor_r11 159 movq 6*8(%rsp), %r11 160 .endif 161 .if \rstor_r8910 162 movq 7*8(%rsp), %r10 163 movq 8*8(%rsp), %r9 164 movq 9*8(%rsp), %r8 165 .endif 166 .if \rstor_rax 167 movq 10*8(%rsp), %rax 168 .endif 169 .if \rstor_rcx 170 movq 11*8(%rsp), %rcx 171 .endif 172 .if \rstor_rdx 173 movq 12*8(%rsp), %rdx 174 .endif 175 movq 13*8(%rsp), %rsi 176 movq 14*8(%rsp), %rdi 177 .endm 178 .macro RESTORE_C_REGS 179 RESTORE_C_REGS_HELPER 1,1,1,1,1 180 .endm 181 .macro RESTORE_C_REGS_EXCEPT_RAX 182 RESTORE_C_REGS_HELPER 0,1,1,1,1 183 .endm 184 .macro RESTORE_C_REGS_EXCEPT_RCX 185 RESTORE_C_REGS_HELPER 1,0,1,1,1 186 .endm 187 .macro RESTORE_C_REGS_EXCEPT_R11 188 RESTORE_C_REGS_HELPER 1,1,0,1,1 189 .endm 190 .macro RESTORE_C_REGS_EXCEPT_RCX_R11 191 RESTORE_C_REGS_HELPER 1,0,0,1,1 192 .endm 193 194 .macro REMOVE_PT_GPREGS_FROM_STACK addskip=0 195 subq $-(15*8+\addskip), %rsp 196 .endm 197 198 .macro icebp 199 .byte 0xf1 200 .endm 201 202 #else /* CONFIG_X86_64 */ 203 204 /* 205 * For 32bit only simplified versions of SAVE_ALL/RESTORE_ALL. These 206 * are different from the entry_32.S versions in not changing the segment 207 * registers. So only suitable for in kernel use, not when transitioning 208 * from or to user space. The resulting stack frame is not a standard 209 * pt_regs frame. The main use case is calling C code from assembler 210 * when all the registers need to be preserved. 211 */ 212 213 .macro SAVE_ALL 214 pushl %eax 215 pushl %ebp 216 pushl %edi 217 pushl %esi 218 pushl %edx 219 pushl %ecx 220 pushl %ebx 221 .endm 222 223 .macro RESTORE_ALL 224 popl %ebx 225 popl %ecx 226 popl %edx 227 popl %esi 228 popl %edi 229 popl %ebp 230 popl %eax 231 .endm 232 233 #endif /* CONFIG_X86_64 */ 234 235