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 [**]
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.)
14 [*] In the frame-pointers case rbp is fixed to the stack frame.
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.
24 For 32-bit we have the following conventions - kernel is built with
25 -mregparm=3 and -freg-struct-return:
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 [**]
34 ( here too esp is obviously invariant across normal function calls. eflags
35 is clobbered. Leftover arguments are passed over the stack frame. )
37 [*] In the frame-pointers case ebp is fixed to the stack frame.
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.
49 #include <asm/dwarf2.h>
54 * 64-bit system call stack frame layout defines and helpers,
65 /* arguments: interrupts/non tracing syscalls only save up to here: */
75 #define ORIG_RAX 120 /* + error_code */
76 /* end of arguments */
78 /* cpu exception frame or undefined in case of fast syscall: */
86 #define SWFRAME ORIG_RAX
88 .macro SAVE_ARGS addskip=0, save_rcx=1, save_r891011=1
89 subq $9*8+\addskip, %rsp
90 CFI_ADJUST_CFA_OFFSET 9*8+\addskip
110 #define ARG_SKIP (9*8)
112 .macro RESTORE_ARGS rstor_rax=1, addskip=0, rstor_rcx=1, rstor_r11=1, \
113 rstor_r8910=1, rstor_rdx=1
115 movq_cfi_restore 0*8, r11
119 movq_cfi_restore 1*8, r10
120 movq_cfi_restore 2*8, r9
121 movq_cfi_restore 3*8, r8
125 movq_cfi_restore 4*8, rax
129 movq_cfi_restore 5*8, rcx
133 movq_cfi_restore 6*8, rdx
136 movq_cfi_restore 7*8, rsi
137 movq_cfi_restore 8*8, rdi
139 .if ARG_SKIP+\addskip > 0
140 addq $ARG_SKIP+\addskip, %rsp
141 CFI_ADJUST_CFA_OFFSET -(ARG_SKIP+\addskip)
145 .macro LOAD_ARGS offset, skiprax=0
146 movq \offset(%rsp), %r11
147 movq \offset+8(%rsp), %r10
148 movq \offset+16(%rsp), %r9
149 movq \offset+24(%rsp), %r8
150 movq \offset+40(%rsp), %rcx
151 movq \offset+48(%rsp), %rdx
152 movq \offset+56(%rsp), %rsi
153 movq \offset+64(%rsp), %rdi
156 movq \offset+72(%rsp), %rax
160 #define REST_SKIP (6*8)
163 subq $REST_SKIP, %rsp
164 CFI_ADJUST_CFA_OFFSET REST_SKIP
174 movq_cfi_restore 0*8, r15
175 movq_cfi_restore 1*8, r14
176 movq_cfi_restore 2*8, r13
177 movq_cfi_restore 3*8, r12
178 movq_cfi_restore 4*8, rbp
179 movq_cfi_restore 5*8, rbx
180 addq $REST_SKIP, %rsp
181 CFI_ADJUST_CFA_OFFSET -(REST_SKIP)
189 .macro RESTORE_ALL addskip=0
191 RESTORE_ARGS 1, \addskip
198 #else /* CONFIG_X86_64 */
201 * For 32bit only simplified versions of SAVE_ALL/RESTORE_ALL. These
202 * are different from the entry_32.S versions in not changing the segment
203 * registers. So only suitable for in kernel use, not when transitioning
204 * from or to user space. The resulting stack frame is not a standard
205 * pt_regs frame. The main use case is calling C code from assembler
206 * when all the registers need to be preserved.
211 CFI_REL_OFFSET eax, 0
213 CFI_REL_OFFSET ebp, 0
215 CFI_REL_OFFSET edi, 0
217 CFI_REL_OFFSET esi, 0
219 CFI_REL_OFFSET edx, 0
221 CFI_REL_OFFSET ecx, 0
223 CFI_REL_OFFSET ebx, 0
243 #endif /* CONFIG_X86_64 */