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,
58 /* The layout forms the "struct pt_regs" on the stack: */
60 * C ABI says these regs are callee-preserved. They aren't saved on kernel entry
61 * unless syscall needs a complete, fully filled "struct pt_regs".
69 /* These regs are callee-clobbered. Always saved on kernel entry. */
80 * On syscall entry, this is syscall#. On CPU exception, this is error code.
81 * On hw interrupt, it's IRQ number:
84 /* Return frame for iretq */
91 .macro ALLOC_PT_GPREGS_ON_STACK addskip
=0
92 subq $
15*8+\addskip
, %rsp
93 CFI_ADJUST_CFA_OFFSET
15*8+\addskip
96 .macro SAVE_C_REGS_HELPER offset
=0 rax
=1 rcx
=1 r8plus
=1
98 movq_cfi r11
, 6*8+\offset
99 movq_cfi r10
, 7*8+\offset
100 movq_cfi r9
, 8*8+\offset
101 movq_cfi r8
, 9*8+\offset
104 movq_cfi rax
, 10*8+\offset
107 movq_cfi rcx
, 11*8+\offset
109 movq_cfi rdx
, 12*8+\offset
110 movq_cfi rsi
, 13*8+\offset
111 movq_cfi rdi
, 14*8+\offset
113 .macro SAVE_C_REGS offset
=0
114 SAVE_C_REGS_HELPER \offset
, 1, 1, 1
116 .macro SAVE_C_REGS_EXCEPT_RAX_RCX offset
=0
117 SAVE_C_REGS_HELPER \offset
, 0, 0, 1
119 .macro SAVE_C_REGS_EXCEPT_R891011
120 SAVE_C_REGS_HELPER
0, 1, 1, 0
122 .macro SAVE_C_REGS_EXCEPT_RCX_R891011
123 SAVE_C_REGS_HELPER
0, 1, 0, 0
126 .macro SAVE_EXTRA_REGS offset
=0
127 movq_cfi r15
, 0*8+\offset
128 movq_cfi r14
, 1*8+\offset
129 movq_cfi r13
, 2*8+\offset
130 movq_cfi r12
, 3*8+\offset
131 movq_cfi rbp
, 4*8+\offset
132 movq_cfi rbx
, 5*8+\offset
134 .macro SAVE_EXTRA_REGS_RBP offset
=0
135 movq_cfi rbp
, 4*8+\offset
138 .macro RESTORE_EXTRA_REGS offset
=0
139 movq_cfi_restore
0*8+\offset
, r15
140 movq_cfi_restore
1*8+\offset
, r14
141 movq_cfi_restore
2*8+\offset
, r13
142 movq_cfi_restore
3*8+\offset
, r12
143 movq_cfi_restore
4*8+\offset
, rbp
144 movq_cfi_restore
5*8+\offset
, rbx
147 .macro RESTORE_C_REGS_HELPER rstor_rax
=1, rstor_rcx
=1, rstor_r11
=1, rstor_r8910
=1, rstor_rdx
=1
149 movq_cfi_restore
6*8, r11
152 movq_cfi_restore
7*8, r10
153 movq_cfi_restore
8*8, r9
154 movq_cfi_restore
9*8, r8
157 movq_cfi_restore
10*8, rax
160 movq_cfi_restore
11*8, rcx
163 movq_cfi_restore
12*8, rdx
165 movq_cfi_restore
13*8, rsi
166 movq_cfi_restore
14*8, rdi
168 .macro RESTORE_C_REGS
169 RESTORE_C_REGS_HELPER
1,1,1,1,1
171 .macro RESTORE_C_REGS_EXCEPT_RAX
172 RESTORE_C_REGS_HELPER
0,1,1,1,1
174 .macro RESTORE_C_REGS_EXCEPT_RCX
175 RESTORE_C_REGS_HELPER
1,0,1,1,1
177 .macro RESTORE_RSI_RDI
178 RESTORE_C_REGS_HELPER
0,0,0,0,0
180 .macro RESTORE_RSI_RDI_RDX
181 RESTORE_C_REGS_HELPER
0,0,0,0,1
184 .macro REMOVE_PT_GPREGS_FROM_STACK addskip
=0
185 addq $
15*8+\addskip
, %rsp
186 CFI_ADJUST_CFA_OFFSET
-(15*8+\addskip
)
193 #else /* CONFIG_X86_64 */
196 * For 32bit only simplified versions of SAVE_ALL/RESTORE_ALL. These
197 * are different from the entry_32.S versions in not changing the segment
198 * registers. So only suitable for in kernel use, not when transitioning
199 * from or to user space. The resulting stack frame is not a standard
200 * pt_regs frame. The main use case is calling C code from assembler
201 * when all the registers need to be preserved.
224 #endif /* CONFIG_X86_64 */