1/* Create new context.
2 Copyright (C) 2002-2024 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19#include <sysdep.h>
20
21#define __ASSEMBLY__
22#include <asm/ptrace.h>
23#include "ucontext_i.h"
24#include <asm/errno.h>
25
26ENTRY (__makecontext)
27 CALL_MCOUNT 3
28 /* Save parameters into the parameter save area of callers frame. */
29 std r3,FRAME_PARM_SAVE+0(r1) /* ucontext_t *ucp */
30 std r4,FRAME_PARM_SAVE+8(r1) /* void (*func)(void) */
31 std r5,FRAME_PARM_SAVE+16(r1) /* int argc */
32 std r6,FRAME_PARM_SAVE+24(r1) /* ... */
33 std r7,FRAME_PARM_SAVE+32(r1)
34 std r8,FRAME_PARM_SAVE+40(r1)
35 std r9,FRAME_PARM_SAVE+48(r1)
36 std r10,FRAME_PARM_SAVE+56(r1)
37 mflr r0
38 /* Get the address of the target functions first parameter. */
39 addi r6,r1,FRAME_PARM_SAVE+24
40 std r0,FRAME_LR_SAVE(r1)
41 cfi_offset (lr, FRAME_LR_SAVE)
42 stdu r1,-128(r1)
43 cfi_adjust_cfa_offset (128)
44
45 /* Get the ucontexts stack pointer and size. Compute the top of stack
46 and round down to a quadword boundary. Then stack a dummy frame
47 with a null back chain. We store the context pointer in the frames
48 "compiler double word" field so we can recover if is the function
49 returns. Finally save the callers link register and TOC pointer
50 into this frame so the debugger can display a backtrace.
51 */
52 ld r7,UCONTEXT_STACK_SP(r3)
53 ld r0,UCONTEXT_STACK_SIZE(r3)
54 add r7,r7,r0
55 clrrdi r7,r7,4
56 li r0,0
57 stdu r0,-64(r7)
58 std r3,FRAME_PARM_SAVE(r7) /* Store context in dummy parm1. */
59 mflr r0
60 std r2,FRAME_TOC_SAVE(r7) /* Store the TOC pointer for later. */
61 std r0,FRAME_LR_SAVE(r7)
62
63 /* Now we need to stack another frame to hold the parameter save area
64 for the function. We need to allocate a frame with the minimum 48
65 byte header and 8 parameter register. However if there are more
66 than 8 parameters addition space is need to hold all the parameters.
67 The total size it rounded up to a quadword multiple then a frame is
68 stacked. This address is stored in the ucontext as GPR 1. */
69
70 cmpdi cr1,r5,8
71 sldi r8,r5,3
72 bgt cr1,L(gt8)
73 li r8,64
74L(gt8):
75 addi r8,r8,FRAME_PARM_SAVE+8 /* Add header plus rounding factor. */
76 clrrdi r8,r8,4 /* Round down to quadword. */
77
78 subf r8,r8,r7
79 std r7,0(r8) /* Stack the frame. */
80 std r8,(SIGCONTEXT_GP_REGS+(PT_R1*8))(r3)
81
82 /* Now we need to copy the target functions parameters. The functions
83 parameters are saved in the parameter save area. We skip over the
84 first three parameters and copy up to 8 double word into the
85 SIGCONTEXT_GP_REGS starting with R3. If there are more than 8
86 parameters then doublewords 8-N are copied into the parameter
87 save area of the context frame. */
88 cmpdi r5,0
89 beq L(noparms)
90 mr r0,r5
91 ble cr1,L(le8)
92 li r0,8
93L(le8):
94 mtctr r0
95 addi r7,r6,-8
96 addi r9,r3,(SIGCONTEXT_GP_REGS+(PT_R3*8)-8)
97L(parmloop2):
98 ldu r0,8(r7)
99 stdu r0,8(r9)
100 bdnz L(parmloop2)
101
102 addi r0,r5,-8
103 ble cr1,L(noparms)
104 mtctr r0
105 addi r9,r8,FRAME_PARM_SAVE+64-8
106L(parmloop):
107 ldu r0,8(r7)
108 stdu r0,8(r9)
109 bdnz L(parmloop)
110
111L(noparms):
112
113#if _CALL_ELF != 2
114 /* Load the function address and TOC from the function descriptor
115 and store them in the ucontext as NIP and r2. Store the 3rd
116 field of the function descriptor into the ucontext as r11 in case
117 the calling language needs the "environment pointer". */
118 ld r0,0(r4)
119 ld r10,8(r4);
120 ld r9,16(r4);
121 std r0,(SIGCONTEXT_GP_REGS+(PT_NIP*8))(r3)
122 std r10,(SIGCONTEXT_GP_REGS+(PT_R2*8))(r3)
123 std r9,(SIGCONTEXT_GP_REGS+(PT_R11*8))(r3)
124#else
125 /* In the ELFv2 ABI, the function pointer is already the address.
126 Store it as NIP and r12 as required by the ABI. */
127 std r4,(SIGCONTEXT_GP_REGS+(PT_NIP*8))(r3)
128 std r4,(SIGCONTEXT_GP_REGS+(PT_R12*8))(r3)
129#endif
130
131 /* If the target function returns we need to do some cleanup. We use a
132 code trick to get the address of our cleanup function into the link
133 register. Do not add any code between here and L(exitcode).
134 Use this conditional form of branch and link to avoid destroying
135 the cpu link stack used to predict blr return addresses. */
136 bcl 20,31,L(gotexitcodeaddr);
137
138 /* End FDE now, because while executing on the context's stack
139 the unwind info would be wrong otherwise. */
140 cfi_endproc
141
142 /* This is the helper code which gets called if a function which
143 is registered with 'makecontext' returns. In this case we
144 have to install the context listed in the uc_link element of
145 the context 'makecontext' manipulated at the time of the
146 'makecontext' call. If the pointer is NULL the process must
147 terminate. */
148L(exitcode):
149 /* Recover the ucontext and TOC from the dummy frame. */
150 ld r1,FRAME_BACKCHAIN(r1) /* Unstack the parameter save area frame. */
151 ld r3,FRAME_PARM_SAVE(r1)
152 ld r2,FRAME_TOC_SAVE(r1)
153 ld r3,UCONTEXT_LINK(r3) /* Load the resume context. */
154 cmpdi r3,0
155 beq L(do_exit)
156 bl JUMPTARGET(__setcontext)
157 nop
158 /* If setcontext returns (which can happen if the syscall fails) we will
159 exit the program with error status (-1). */
160 li r3,-1
161L(do_exit):
162#ifdef SHARED
163 b JUMPTARGET (NOTOC (__GI_exit));
164#else
165 b JUMPTARGET(exit);
166 nop
167#endif
168 b L(do_exit)
169
170 /* Re-establish FDE for the rest of the actual makecontext routine. */
171 cfi_startproc
172 cfi_offset (lr, FRAME_LR_SAVE)
173 cfi_adjust_cfa_offset (128)
174
175 /* The address of the exit code is in the link register. Store the lr
176 in the ucontext as LNK so the target function will return to our
177 exit code. */
178L(gotexitcodeaddr):
179 mflr r0
180 std r0,(SIGCONTEXT_GP_REGS+(PT_LNK*8))(r3)
181 ld r0,128+FRAME_LR_SAVE(r1)
182 addi r1,r1,128
183 mtlr r0
184 blr
185END(__makecontext)
186
187weak_alias (__makecontext, makecontext)
188

source code of glibc/sysdeps/unix/sysv/linux/powerpc/powerpc64/makecontext.S