1/* Create new context.
2   Copyright (C) 2002-2021 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