Text file src/runtime/tls_arm.s
1 // Copyright 2014 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
4
5 // +build !windows
6
7 #include "go_asm.h"
8 #include "go_tls.h"
9 #include "funcdata.h"
10 #include "textflag.h"
11
12 // We have to resort to TLS variable to save g(R10).
13 // One reason is that external code might trigger
14 // SIGSEGV, and our runtime.sigtramp don't even know we
15 // are in external code, and will continue to use R10,
16 // this might as well result in another SIGSEGV.
17 // Note: both functions will clobber R0 and R11 and
18 // can be called from 5c ABI code.
19
20 // On android and darwin, runtime.tls_g is a normal variable.
21 // TLS offset is computed in x_cgo_inittls.
22 #ifdef GOOS_android
23 #define TLSG_IS_VARIABLE
24 #endif
25 #ifdef GOOS_darwin
26 #define TLSG_IS_VARIABLE
27 #endif
28
29 // save_g saves the g register into pthread-provided
30 // thread-local memory, so that we can call externally compiled
31 // ARM code that will overwrite those registers.
32 // NOTE: runtime.gogo assumes that R1 is preserved by this function.
33 // runtime.mcall assumes this function only clobbers R0 and R11.
34 // Returns with g in R0.
35 TEXT runtime·save_g(SB),NOSPLIT|NOFRAME,$0
36 #ifdef GOOS_nacl
37 // nothing to do as nacl/arm does not use TLS at all.
38 MOVW g, R0 // preserve R0 across call to setg<>
39 RET
40 #else
41 // If the host does not support MRC the linker will replace it with
42 // a call to runtime.read_tls_fallback which jumps to __kuser_get_tls.
43 // The replacement function saves LR in R11 over the call to read_tls_fallback.
44 MRC 15, 0, R0, C13, C0, 3 // fetch TLS base pointer
45 BIC $3, R0 // Darwin/ARM might return unaligned pointer
46 MOVW runtime·tls_g(SB), R11
47 ADD R11, R0
48 MOVW g, 0(R0)
49 MOVW g, R0 // preserve R0 across call to setg<>
50 RET
51 #endif
52
53 // load_g loads the g register from pthread-provided
54 // thread-local memory, for use after calling externally compiled
55 // ARM code that overwrote those registers.
56 TEXT runtime·load_g(SB),NOSPLIT,$0
57 #ifdef GOOS_nacl
58 // nothing to do as nacl/arm does not use TLS at all.
59 RET
60 #else
61 // See save_g
62 MRC 15, 0, R0, C13, C0, 3 // fetch TLS base pointer
63 BIC $3, R0 // Darwin/ARM might return unaligned pointer
64 MOVW runtime·tls_g(SB), R11
65 ADD R11, R0
66 MOVW 0(R0), g
67 RET
68 #endif
69
70 // This is called from rt0_go, which runs on the system stack
71 // using the initial stack allocated by the OS.
72 // It calls back into standard C using the BL (R4) below.
73 // To do that, the stack pointer must be 8-byte-aligned
74 // on some systems, notably FreeBSD.
75 // The ARM ABI says the stack pointer must be 8-byte-aligned
76 // on entry to any function, but only FreeBSD's C library seems to care.
77 // The caller was 8-byte aligned, but we push an LR.
78 // Declare a dummy word ($4, not $0) to make sure the
79 // frame is 8 bytes and stays 8-byte-aligned.
80 TEXT runtime·_initcgo(SB),NOSPLIT,$4
81 #ifndef GOOS_nacl
82 // if there is an _cgo_init, call it.
83 MOVW _cgo_init(SB), R4
84 CMP $0, R4
85 B.EQ nocgo
86 MRC 15, 0, R0, C13, C0, 3 // load TLS base pointer
87 MOVW R0, R3 // arg 3: TLS base pointer
88 #ifdef TLSG_IS_VARIABLE
89 MOVW $runtime·tls_g(SB), R2 // arg 2: &tls_g
90 #else
91 MOVW $0, R2 // arg 2: not used when using platform tls
92 #endif
93 MOVW $setg_gcc<>(SB), R1 // arg 1: setg
94 MOVW g, R0 // arg 0: G
95 BL (R4) // will clobber R0-R3
96 #endif
97 nocgo:
98 RET
99
100 // void setg_gcc(G*); set g called from gcc.
101 TEXT setg_gcc<>(SB),NOSPLIT,$0
102 MOVW R0, g
103 B runtime·save_g(SB)
104
105 #ifdef TLSG_IS_VARIABLE
106 #ifdef GOOS_android
107 // Use the free TLS_SLOT_APP slot #2 on Android Q.
108 // Earlier androids are set up in gcc_android.c.
109 DATA runtime·tls_g+0(SB)/4, $8
110 #endif
111 GLOBL runtime·tls_g+0(SB), NOPTR, $4
112 #else
113 GLOBL runtime·tls_g+0(SB), TLSBSS, $4
114 #endif
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