github.com/sbinet/go@v0.0.0-20160827155028-54d7de7dd62b/src/runtime/tls_arm.s (about)

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