github.com/rsc/go@v0.0.0-20150416155037-e040fd465409/src/runtime/tls_ppc64x.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  // +build ppc64 ppc64le
     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 (R30).
    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 R30,
    16  // this might well result in another SIGSEGV.
    17  
    18  // save_g saves the g register into pthread-provided
    19  // thread-local memory, so that we can call externally compiled
    20  // ppc64 code that will overwrite this register.
    21  //
    22  // If !iscgo, this is a no-op.
    23  //
    24  // NOTE: setg_gcc<> assume this clobbers only R31.
    25  TEXT runtime·save_g(SB),NOSPLIT,$-8-0
    26  	MOVB	runtime·iscgo(SB), R31
    27  	CMP	R31, $0
    28  	BEQ	nocgo
    29  
    30  	// $runtime.tlsg(SB) is a special linker symbol.
    31  	// It is the offset from the start of TLS to our
    32  	// thread-local storage for g.
    33  	MOVD	$runtime·tlsg(SB), R31
    34  	ADD	R13, R31
    35  	// The actual TLS base is 0x7000 below R13
    36  	SUB	$0x7000, R31
    37  
    38  	// Store g in TLS
    39  	MOVD	g, 0(R31)
    40  
    41  nocgo:
    42  	RET
    43  
    44  // load_g loads the g register from pthread-provided
    45  // thread-local memory, for use after calling externally compiled
    46  // ppc64 code that overwrote those registers.
    47  //
    48  // This is never called directly from C code (it doesn't have to
    49  // follow the C ABI), but it may be called from a C context, where the
    50  // usual Go registers aren't set up.
    51  //
    52  // NOTE: _cgo_topofstack assumes this only clobbers g (R30), and R31.
    53  TEXT runtime·load_g(SB),NOSPLIT,$-8-0
    54  	MOVD	$runtime·tlsg(SB), R31
    55  	// R13 is the C ABI TLS base pointer + 0x7000
    56  	ADD	R13, R31
    57  	SUB	$0x7000, R31
    58  
    59  	MOVD	0(R31), g
    60  	RET