tls_arm.s

Documentation: runtime

     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//go: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, 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
    26// save_g saves the g register into pthread-provided
    27// thread-local memory, so that we can call externally compiled
    28// ARM code that will overwrite those registers.
    29// NOTE: runtime.gogo assumes that R1 is preserved by this function.
    30//       runtime.mcall assumes this function only clobbers R0 and R11.
    31// Returns with g in R0.
    32TEXT runtime·save_g(SB),NOSPLIT,$0
    33	// If the host does not support MRC the linker will replace it with
    34	// a call to runtime.read_tls_fallback which jumps to __kuser_get_tls.
    35	// The replacement function saves LR in R11 over the call to read_tls_fallback.
    36	// To make stack unwinding work, this function should NOT be marked as NOFRAME,
    37	// as it may contain a call, which clobbers LR even just temporarily.
    38	MRC	15, 0, R0, C13, C0, 3 // fetch TLS base pointer
    39	BIC $3, R0 // Darwin/ARM might return unaligned pointer
    40	MOVW	runtime·tls_g(SB), R11
    41	ADD	R11, R0
    42	MOVW	g, 0(R0)
    43	MOVW	g, R0 // preserve R0 across call to setg<>
    44	RET
    45
    46// load_g loads the g register from pthread-provided
    47// thread-local memory, for use after calling externally compiled
    48// ARM code that overwrote those registers.
    49TEXT runtime·load_g(SB),NOSPLIT,$0
    50	// See save_g
    51	MRC	15, 0, R0, C13, C0, 3 // fetch TLS base pointer
    52	BIC $3, R0 // Darwin/ARM might return unaligned pointer
    53	MOVW	runtime·tls_g(SB), R11
    54	ADD	R11, R0
    55	MOVW	0(R0), g
    56	RET
    57
    58// This is called from rt0_go, which runs on the system stack
    59// using the initial stack allocated by the OS.
    60// It calls back into standard C using the BL (R4) below.
    61// To do that, the stack pointer must be 8-byte-aligned
    62// on some systems, notably FreeBSD.
    63// The ARM ABI says the stack pointer must be 8-byte-aligned
    64// on entry to any function, but only FreeBSD's C library seems to care.
    65// The caller was 8-byte aligned, but we push an LR.
    66// Declare a dummy word ($4, not $0) to make sure the
    67// frame is 8 bytes and stays 8-byte-aligned.
    68TEXT runtime·_initcgo(SB),NOSPLIT,$4
    69	// if there is an _cgo_init, call it.
    70	MOVW	_cgo_init(SB), R4
    71	CMP	$0, R4
    72	B.EQ	nocgo
    73	MRC     15, 0, R0, C13, C0, 3 	// load TLS base pointer
    74	MOVW 	R0, R3 			// arg 3: TLS base pointer
    75#ifdef TLSG_IS_VARIABLE
    76	MOVW 	$runtime·tls_g(SB), R2 	// arg 2: &tls_g
    77#else
    78	MOVW	$0, R2			// arg 2: not used when using platform tls
    79#endif
    80	MOVW	$setg_gcc<>(SB), R1 	// arg 1: setg
    81	MOVW	g, R0 			// arg 0: G
    82	BL	(R4) // will clobber R0-R3
    83nocgo:
    84	RET
    85
    86// void setg_gcc(G*); set g called from gcc.
    87TEXT setg_gcc<>(SB),NOSPLIT,$0
    88	MOVW	R0, g
    89	B		runtime·save_g(SB)
    90
    91#ifdef TLSG_IS_VARIABLE
    92#ifdef GOOS_android
    93// Use the free TLS_SLOT_APP slot #2 on Android Q.
    94// Earlier androids are set up in gcc_android.c.
    95DATA runtime·tls_g+0(SB)/4, $8
    96#endif
    97GLOBL runtime·tls_g+0(SB), NOPTR, $4
    98#else
    99GLOBL runtime·tls_g+0(SB), TLSBSS, $4
   100#endif
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