github.com/comwrg/go/src@v0.0.0-20220319063731-c238d0440370/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 //go:build !windows 6 // +build !windows 7 8 #include "go_asm.h" 9 #include "go_tls.h" 10 #include "funcdata.h" 11 #include "textflag.h" 12 13 // We have to resort to TLS variable to save g(R10). 14 // One reason is that external code might trigger 15 // SIGSEGV, and our runtime.sigtramp don't even know we 16 // are in external code, and will continue to use R10, 17 // this might as well result in another SIGSEGV. 18 // Note: both functions will clobber R0 and R11 and 19 // can be called from 5c ABI code. 20 21 // On android, runtime.tls_g is a normal variable. 22 // TLS offset is computed in x_cgo_inittls. 23 #ifdef GOOS_android 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|NOFRAME,$0 34 // If the host does not support MRC the linker will replace it with 35 // a call to runtime.read_tls_fallback which jumps to __kuser_get_tls. 36 // The replacement function saves LR in R11 over the call to read_tls_fallback. 37 MRC 15, 0, R0, C13, C0, 3 // fetch TLS base pointer 38 BIC $3, R0 // Darwin/ARM might return unaligned pointer 39 MOVW runtime·tls_g(SB), R11 40 ADD R11, R0 41 MOVW g, 0(R0) 42 MOVW g, R0 // preserve R0 across call to setg<> 43 RET 44 45 // load_g loads the g register from pthread-provided 46 // thread-local memory, for use after calling externally compiled 47 // ARM code that overwrote those registers. 48 TEXT runtime·load_g(SB),NOSPLIT,$0 49 // See save_g 50 MRC 15, 0, R0, C13, C0, 3 // fetch TLS base pointer 51 BIC $3, R0 // Darwin/ARM might return unaligned pointer 52 MOVW runtime·tls_g(SB), R11 53 ADD R11, R0 54 MOVW 0(R0), g 55 RET 56 57 // This is called from rt0_go, which runs on the system stack 58 // using the initial stack allocated by the OS. 59 // It calls back into standard C using the BL (R4) below. 60 // To do that, the stack pointer must be 8-byte-aligned 61 // on some systems, notably FreeBSD. 62 // The ARM ABI says the stack pointer must be 8-byte-aligned 63 // on entry to any function, but only FreeBSD's C library seems to care. 64 // The caller was 8-byte aligned, but we push an LR. 65 // Declare a dummy word ($4, not $0) to make sure the 66 // frame is 8 bytes and stays 8-byte-aligned. 67 TEXT runtime·_initcgo(SB),NOSPLIT,$4 68 // if there is an _cgo_init, call it. 69 MOVW _cgo_init(SB), R4 70 CMP $0, R4 71 B.EQ nocgo 72 MRC 15, 0, R0, C13, C0, 3 // load TLS base pointer 73 MOVW R0, R3 // arg 3: TLS base pointer 74 #ifdef TLSG_IS_VARIABLE 75 MOVW $runtime·tls_g(SB), R2 // arg 2: &tls_g 76 #else 77 MOVW $0, R2 // arg 2: not used when using platform tls 78 #endif 79 MOVW $setg_gcc<>(SB), R1 // arg 1: setg 80 MOVW g, R0 // arg 0: G 81 BL (R4) // will clobber R0-R3 82 nocgo: 83 RET 84 85 // void setg_gcc(G*); set g called from gcc. 86 TEXT setg_gcc<>(SB),NOSPLIT,$0 87 MOVW R0, g 88 B runtime·save_g(SB) 89 90 #ifdef TLSG_IS_VARIABLE 91 #ifdef GOOS_android 92 // Use the free TLS_SLOT_APP slot #2 on Android Q. 93 // Earlier androids are set up in gcc_android.c. 94 DATA runtime·tls_g+0(SB)/4, $8 95 #endif 96 GLOBL runtime·tls_g+0(SB), NOPTR, $4 97 #else 98 GLOBL runtime·tls_g+0(SB), TLSBSS, $4 99 #endif