code review 106380043: cmd/go, cmd/ld, runtime, os/user: TLS emultion for android

src/pkg/runtime/asm_arm.s

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 #include "zasm_GOOS_GOARCH.h"
 #include "funcdata.h"
 #include "../../cmd/ld/textflag.h"
 
 // using frame size $-4 means do not save LR on stack.
 TEXT _rt0_go(SB),NOSPLIT,$-4
@@ skipping 22 matching lines @@
         MOVW    $(-8192+104)(R13), R0
         MOVW    R0, g_stackguard(g)     // (w 104b guard)
         MOVW    R0, g_stackguard0(g)
         MOVW    R13, g_stackbase(g)
         BL      runtime·emptyfunc(SB)   // fault if stack check is wrong
 
         // if there is an _cgo_init, call it.
         MOVW    _cgo_init(SB), R4
         CMP     $0, R4
         B.EQ    nocgo
-        BL              runtime·save_g(SB);
-        MOVW    g, R0 // first argument of _cgo_init is g
-        MOVW    $setg_gcc<>(SB), R1 // second argument is address of save_g
-        BL              (R4) // will clobber R0-R3
+        MOVW    g, R0                   // arg 0: G

[dave_cheney.net, 2014/07/02 04:33:05]

if you're going to inline setg_gcc, please retain the comment.

[crawshaw, 2014/07/02 14:57:22]

sorry, which comment?

+        MOVW    $setg_gcc<>(SB), R1     // arg 1: setg
+        MOVW.NE $runtime·tlsg(SB), R2   // arg 2: tlsg

[minux, 2014/07/02 04:21:14]

.NE is unnecessary here.

[crawshaw, 2014/07/02 14:57:22]

Done.

+        MRC     15, 0, R3, C13, C0, 3   // arg 3: TLS base pointer

[minux, 2014/07/02 04:21:14]

because this instruction will be rewritten by the liblink if
GOARM < 7 to a BL runtime.read_tls_fallback(SB) instruction,
you have to use R0 for the register here.

otherwise you will break build for linux/arm with GOARM < 7.

also note, if you change the argument order, please also keep
the x_cgo_init function in pkg/runtime/cgo/gcc_{free,net}bsd_arm.c
up-to-date.

I will add a explicit check to liblink/obj5.c to diagnose
this case. (CL 107430044)

[crawshaw, 2014/07/02 14:57:22]

thank you, I have been testing exclusively with GOARM=7. I wish there were some
way I could run a CL through all the builders.

bouncing this instruction through R0.

+        BL      (R4) // will clobber R0-R3
 
 nocgo:
         // update stackguard after _cgo_init
         MOVW    g_stackguard0(g), R0
         MOVW    R0, g_stackguard(g)
 
         BL      runtime·checkgoarm(SB)
         BL      runtime·check(SB)
 
         // saved argc, argv
@@ skipping 624 matching lines @@
 _eqnext:
         CMP     R2, R6
         RET.EQ
         MOVBU.P 1(R2), R4
         MOVBU.P 1(R3), R5
         CMP     R4, R5
         BEQ     _eqnext
         MOVB    R7, v+16(FP)
         RET
 
-// We have to resort to TLS variable to save g(R10).
-// One reason is that external code might trigger
-// SIGSEGV, and our runtime.sigtramp don't even know we
-// are in external code, and will continue to use R10,
-// this might as well result in another SIGSEGV.
-// Note: all three functions will clobber R0, and the last
-// two can be called from 5c ABI code.
-
-// save_g saves the g register into pthread-provided
-// thread-local memory, so that we can call externally compiled
-// ARM code that will overwrite those registers.
-// NOTE: runtime.gogo assumes that R1 is preserved by this function.
-//       runtime.mcall assumes this function only clobbers R0 and R11.
-TEXT runtime·save_g(SB),NOSPLIT,$0
-        MRC             15, 0, R0, C13, C0, 3 // fetch TLS base pointer
-        // $runtime.tlsg(SB) is a special linker symbol.
-        // It is the offset from the TLS base pointer to our
-        // thread-local storage for g.
-        MOVW    $runtime·tlsg(SB), R11
-        ADD     R11, R0
-        MOVW    g, 0(R0)
-        RET
-
-// load_g loads the g register from pthread-provided
-// thread-local memory, for use after calling externally compiled
-// ARM code that overwrote those registers.
-TEXT runtime·load_g(SB),NOSPLIT,$0
-        MRC             15, 0, R0, C13, C0, 3 // fetch TLS base pointer
-        // $runtime.tlsg(SB) is a special linker symbol.
-        // It is the offset from the TLS base pointer to our
-        // thread-local storage for g.
-        MOVW    $runtime·tlsg(SB), R11
-        ADD     R11, R0
-        MOVW    0(R0), g
-        RET
-
 // void setg_gcc(G*); set g called from gcc.
 TEXT setg_gcc<>(SB),NOSPLIT,$0
         MOVW    R0, g
         B               runtime·save_g(SB)
 
 // TODO: share code with memeq?
 TEXT bytes·Equal(SB),NOSPLIT,$0
         MOVW    a_len+4(FP), R1
         MOVW    b_len+16(FP), R3
 ········
@@ skipping 473 matching lines @@
         MOVW.P  R0, 4(R2)
         MOVW.P  4(R1), R0
         MOVW.P  R0, 4(R2)
         MOVW.P  4(R1), R0
         MOVW.P  R0, 4(R2)
         MOVW.P  4(R1), R0
         MOVW.P  R0, 4(R2)
         MOVW.P  4(R1), R0
         MOVW.P  R0, 4(R2)
         RET