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cmd/internal/obj/x86: allow non-zero offset in TLS reference

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An instruction that references TLS, e.g.

MOVQ	0(TLS), AX

on some platforms (e.g. Android), or in shared mode, may be
translated to (assuming TLS offset already loaded to CX)

MOVQ	0(CX)(TLS*1), AX

which in turns translates to

movq	%fs:(%rcx), %rax

We have rejected non-zero offset for TLS reference, like 16(TLS).
Actually, the instruction can take offset, i.e. it is a valid
instruction for, e.g.,

movq	%fs:16(%rcx),%rcx

So, allow offset in TLS reference.

Change-Id: Iaf1996bad7fe874e0c298ea441af5acb136a4028
Reviewed-on: https://go-review.googlesource.com/c/go/+/171151
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Cherry Zhang 2019-04-09 12:10:27 -04:00
parent 016625c265
commit 68c664141c
3 changed files with 13 additions and 11 deletions
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4
src/cmd/asm/internal/asm/testdata/386.s vendored
View File

@ -89,6 +89,10 @@ label:
loop:
LOOP loop // LOOP
// Tests for TLS reference.
MOVL (TLS), AX
MOVL 8(TLS), DX
// LTYPE0 nonnon { outcode(int($1), &$2); }
RET
RET foo(SB)

4
src/cmd/asm/internal/asm/testdata/amd64.s vendored
View File

@ -143,6 +143,10 @@ loop:
MOVB foo+32(SP)(CX*4), AH // 8a648c20
MOVB foo+32323(SP)(CX*8), R9 // 448a8ccc437e0000
// Tests for TLS reference.
MOVQ (TLS), AX
MOVQ 8(TLS), DX
// LTYPE0 nonnon { outcode($1, &$2); }
RET // c3
RET foo(SB)

16
src/cmd/internal/obj/x86/asm6.go
View File

@ -2345,17 +2345,14 @@ func prefixof(ctxt *obj.Link, a *obj.Addr) int {
if ctxt.Arch.Family == sys.I386 {
if a.Index == REG_TLS && ctxt.Flag_shared {
// When building for inclusion into a shared library, an instruction of the form
// MOVL 0(CX)(TLS*1), AX
// MOVL off(CX)(TLS*1), AX
// becomes
// mov %gs:(%ecx), %eax
// mov %gs:off(%ecx), %eax
// which assumes that the correct TLS offset has been loaded into %ecx (today
// there is only one TLS variable -- g -- so this is OK). When not building for
// a shared library the instruction it becomes
// mov 0x0(%ecx), $eax
// mov 0x0(%ecx), %eax
// and a R_TLS_LE relocation, and so does not require a prefix.
if a.Offset != 0 {
ctxt.Diag("cannot handle non-0 offsets to TLS")
}
return 0x65 // GS
}
return 0
@ -2374,15 +2371,12 @@ func prefixof(ctxt *obj.Link, a *obj.Addr) int {
case REG_TLS:
if ctxt.Flag_shared && ctxt.Headtype != objabi.Hwindows {
// When building for inclusion into a shared library, an instruction of the form
// MOV 0(CX)(TLS*1), AX
// MOV off(CX)(TLS*1), AX
// becomes
// mov %fs:(%rcx), %rax
// mov %fs:off(%rcx), %rax
// which assumes that the correct TLS offset has been loaded into %rcx (today
// there is only one TLS variable -- g -- so this is OK). When not building for
// a shared library the instruction does not require a prefix.
if a.Offset != 0 {
log.Fatalf("cannot handle non-0 offsets to TLS")
}
return 0x64
}