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cmd/internal/obj, runtime: fixes for defer in 386 shared libraries

Any defer in a shared object crashed when GOARCH=386. This turns out to be two
bugs:

 1) Calls to morestack were not processed to be PIC safe (must have been
    possible to trigger this another way too)
 2) jmpdefer needs to rewind the return address of the deferred function past
    the instructions that load the GOT pointer into BX, not just past the call

Bug 2) requires re-introducing the a way for .s files to know when they are
being compiled for dynamic linking but I've tried to do that in as minimal
a way as possible.

Fixes #15916

Change-Id: Ia0d09b69ec272a176934176b8eaef5f3bfcacf04
Reviewed-on: https://go-review.googlesource.com/23623
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Michael Hudson-Doyle 2016-06-02 11:07:55 +12:00
parent 5799973c3e
commit 26849746c9
4 changed files with 29 additions and 3 deletions

View File

@ -17,5 +17,6 @@ func (d *Dep) Method() int {
}
func F() int {
defer func() {}()
return V
}

View File

@ -2328,7 +2328,15 @@ func (gcToolchain) asm(b *builder, p *Package, obj, ofile, sfile string) error {
// Add -I pkg/GOOS_GOARCH so #include "textflag.h" works in .s files.
inc := filepath.Join(goroot, "pkg", "include")
sfile = mkAbs(p.Dir, sfile)
args := []interface{}{buildToolExec, tool("asm"), "-o", ofile, "-trimpath", b.work, "-I", obj, "-I", inc, "-D", "GOOS_" + goos, "-D", "GOARCH_" + goarch, buildAsmflags, sfile}
args := []interface{}{buildToolExec, tool("asm"), "-o", ofile, "-trimpath", b.work, "-I", obj, "-I", inc, "-D", "GOOS_" + goos, "-D", "GOARCH_" + goarch, buildAsmflags}
if p.ImportPath == "runtime" && goarch == "386" {
for _, arg := range buildAsmflags {
if arg == "-dynlink" {
args = append(args, "-D=GOBUILDMODE_shared=1")
}
}
}
args = append(args, sfile)
if err := b.run(p.Dir, p.ImportPath, nil, args...); err != nil {
return err
}

View File

@ -1092,6 +1092,7 @@ func stacksplit(ctxt *obj.Link, p *obj.Prog, framesize int32, textarg int32) *ob
call.Mode = ctxt.Cursym.Text.Mode
call.As = obj.ACALL
call.To.Type = obj.TYPE_BRANCH
call.To.Name = obj.NAME_EXTERN
morestack := "runtime.morestack"
switch {
case ctxt.Cursym.Cfunc:
@ -1100,8 +1101,17 @@ func stacksplit(ctxt *obj.Link, p *obj.Prog, framesize int32, textarg int32) *ob
morestack = "runtime.morestack_noctxt"
}
call.To.Sym = obj.Linklookup(ctxt, morestack, 0)
// When compiling 386 code for dynamic linking, the call needs to be adjusted
// to follow PIC rules. This in turn can insert more instructions, so we need
// to keep track of the start of the call (where the jump will be to) and the
// end (which following instructions are appended to).
callend := call
progedit(ctxt, callend)
for ; callend.Link != nil; callend = callend.Link {
progedit(ctxt, callend.Link)
}
jmp := obj.Appendp(ctxt, call)
jmp := obj.Appendp(ctxt, callend)
jmp.As = obj.AJMP
jmp.To.Type = obj.TYPE_BRANCH
jmp.Pcond = ctxt.Cursym.Text.Link

View File

@ -539,13 +539,20 @@ TEXT ·publicationBarrier(SB),NOSPLIT,$0-0
// void jmpdefer(fn, sp);
// called from deferreturn.
// 1. pop the caller
// 2. sub 5 bytes from the callers return
// 2. sub 5 bytes (the length of CALL & a 32 bit displacement) from the callers
// return (when building for shared libraries, subtract 16 bytes -- 5 bytes
// for CALL & displacement to call __x86.get_pc_thunk.cx, 6 bytes for the
// LEAL to load the offset into BX, and finally 5 for the call & displacement)
// 3. jmp to the argument
TEXT runtime·jmpdefer(SB), NOSPLIT, $0-8
MOVL fv+0(FP), DX // fn
MOVL argp+4(FP), BX // caller sp
LEAL -4(BX), SP // caller sp after CALL
#ifdef GOBUILDMODE_shared
SUBL $16, (SP) // return to CALL again
#else
SUBL $5, (SP) // return to CALL again
#endif
MOVL 0(DX), BX
JMP BX // but first run the deferred function