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Russ Cox 54c901cd08 runtime: fix empty string handling in garbage collector 
The garbage collector uses type information to guide the
traversal of the heap. If it sees a field that should be a string,
it marks the object pointed at by the string data pointer as
visited but does not bother to look at the data, because
strings contain bytes, not pointers.

If you save s[len(s):] somewhere, though, the string data pointer
actually points just beyond the string data; if the string data
were exactly the size of an allocated block, the string data
pointer would actually point at the next block. It is incorrect
to mark that next block as visited and not bother to look at
the data, because the next block may be some other type
entirely.

The fix is to ignore strings with zero length during collection:
they are empty and can never become non-empty: the base
pointer will never be used again. The handling of slices already
does this (but using cap instead of len).

This was not a bug in Go 1.2, because until January all string
allocations included a trailing NUL byte not included in the
length, so s[len(s):] still pointed inside the string allocation
(at the NUL).

This bug was causing the crashes in test/run.go. Specifically,
the parsing of a regexp in package regexp/syntax allocated a
[]syntax.Inst with rounded size 1152 bytes. In fact it
allocated many such slices, because during the processing of
test/index2.go it creates thousands of regexps that are all
approximately the same complexity. That takes a long time, and
test/run works on other tests in other goroutines. One such
other test is chan/perm.go, which uses an 1152-byte source
file. test/run reads that file into a []byte and then calls
strings.Split(string(src), "\n"). The string(src) creates an
1152-byte string - and there's a very good chance of it
landing next to one of the many many regexp slices already
allocated - and then because the file ends in a \n,
strings.Split records the tail empty string as the final
element in the slice. A garbage collection happens at this
point, the collection finds that string before encountering
the []syntax.Inst data it now inadvertently points to, and the
[]syntax.Inst data is not scanned for the pointers that it
contains. Each syntax.Inst contains a []rune, those are
missed, and the backing rune arrays are freed for reuse. When
the regexp is later executed, the runes being searched for are
no longer runes at all, and there is no match, even on text
that should match.

On 64-bit machines the pointer in the []rune inside the
syntax.Inst is larger (along with a few other pointers),
pushing the []syntax.Inst backing array into a larger size
class, avoiding the collision with chan/perm.go's
inadvertently sized file.

I expect this was more prevalent on OS X than on Linux or
Windows because those managed to run faster or slower and
didn't overlap index2.go with chan/perm.go as often. On the
ARM systems, we only run one errorcheck test at a time, so
index2 and chan/perm would never overlap.

It is possible that this bug is the root cause of other crashes
as well. For now we only know it is the cause of the test/run crash.

Many thanks to Dmitriy for help debugging.

Fixes #7344.
Fixes #7455.

LGTM=r, dvyukov, dave, iant
R=golang-codereviews, dave, r, dvyukov, delpontej, iant
CC=golang-codereviews, khr
https://golang.org/cl/74250043
2014-03-11 23:58:39 -04:00
..
bench test: revert unintentional commits 2013-11-19 15:36:13 +04:00
bugs cmd/gc: fix wrong interaction between inlining and embedded builtins. 2012-12-22 19:16:31 +01:00
chan test/chan: avoid wrap-around in memstats comparison 2013-09-20 17:27:56 -07:00
ddd2.dir test: convert tests to run.go whenever possible. 2012-10-10 22:35:27 +02:00
dwarf test: make rundir match compiledir/errorcheckdir. 2013-01-11 22:00:48 +01:00
fixedbugs liblink: fix bad code generated for MOVFD/MOVDF when reg > 7 2014-03-11 14:04:44 -04:00
import2.dir test: convert more tests to rundir/compiledir conventions 2012-10-07 23:22:01 +02:00
import4.dir test: match gccgo import error messages 2013-12-12 19:02:11 -08:00
interface cmd/gc: don't attempt to generate wrappers for blank interface methods 2013-08-19 11:53:34 +10:00
ken go/test/chan1.go: fix typo 2012-02-25 08:47:04 +11:00
method4.dir cmd/gc: do not omit wrapper for expression (interface{...}).F 2014-01-07 13:26:48 +01:00
safe test: adapt old-style tests to new flag parsing. 2013-01-11 22:05:46 +01:00
stress test/stress: fix a goroutine leak in threadRing stresstest 2013-06-03 07:07:31 -07:00
syntax test: match gccgo error messages 2013-12-12 17:18:12 -08:00
64bit.go cmd/gc: Error out on division by constant zero. 2013-01-30 20:21:08 +01:00
235.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
alias.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
alias1.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
append.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
args.go test: run some more tests by default 2012-11-08 09:04:27 -08:00
assign.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
assign1.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
bigalg.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
bigmap.go runtime: handle and test large map values 2012-05-24 22:41:07 -04:00
blank.go test: revert changes made for Go SSA interpreter test. 2013-10-08 14:36:20 -04:00
blank1.go test: match gccgo error messages for blank1.go 2013-09-28 15:19:05 -07:00
bom.go gc: initial BOM is legal. 2012-09-10 13:03:07 -07:00
bombad.go gc: initial BOM is legal. 2012-09-10 13:03:07 -07:00
bounds.go test: prepare for 64-bit ints 2012-09-24 00:06:41 -04:00
chancap.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
char_lit.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
char_lit1.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
closedchan.go test: use testlib (first 100) 2012-02-16 23:48:57 -05:00
closure.go test: enforce 1 proc in the test 2012-07-01 21:59:50 +04:00
cmp.go cmd/gc: do not nop-convert equivalent but different interface types. 2014-02-27 08:07:50 +01:00
cmp6.go cmd/gc: do not consider length zero arrays as comparable. 2014-01-31 00:30:56 +01:00
cmplx.go cmd/gc: reject complex calls with mismatched argument types. 2013-03-11 22:55:14 +01:00
cmplxdivide.c test: use testlib in a few more cases 2012-03-22 02:14:44 +08:00
cmplxdivide.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
cmplxdivide1.go test: use testlib in a few more cases 2012-03-22 02:14:44 +08:00
complit.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
complit1.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
compos.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
const.go exp/ssa/interp: (#6 of 5): test interpretation of SSA form of $GOROOT/test/*.go. 2013-02-21 12:48:38 -05:00
const1.go test: match gccgo error messages 2013-12-12 17:18:12 -08:00
const2.go test: match gccgo error messages 2012-09-28 08:30:30 -07:00
const3.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
const4.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
const5.go cmd/gc: reject non-Go constants 2013-02-01 23:10:02 -05:00
const6.go test: match gccgo error strings. 2013-06-26 18:05:02 +02:00
convert.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
convert1.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
convert3.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
convlit.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
convlit1.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
convT2X.go cmd/gc: cache itab lookup in convT2I. 2012-07-03 09:09:05 +10:00
copy.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
crlf.go test: use testlib in a few more cases (part 2) 2012-04-20 23:45:43 +08:00
ddd.go test: enable method expression tests in ddd.go 2012-03-07 11:17:26 -08:00
ddd1.go test: match gccgo error messages 2012-09-28 08:30:30 -07:00
ddd2.go test: convert tests to run.go whenever possible. 2012-10-10 22:35:27 +02:00
decl.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
declbad.go test: correct type in declbad.go 2012-10-07 21:52:57 +02:00
defer.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
deferfin.go runtime: combine small NoScan allocations 2014-01-24 22:35:11 +04:00
deferprint.go test: add cmpout to testlib 2012-02-24 13:17:26 +11:00
deferprint.out test: split golden.out into expected output per test 2012-01-18 16:12:24 -08:00
divide.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
divmod.go all: fix a few spelling errors in source comments 2013-12-27 08:59:02 -08:00
empty.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
env.go os: remove Getenverror 2012-02-18 21:18:13 -08:00
eof.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
eof1.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
errchk test/errchk: use "#!/usr/bin/env perl" shebang line 2013-05-23 04:41:22 +08:00
escape.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
escape2.go cmd/gc: relax address-of escape analysis 2014-02-13 19:59:09 -05:00
escape3.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
escape4.go cmd/gc: fix escape analysis bug 2012-09-24 15:53:12 -04:00
escape5.go cmd/gc: distinguish unnamed vs blank-named return variables better 2014-02-13 20:59:39 -05:00
float_lit.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
floatcmp.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
for.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
func.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
func1.go cmd/gc: ensure unique parameter and result names in function types 2013-03-15 15:24:13 -04:00
func2.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
func3.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
func4.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
func5.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
func6.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
func7.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
func8.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
funcdup.go test: match gccgo error messages 2013-12-12 17:18:12 -08:00
funcdup2.go test: match gccgo error messages 2013-12-12 17:18:12 -08:00
gc.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
gc1.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
gc2.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
gcstring.go runtime: fix empty string handling in garbage collector 2014-03-11 23:58:39 -04:00
golden.out cmd/gc: do not generate code for var _ = ... unless necessary 2012-12-30 12:01:53 -05:00
goprint.go test: make goprint.go wait longer for go its routine to execute 2013-04-12 16:04:19 -07:00
goprint.out test: split golden.out into expected output per test 2012-01-18 16:12:24 -08:00
goto.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
helloworld.go test: add cmpout to testlib 2012-02-24 13:17:26 +11:00
helloworld.out test: split golden.out into expected output per test 2012-01-18 16:12:24 -08:00
if.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
import.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
import1.go test: match gccgo import error messages 2013-12-12 19:02:11 -08:00
import2.go test: convert more tests to rundir/compiledir conventions 2012-10-07 23:22:01 +02:00
import4.go test: convert more tests to rundir/compiledir conventions 2012-10-07 23:22:01 +02:00
import5.go gc: disallow absolute import paths 2012-02-29 15:28:36 -05:00
index.go test: recognize gccgo error message in index.go 2013-09-27 20:38:52 -07:00
index0.go test: run index test by default 2012-11-07 12:33:54 -08:00
index1.go test: run index test by default 2012-11-07 12:33:54 -08:00
index2.go test: run index test by default 2012-11-07 12:33:54 -08:00
indirect.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
indirect1.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
init.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
init1.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
initcomma.go test/initcomma.go: restore what it's supposed to be testing 2012-02-20 07:44:24 +11:00
initialize.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
initializerr.go test: add "duplicate" struct map key test 2012-12-17 11:05:58 -05:00
int_lit.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
intcvt.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
iota.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
label.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
label1.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
linkx.go test: expand run.go's errorcheck, make clear which bugs run 2012-09-23 13:16:14 -04:00
literal.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
live.go cmd/gc: correct liveness for fat variables 2014-02-15 10:58:55 -05:00
live1.go cmd/gc: correct liveness for fat variables 2014-02-15 10:58:55 -05:00
mallocfin.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
map.go test: fix flaky NaN-key map complexity test 2013-04-07 11:56:15 -07:00
map1.go cmd/gc: fix type checking loop 2012-06-07 03:06:40 -04:00
mapnan.go test/mapnan: use time.Now instead of syscall.Getrusage 2013-10-22 18:33:37 -04:00
method.go test: a number of fixes. 2013-02-11 18:20:52 -05:00
method1.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
method2.go cmd/gc: fix method values whose receiver is an unnamed interface. 2013-08-29 10:00:58 +02:00
method3.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
method4.go test: convert more tests to rundir/compiledir conventions 2012-10-07 23:22:01 +02:00
method5.go cmd/gc: implement method values 2013-03-20 17:11:09 -04:00
named.go gc: return of ideal bool 2012-02-21 22:54:07 -05:00
named1.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
nil.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
nilcheck.go cmd/gc: &x panics if x does 2013-08-15 14:38:32 -04:00
nilptr.go test/nilptr: add more tests 2013-09-05 23:06:34 -04:00
nilptr2.go test: revert changes made for Go SSA interpreter test. 2013-10-08 14:36:20 -04:00
nilptr3.go cmd/gc: eliminate redundant &x.Field nil checks 2013-09-17 16:54:22 -04:00
nilptr4.go cmd/gc: fix bad checknil with ints on 32 bit compilers 2014-02-26 12:25:13 -08:00
nul1.go test: run some more tests by default 2012-11-08 09:04:27 -08:00
parentype.go test/[n-r]*.go: add documentation 2012-02-24 10:30:39 +11:00
peano.go test/[n-r]*.go: add documentation 2012-02-24 10:30:39 +11:00
printbig.go test: add cmpout to testlib 2012-02-24 13:17:26 +11:00
printbig.out test: split golden.out into expected output per test 2012-01-18 16:12:24 -08:00
range.go test: a number of fixes. 2013-02-11 18:20:52 -05:00
recover.go test: disable failing tests under ssa/interp. 2013-09-18 14:44:57 -04:00
recover1.go test: use testlib (final 61) 2012-02-16 23:51:04 -05:00
recover2.go test: use testlib (final 61) 2012-02-16 23:51:04 -05:00
recover3.go tests: remove two misuses of nil pointers 2013-08-15 11:51:04 -04:00
rename.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
rename1.go test: fix the fix of the rename tests. 2012-02-24 15:06:32 +11:00
reorder.go test: a number of fixes. 2013-02-11 18:20:52 -05:00
reorder2.go test/[n-r]*.go: add documentation 2012-02-24 10:30:39 +11:00
return.go test: add cases to return.go that gccgo got wrong 2013-08-07 11:31:01 -07:00
rotate.go test: add rotate.go and fixedbugs/bug313 2013-01-11 22:42:55 +01:00
rotate0.go test: add rotate.go and fixedbugs/bug313 2013-01-11 22:42:55 +01:00
rotate1.go test: add rotate.go and fixedbugs/bug313 2013-01-11 22:42:55 +01:00
rotate2.go test: add rotate.go and fixedbugs/bug313 2013-01-11 22:42:55 +01:00
rotate3.go test: add rotate.go and fixedbugs/bug313 2013-01-11 22:42:55 +01:00
run test/run: add /usr/pkg/bin to PATH. 2014-03-03 02:16:15 -05:00
run.go test/run: make errorcheck tests faster 2014-03-11 23:58:24 -04:00
rune.go test/[n-r]*.go: add documentation 2012-02-24 10:30:39 +11:00
runtime.go test/[n-r]*.go: add documentation 2012-02-24 10:30:39 +11:00
shift1.go test/shift1.go: recognize gccgo errors 2013-06-26 08:23:52 -07:00
shift2.go test: add shift expression incorrectly rejected by gccgo. 2013-06-25 08:06:34 +02:00
sieve.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
sigchld.go test: skip SIGCHLD test on Plan 9 2014-01-29 09:28:23 +01:00
sigchld.out test: split golden.out into expected output per test 2012-01-18 16:12:24 -08:00
simassign.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
sinit.go cmd/gc: do not generate code for var _ = ... unless necessary 2012-12-30 12:01:53 -05:00
sizeof.go test: correct sizeof.go. 2013-06-02 19:10:11 +02:00
slice3.go cmd/gc: support x[i:j:k] 2013-07-01 20:32:36 -04:00
slice3err.go test: match gccgo error messages 2013-12-12 17:18:12 -08:00
solitaire.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
stack.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
string_lit.go test: add []rune case to string_lit.go 2013-12-12 17:17:02 -08:00
stringrange.go all: make Unicode surrogate halves illegal as UTF-8 2012-08-08 14:01:23 -07:00
struct0.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
switch.go cmd/gc: disallow fallthrough in final case of switch 2013-03-15 00:35:09 -04:00
switch3.go cmd/gc: accept switches on comparable arrays. 2012-08-03 21:47:26 +02:00
switch4.go cmd/gc: disallow fallthrough in final case of switch 2013-03-15 00:35:09 -04:00
testlib test/run: process build tags like go/build 2013-08-13 12:25:41 -04:00
tinyfin.go runtime: combine small NoScan allocations 2014-01-24 22:35:11 +04:00
torture.go cmd/8g: introduce temporaries in byte multiplication. 2012-12-21 23:46:16 +01:00
turing.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
typecheck.go cmd/gc: silence assignment errors to undefined symbols 2014-01-03 21:03:20 +01:00
typeswitch.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
typeswitch1.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
typeswitch2.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
typeswitch3.go test: match gccgo error messages 2012-09-28 08:30:30 -07:00
undef.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
utf.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
varerr.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
varinit.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
zerodivide.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00