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
Some of the errorcheck tests have many many identical regexps.
Use a map to avoid storing the compiled form many many times
in memory. Change the filterRe to a simple string to avoid
the expense of those regexps as well.
Cuts the time for run.go on index2.go by almost 50x.
Noticed during debugging of issue 7344.
LGTM=bradfitz
R=bradfitz, josharian
CC=golang-codereviews
https://golang.org/cl/74380043
debuglive >= 1 is not the condition under which we
start recording messages (we avoid printing for
init functions even if debuglive is set).
LGTM=bradfitz, iant
R=golang-codereviews, bradfitz
CC=golang-codereviews, iant, khr
https://golang.org/cl/74390043
For now Note, futexsleep and futexwakeup are designed for threads,
not for processes. The explicit use of UMTX_OP_WAIT_UINT_PRIVATE and
UMTX_OP_WAKE_PRIVATE can avoid unnecessary traversals of VM objects,
to hit undiscovered bugs related to VM system on SMP/SMT/NUMA
environment.
Update #7496
LGTM=iant
R=golang-codereviews, gobot, iant, bradfitz
CC=golang-codereviews
https://golang.org/cl/72760043
Solaris doesn't have struct ip_mreqn, instead it uses struct ip_mreq
and struct group_req with struct sockaddr_storage.
Also fixes incorrect SockaddrDatalink.
Update #7399
LGTM=aram, iant
R=golang-codereviews, aram, gobot, iant
CC=golang-codereviews
https://golang.org/cl/73920043
This CL is a reformulation of CL 73110043 containing only the minimum required to get the nacl builds compiling.
LGTM=bradfitz
R=rsc, bradfitz
CC=golang-codereviews
https://golang.org/cl/74220043
The comment for 'Clean' function is prepended with spaces instead of
a single tab, resulting in visually misaligned comment in the generated
documentation.
LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/73840043
The change to signal_amd64.c from CL 15790043 was not merged correctly.
This CL reapplies the change, renaming the file to signal_amd64x.c and adds the appropriate build tags.
LGTM=iant, bradfitz
R=rsc, iant, bradfitz
CC=golang-codereviews
https://golang.org/cl/72790043
The byte that r is or'd into is already 0x7, so the failure to zero r only
impacts the generated machine code if the register is > 7.
Fixes#7044.
LGTM=dave, minux.ma, rsc
R=dave, minux.ma, bradfitz, rsc
CC=golang-codereviews
https://golang.org/cl/73730043
Spans are now private to threads, and the loop
is removed from all other functions.
Remove it from marknogc for consistency.
LGTM=khr, rsc
R=golang-codereviews, bradfitz, khr
CC=golang-codereviews, khr, rsc
https://golang.org/cl/72520043
Not many windows users have perl installed. They can just use
standard go tools instead. Also mkerrors_windows.sh script
removed - we don't add any new "unix" errors to windows
syscall package anymore.
LGTM=rsc
R=golang-codereviews, rsc
CC=golang-codereviews
https://golang.org/cl/41060044
Thanks to Ian for spotting these.
runtime.h: define uintreg correctly.
stack.c: address warning caused by the type of uintreg being 32 bits on amd64p32.
Commentary (mainly for my own use)
nacl/amd64p32 defines a machine with 64bit registers, but address space is limited to a 4gb window (the window is placed randomly inside the full 48 bit virtual address space of a process). To cope with this 6c defines _64BIT and _64BITREG.
_64BITREG is always defined by 6c, so both GOARCH=amd64 and GOARCH=amd64p32 use 64bit wide registers.
However _64BIT itself is only defined when 6c is compiling for amd64 targets. The definition is elided for amd64p32 environments causing int, uint and other arch specific types to revert to their 32bit definitions.
LGTM=iant
R=iant, rsc, remyoudompheng
CC=golang-codereviews
https://golang.org/cl/72860046
gc does not report this as an error, but go/types does.
(I suspect that constructing a closure counts as a reference
to &all in gc's implementation).
This is not a tool bug, since the spec doesn't require
implementations to implement this check, but it does
illustrate that dialect variations are always a nuisance.
LGTM=rsc, bradfitz
R=bradfitz
CC=golang-codereviews, gri, rsc
https://golang.org/cl/73850043
Previously, passing a long duration to ParseDuration could result in
random, even negative, values.
LGTM=r
R=golang-codereviews, bradfitz, r
CC=golang-codereviews
https://golang.org/cl/72120043
CL 69340044 requires that syscall.SO_ERROR be defined on all unix like platforms. Add SO_ERROR to the list of dummy constants in sycall/net_nacl.go.
LGTM=bradfitz
R=iant, rsc, mikioh.mikioh, bradfitz
CC=golang-codereviews
https://golang.org/cl/73100043
If we report a leak, make sure we've waited long enough to be sure.
The new sleep regimen waits 1.05 seconds before failing; the old
one waited 0.005 seconds.
(The single linux/amd64 failure in this test feels more like a
timing problem than a leak. I don't want to spend time on it unless
we're sure.)
LGTM=bradfitz
R=bradfitz
CC=golang-codereviews
https://golang.org/cl/72630043
We provide amd64p32 implementations for md5 and sha1 so we need to exclude amd64p32 from the generic implementations in those packages.
Fixes build once CL 72360044 lands.
LGTM=agl, remyoudompheng
R=rsc, bradfitz, agl, remyoudompheng
CC=golang-codereviews
https://golang.org/cl/72460043
This fixes the following amd64p32 issue:
pkg/time/format.go:724: internal compiler error: twobitwalktype1: invalid initial alignment, Time
caused by the pointer zone ending on a 32-bit-aligned boundary.
LGTM=rsc
R=rsc, dave
CC=golang-codereviews
https://golang.org/cl/72270046
This code being buggy is the only explanation I can come up
with for issue 7325. It's probably not, but the only alternative
is a Windows kernel bug. Comment this out to see what breaks
or gets fixed.
Update #7325
LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/72590044
From the trace it appears that stackalloc is being
called with 0x1800 which is 6k = 4k + (StackSystem=2k).
Make StackSystem 4k too, to make stackalloc happy.
It's already 4k on windows/amd64.
TBR=khr
CC=golang-codereviews
https://golang.org/cl/72600043
It was using MOVL to pass a 64-bit argument
(concatenated framesize and argsize) to morestack11.
LGTM=dave, rsc
R=dave, rsc, iant
CC=golang-codereviews
https://golang.org/cl/72360044
There are at least 3 bugs:
1. g->stacksize accounting is broken during copystack/shrinkstack
2. stktop->free is not properly maintained during copystack/shrinkstack
3. stktop->free logic is broken:
we can have stktop->free==FixedStack,
and we will free it into stack cache,
but it actually comes from heap as the result of non-copying segment shrink
This shows as at least spurious races on race builders (maybe something else as well I don't know).
The idea behind the refactoring is to consolidate stacksize and
segment origin logic in stackalloc/stackfree.
Fixes#7490.
LGTM=rsc, khr
R=golang-codereviews, rsc, khr
CC=golang-codereviews
https://golang.org/cl/72440043
Recursive panics leave dangling Panic structs in g->panic stack.
At best it leads to a Defer leak and incorrect output on a subsequent panic.
At worst it arbitrary corrupts heap.
LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/72480043
One reason the sync.Pool finalizer test can fail is that
this function's ef1 contains uninitialized data that just
happens to point at some of the old pool. I've seen this cause
retention of a single pool cache line (32 elements) on arm.
Really we need liveness information for C functions, but
for now we can be more careful about data in long-lived
C functions that block.
LGTM=bradfitz, dvyukov
R=golang-codereviews, bradfitz, dvyukov
CC=golang-codereviews, iant, khr
https://golang.org/cl/72490043
Replaces CL 70000043.
Switch to the amd64p32 linker model if we are building under nacl/amd64p32.
No need to introduce linkarchinit() as 6a contains its own main() function.
LGTM=rsc
R=rsc, minux.ma
CC=golang-codereviews
https://golang.org/cl/72020043
Replaces CL 70000043.
Introduce linkarchinit() from cmd/ld.
For cmd/6g, switch to the amd64p32 linker model if we are building under nacl/amd64p32.
LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/71330045
This documents the status quo for most implementations,
with one exception: gc generates a run-time error for
constant but out-of-range indices when slicing a constant
string. See issue 7200 for a detailed discussion.
LGTM=r
R=r, rsc, iant, ken
CC=golang-codereviews
https://golang.org/cl/72160044
Instead, split the underlying storage in half and
free just half of it.
Shrinking without copying lets us reclaim storage used
by a previously profligate Go routine that has now blocked
inside some C code.
To shrink in place, we need all stacks to be a power of 2 in size.
LGTM=rsc
R=golang-codereviews, rsc
CC=golang-codereviews
https://golang.org/cl/69580044
This is a test case for CL 34680044.
Fixes#6333.
LGTM=bradfitz
R=golang-codereviews, bradfitz, minux.ma
CC=golang-codereviews
https://golang.org/cl/71230049
