Given
type Outer struct {
*Inner
...
}
the compiler generates the implementation of (*Outer).M dispatching to
the embedded Inner. The implementation is logically:
func (p *Outer) M() {
(p.Inner).M()
}
but since the only change here is the replacement of one pointer
receiver with another, the actual generated code overwrites the
original receiver with the p.Inner pointer and then jumps to the M
method expecting the *Inner receiver.
During reflect.Value.Call, we create an argument frame and the
associated data structures to describe it to the garbage collector,
populate the frame, call reflect.call to run a function call using
that frame, and then copy the results back out of the frame. The
reflect.call function does a memmove of the frame structure onto the
stack (to set up the inputs), runs the call, and the memmoves the
stack back to the frame structure (to preserve the outputs).
Originally reflect.call did not distinguish inputs from outputs: both
memmoves were for the full stack frame. However, in the case where the
called function was one of these wrappers, the rewritten receiver is
almost certainly a different type than the original receiver. This is
not a problem on the stack, where we use the program counter to
determine the type information and understand that during (*Outer).M
the receiver is an *Outer while during (*Inner).M the receiver in the
same memory word is now an *Inner. But in the statically typed
argument frame created by reflect, the receiver is always an *Outer.
Copying the modified receiver pointer off the stack into the frame
will store an *Inner there, and then if a garbage collection happens
to scan that argument frame before it is discarded, it will scan the
*Inner memory as if it were an *Outer. If the two have different
memory layouts, the collection will intepret the memory incorrectly.
Fix by only copying back the results.
Fixes#7725.
LGTM=khr
R=khr
CC=dave, golang-codereviews
https://golang.org/cl/85180043
It turns out there is a relatively common pattern that relies on
inverted channel semaphore:
gate := make(chan bool, N)
for ... {
// limit concurrency
gate <- true
go func() {
foo(...)
<-gate
}()
}
// join all goroutines
for i := 0; i < N; i++ {
gate <- true
}
So handle synchronization on inverted semaphores with cap>1.
Fixes#7718.
LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/84880046
This code tests linkmode == LinkExternal but is only invoked
by the compiler/assembler, not the linker.
Update #7164
LGTM=rsc
R=rsc, dave
CC=golang-codereviews
https://golang.org/cl/85080043
Defers generated from cgo lie to us about their argument layout.
Mark those defers as not copyable.
CL 83820043 contains an additional test for this code and should be
checked in (and enabled) after this change is in.
Fixes bug 7695.
LGTM=rsc
R=golang-codereviews, rsc
CC=golang-codereviews
https://golang.org/cl/84740043
Iterate the right number of times in arrays and channels.
Handle channels with zero-sized objects in them.
Output longer type names if we have them.
Compute argument offset correctly.
LGTM=rsc
R=golang-codereviews, rsc
CC=golang-codereviews
https://golang.org/cl/82980043
Also makes ErrWriteToConnected more appropriate; it's used
not only UDPConn operations but UnixConn operations.
Update #4856
LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/84800044
The prefix was not uniformly applied and is probably better
left off for using with OpError.
Update #4856
LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/84660046
Takes advantage of CL 83740044, to optimize map[string] lookup
from []byte key.
Deletes code.
No conditional check for gccgo, since Ian plans to add this
to gccgo before GCC 4.10 (Go 1.3).
benchmark old ns/op new ns/op delta
BenchmarkReadMIMEHeader 6066 5086 -16.16%
benchmark old allocs new allocs delta
BenchmarkReadMIMEHeader 12 12 +0.00%
benchmark old bytes new bytes delta
BenchmarkReadMIMEHeader 1317 1317 +0.00%
Update #3512
LGTM=rsc
R=rsc, dave
CC=golang-codereviews, iant
https://golang.org/cl/84230043
Superficial inconsistencies that trigger warnings in
Plan 9. Small enough to be considered trivial and
seemingly benign outside of the Plan 9 environment.
LGTM=iant
R=golang-codereviews, 0intro, iant
CC=golang-codereviews
https://golang.org/cl/73460043
If an error happens on a connection, server goroutine can call b.Logf
after benchmark finishes.
So join both client and server goroutines.
Update #7718
LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/84750047
I have no idea what this code is for, but it pretty
clearly needs to be uint64, not uint32.
LGTM=aram
R=0intro, aram
CC=golang-codereviews
https://golang.org/cl/84410043
Native Client forbids jumps/calls to arbitrary locations and
enforces a particular alignement, which makes the Duff's device
ineffective.
LGTM=khr
R=rsc, dave, khr
CC=golang-codereviews
https://golang.org/cl/84400043
Trying to make GODEBUG=gcdead=1 work with liveness
and in particular ambiguously live variables.
1. In the liveness computation, mark all ambiguously live
variables as live for the entire function, except the entry.
They are zeroed directly after entry, and we need them not
to be poisoned thereafter.
2. In the liveness computation, compute liveness (and deadness)
for all parameters, not just pointer-containing parameters.
Otherwise gcdead poisons untracked scalar parameters and results.
3. Fix liveness debugging print for -live=2 to use correct bitmaps.
(Was not updated for compaction during compaction CL.)
4. Correct varkill during map literal initialization.
Was killing the map itself instead of the inserted value temp.
5. Disable aggressive varkill cleanup for call arguments if
the call appears in a defer or go statement.
6. In the garbage collector, avoid bug scanning empty
strings. An empty string is two zeros. The multiword
code only looked at the first zero and then interpreted
the next two bits in the bitmap as an ordinary word bitmap.
For a string the bits are 11 00, so if a live string was zero
length with a 0 base pointer, the poisoning code treated
the length as an ordinary word with code 00, meaning it
needed poisoning, turning the string into a poison-length
string with base pointer 0. By the same logic I believe that
a live nil slice (bits 11 01 00) will have its cap poisoned.
Always scan full multiword struct.
7. In the runtime, treat both poison words (PoisonGC and
PoisonStack) as invalid pointers that warrant crashes.
Manual testing as follows:
- Create a script called gcdead on your PATH containing:
#!/bin/bash
GODEBUG=gcdead=1 GOGC=10 GOTRACEBACK=2 exec "$@"
- Now you can build a test and then run 'gcdead ./foo.test'.
- More importantly, you can run 'go test -short -exec gcdead std'
to run all the tests.
Fixes#7676.
While here, enable the precise scanning of slices, since that was
disabled due to bugs like these. That now works, both with and
without gcdead.
Fixes#7549.
LGTM=khr
R=khr
CC=golang-codereviews
https://golang.org/cl/83410044
runtime.Version() requires a trailing "+" when
tree had local modifications at time of build.
Fixes#7701
LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/84040045
The garbage collector poison pointers
(0x6969696969696969 and 0x6868686868686868)
are malformed addresses on amd64.
That is, they are not 48-bit addresses sign extended
to 64 bits. This causes a different kind of hardware fault
than the usual 'unmapped page' when accessing such
an address, and OS X 10.9.2 sends the resulting SIGSEGV
incorrectly, making it look like it was user-generated
rather than kernel-generated and does not include the
faulting address. This means that in GODEBUG=gcdead=1
mode, if there is a bug and something tries to dereference
a poisoned pointer, the runtime delivers the SIGSEGV to
os/signal and returns to the faulting code, which faults
again, causing the process to hang instead of crashing.
Fix by rewriting "user-generated" SIGSEGV on OS X to
look like a kernel-generated SIGSEGV with fault address
0xb01dfacedebac1e.
I chose that address because (1) when printed in hex
during a crash, it is obviously spelling out English text,
(2) there are no current Google hits for that pointer,
which will make its origin easy to find once this CL
is indexed, and (3) it is not an altogether inaccurate
description of the situation.
Add a test. Maybe other systems will break too.
LGTM=khr
R=golang-codereviews, khr
CC=golang-codereviews, iant, ken
https://golang.org/cl/83270049
Delaying the runtime.throw until here will print more information.
In particular it will print the signal and code values, which means
it will show the fault address.
The canpanic checks were added recently, in CL 75320043.
They were just not added in exactly the right place.
LGTM=iant
R=dvyukov, iant
CC=golang-codereviews
https://golang.org/cl/83980043
Brad has been asking for this for a while.
I have resisted because I wanted to find a more general way to
do this, one that would keep the performance of code introducing
variables the same as the performance of code that did not.
(See golang.org/issue/3512#c20).
I have not found the more general way, and recent changes to
remove ambiguously live temporaries have blown away the
property I was trying to preserve, so that's no longer a reason
not to make the change.
Fixes#3512.
LGTM=iant
R=iant
CC=bradfitz, golang-codereviews, khr, r
https://golang.org/cl/83740044
Cuts hello world by 70kB, because we don't write
those names into the symbol table.
Update #6853
LGTM=khr
R=khr
CC=golang-codereviews
https://golang.org/cl/80370045
This is just testing the status quo, so that any future attempt
to change it will make the test break and redirect the person
making the change to look at issue 6027.
Fixes#6027.
LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/83930046
Supports all the current GNU tar sparse formats, including the
old GNU format and the GNU PAX format versions 0.0, 0.1, and 1.0.
Fixes#3864.
LGTM=rsc
R=golang-codereviews, dave, gobot, dsymonds, rsc
CC=golang-codereviews
https://golang.org/cl/64740043
The software floating point runs with m->locks++
to avoid being preempted; recognize this case in panic
and undo it so that m->locks is maintained correctly
when panicking.
Fixes#7553.
LGTM=dvyukov
R=golang-codereviews, dvyukov
CC=golang-codereviews
https://golang.org/cl/84030043
The old limit of 5 was chosen because we didn't actually know how
many bytes of arguments there were; 5 was a halfway point between
printing some useful information and looking ridiculous.
Now we know how many bytes of arguments there are, and we stop
the printing when we reach that point, so the "looking ridiculous" case
doesn't happen anymore: we only print actual argument words.
The cutoff now serves only to truncate very long (but real) argument lists.
In multiple debugging sessions recently (completely unrelated bugs)
I have been frustrated by not seeing more of the long argument lists:
5 words is only 2.5 interface values or strings, and not even 2 slices.
Double the max amount we'll show.
LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews, iant, r
https://golang.org/cl/83850043
The data field is the generic array that acts as a standin
for the keys and values arrays for the generic runtime code.
We want to substitute the keys and values arrays for the data
array, not just add keys and values in addition to it.
LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/81160044
Darwin 10.6 (gcc 4.2) and some older versions of gcc default to C90 mode, not C99 mode. Silence the warning.
LGTM=aram, iant
R=golang-codereviews, aram, iant
CC=golang-codereviews
https://golang.org/cl/83090050
