During a cgo call, the stack can be copied. This copy invalidates
the pointer that cgo has into the return value area. To fix this
problem, pass the address of the location containing the stack
top value (which is in the G struct). For cgo functions which
return values, read the stktop before and after the cgo call to
compute the adjustment necessary to write the return value.
Fixes#8771
LGTM=iant, rsc
R=iant, rsc, khr
CC=golang-codereviews
https://golang.org/cl/144130043
Normally, the caller to runtime.entersyscall() must not return before
calling runtime.exitsyscall(), lest g->syscallsp become a dangling
pointer. runtime.cgocallbackg() violates this constraint. To work around
this, save g->syscallsp and g->syscallpc around cgo->Go callbacks, then
restore them after calling runtime.entersyscall(), which restores the
syscall stack frame pointer saved by cgocall. This allows the GC to
correctly trace a goroutine that is currently returning from a
Go->cgo->Go chain.
This also adds a check to proc.c that panics if g->syscallsp is clearly
invalid. It is not 100% foolproof, as it will not catch a case where the
stack was popped then pushed back beyond g->syscallsp, but it does catch
the present cgo issue and makes existing tests fail without the bugfix.
Fixes#7978.
LGTM=dvyukov, rsc
R=golang-codereviews, dvyukov, minux, bradfitz, iant, gobot, rsc
CC=golang-codereviews, rsc
https://golang.org/cl/131910043
Now it's two allocations. I don't see much downside to that,
since the two pieces were in different cache lines anyway.
Rename 'conservative' to 'cgo_conservative_type' and make
clear that _cgo_allocate is the only allowed user.
This depends on CL 141490043, which removes the other
use of conservative (in defer).
LGTM=dvyukov, iant
R=khr, dvyukov, iant
CC=golang-codereviews, rlh
https://golang.org/cl/139610043
If you write:
var x = 3
then the compiler arranges for x to be initialized in the linker
with an actual 3 from the data segment, rather than putting
x in the bss and emitting init-time "x = 3" assignment code.
If you write:
var y = x
var x = 3
then the compiler is clever and treats this the same as if
the code said 'y = 3': they both end up in the data segment
with no init-time assignments.
If you write
var y = x
var x int
then the compiler was treating this the same as if the
code said 'x = 0', making both x and y zero and avoiding
any init-time assignment.
This copying optimization to avoid init-time assignment of y
is incorrect if 'var x int' doesn't mean 'x = 0' but instead means
'x is initialized in C or assembly code'. The program ends up
with 'y = 0' instead of 'y = the value specified for x in that other code'.
Disable the propagation if there is no initializer for x.
This comes up in some uses of cgo, because cgo generates
Go globals that are initialized in accompanying C files.
Fixes#7665.
LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/93200044
The old approach to determining whether "name" was a type, constant,
or expression was to compile the C program
name;
and scan the errors and warnings generated by the compiler.
This requires looking for specific substrings in the errors and warnings,
which ties the implementation to specific compiler versions.
As compilers change their errors or drop warnings, cgo breaks.
This happens slowly but it does happen.
Clang in particular (now required on OS X) has a significant churn rate.
The new approach compiles a slightly more complex program
that is either valid C or not valid C depending on what kind of
thing "name" is. It uses only the presence or absence of an error
message on a particular line, not the error text itself. The program is:
// error if and only if name is undeclared
void f1(void) { typeof(name) *x; }
// error if and only if name is not a type
void f2(void) { name *x; }
// error if and only if name is not an integer constant
void f3(void) { enum { x = (name)*1 }; }
I had not been planning to do this until Go 1.3, because it is a
non-trivial change, but it fixes a real Xcode 5 problem in Go 1.2,
and the new code is easier to understand than the old code.
It should be significantly more robust.
Fixes#6596.
Fixes#6612.
R=golang-dev, r, james, iant
CC=golang-dev
https://golang.org/cl/15070043
Because we can, and because it otherwise might crash
the program if we think we're out of memory.
Fixes#6390.
R=golang-dev, iant, minux.ma
CC=golang-dev
https://golang.org/cl/13345048
This is not quite what that issue reports,
because this does not involve a DLL.
But I wanted to make sure this much was working.
Update #4339
R=golang-dev, minux.ma
CC=golang-dev
https://golang.org/cl/13653043
* Add a new kind of Name, "fpvar" which stands for function pointer variable
* When walking the AST, find functions used as expressions and create a new Name object for them
* Track functions which are only used in expr contexts, and avoid generating bridge code for them
R=golang-dev, minux.ma, fullung, rsc, iant
CC=golang-dev
https://golang.org/cl/9835047
This change removes processing of #cgo directives from cmd/cgo,
pushing the onus back on cmd/go to pass all necessary flags.
Fixes#5224. See comments for rationale.
R=golang-dev, iant, r
CC=golang-dev
https://golang.org/cl/8610044
Some variables declared in C could end up as undefined symbols
in the final binary and have null address.
Fixes#5114.
Fixes#5227.
R=golang-dev, iant, ajstarks, dave, r
CC=golang-dev
https://golang.org/cl/8602044
The ARM implementation of runtime.cgocallback_gofunc diverged
from the calling convention by leaving a word of garbage at
the top of the stack and storing the return PC above the
locals. This change stores the return PC at the top of the
stack and removes the save area above the locals.
Update #5124
This CL fixes first part of the ARM issues and added the unwind test.
R=golang-dev, bradfitz, minux.ma, cshapiro, rsc
CC=golang-dev
https://golang.org/cl/7728045
* Separate internal and external LockOSThread, for cgo safety.
* Show goroutine that made faulting cgo call.
* Never start a panic due to a signal caused by a cgo call.
Fixes#3774.
Fixes#3775.
Fixes#3797.
R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/7228081
Always process the DWARF info, even when the const value is determined
using the debug data block. This ensures that the injected enum is
removed and future loads of the same constant do not trigger
inconsistent definitions.
Add tests for issues 2470 and 4054.
Fixes#4054.
R=golang-dev, fullung, dave, rsc, minux.ma
CC=golang-dev
https://golang.org/cl/6501101
This CL adds a step to the build procedure for cgo programs. It uses 'ld -r'
to combine all gcc compiled object file and generate a relocatable object file
for our ld. Additionally, this linking step will combine some static linking
gcc library into the relocatable object file, so that we can use libgcc,
libmingwex and libmingw32 without problem.
Fixes#3261.
Fixes#1741.
Added a testcase for linking in libgcc.
TODO:
1. still need to fix the INDIRECT_SYMBOL_LOCAL problem on Darwin/386.
2. still need to enable the libgcc test on Linux/ARM, because 5l can't deal
with thumb libgcc.
Tested on Darwin/amd64, Darwin/386, FreeBSD/amd64, FreeBSD/386, Linux/amd64,
Linux/386, Linux/ARM, Windows/amd64, Windows/386
R=iant, rsc, bradfitz, coldredlemur
CC=golang-dev
https://golang.org/cl/5822049
Allocate Defer on stack during cgo calls, as suggested
by dvyukov. Also includes some comment corrections.
benchmark old,ns/op new,ns/op
BenchmarkCgoCall 669 330
(Intel Xeon CPU 1.80GHz * 4, Linux 386)
R=dvyukov, rsc
CC=golang-dev
https://golang.org/cl/4910041
The new gotest ignores Test functions outside *_test.go files
(the old shell script allowed them), so replace one clumsy hack
with another.
The root problem is that the package makefiles only know
how to run cgo for source files in the package proper, not
for test files. Making it work for test files is probably more
trouble than it's worth.
R=bradfitz
CC=golang-dev
https://golang.org/cl/4452060
* Change use of m->g0 stack (aka scheduler stack).
* Provide runtime.mcall(f) to invoke f() on m->g0 stack.
* Replace scheduler loop entry with runtime.mcall(schedule).
Runtime.mcall eliminates the need for fake scheduler states that
exist just to run a bit of code on the m->g0 stack
(Grecovery, Gstackalloc).
The elimination of the scheduler as a loop that stops and
starts using gosave and gogo fixes a bad interaction with the
way cgo uses the m->g0 stack. Cgo runs external (gcc-compiled)
C functions on that stack, and then when calling back into Go,
it sets m->g0->sched.sp below the added call frames, so that
other uses of m->g0's stack will not interfere with those frames.
Unfortunately, gogo (longjmp) back to the scheduler loop at
this point would end up running scheduler with the lower
sp, which no longer points at a valid stack frame for
a call to scheduler. If scheduler then wrote any function call
arguments or local variables to where it expected the stack
frame to be, it would overwrite other data on the stack.
I realized this possibility while debugging a problem with
calling complex Go code in a Go -> C -> Go cgo callback.
This wasn't the bug I was looking for, it turns out, but I believe
it is a real bug nonetheless. Switching to runtime.mcall, which
only adds new frames to the stack and never jumps into
functions running in existing ones, fixes this bug.
* Move cgo-related code out of proc.c into cgocall.c.
* Add very large comment describing cgo call sequences.
* Simpilify, regularize cgo function implementations and names.
* Add test suite as misc/cgo/test.
Now the Go -> C path calls cgocall, which calls asmcgocall,
and the C -> Go path calls cgocallback, which calls cgocallbackg.
The shuffling, which affects mainly the callback case, moves
most of the callback implementation to cgocallback running
on the m->curg stack (not the m->g0 scheduler stack) and
only while accounted for with $GOMAXPROCS (between calls
to exitsyscall and entersyscall).
The previous callback code did not block in startcgocallback's
approximation to exitsyscall, so if, say, the garbage collector
were running, it would still barge in and start doing things
like call malloc. Similarly endcgocallback's approximation of
entersyscall did not call matchmg to kick off new OS threads
when necessary, which caused the bug in issue 1560.
Fixes#1560.
R=iant
CC=golang-dev
https://golang.org/cl/4253054
