Russ Cox 1ac637c766 cmd/compile: recognize Syscall-like functions for liveness analysis ... Consider this code: func f(*int) func g() { p := new(int) f(p) } where f is an assembly function. In general liveness analysis assumes that during the call to f, p is dead in this frame. If f has retained p, p will be found alive in f's frame and keep the new(int) from being garbage collected. This is all correct and works. We use the Go func declaration for f to give the assembly function liveness information (the arguments are assumed live for the entire call). Now consider this code: func h1() { p := new(int) syscall.Syscall(1, 2, 3, uintptr(unsafe.Pointer(p))) } Here syscall.Syscall is taking the place of f, but because its arguments are uintptr, the liveness analysis and the garbage collector ignore them. Since p is no longer live in h once the call starts, if the garbage collector scans the stack while the system call is blocked, it will find no reference to the new(int) and reclaim it. If the kernel is going to write to *p once the call finishes, reclaiming the memory is a mistake. We can't change the arguments or the liveness information for syscall.Syscall itself, both for compatibility and because sometimes the arguments really are integers, and the garbage collector will get quite upset if it finds an integer where it expects a pointer. The problem is that these arguments are fundamentally untyped. The solution we have taken in the syscall package's wrappers in past releases is to insert a call to a dummy function named "use", to make it look like the argument is live during the call to syscall.Syscall: func h2() { p := new(int) syscall.Syscall(1, 2, 3, uintptr(unsafe.Pointer(p))) use(unsafe.Pointer(p)) } Keeping p alive during the call means that if the garbage collector scans the stack during the system call now, it will find the reference to p. Unfortunately, this approach is not available to users outside syscall, because 'use' is unexported, and people also have to realize they need to use it and do so. There is much existing code using syscall.Syscall without a 'use'-like function. That code will fail very occasionally in mysterious ways (see #13372). This CL fixes all that existing code by making the compiler do the right thing automatically, without any code modifications. That is, it takes h1 above, which is incorrect code today, and makes it correct code. Specifically, if the compiler sees a foreign func definition (one without a body) that has uintptr arguments, it marks those arguments as "unsafe uintptrs". If it later sees the function being called with uintptr(unsafe.Pointer(x)) as an argument, it arranges to mark x as having escaped, and it makes sure to hold x in a live temporary variable until the call returns, so that the garbage collector cannot reclaim whatever heap memory x points to. For now I am leaving the explicit calls to use in package syscall, but they can be removed early in a future cycle (likely Go 1.7). The rule has no effect on escape analysis, only on liveness analysis. Fixes #13372. Change-Id: I2addb83f70d08db08c64d394f9d06ff0a063c500 Reviewed-on: https://go-review.googlesource.com/18584 Reviewed-by: Ian Lance Taylor <iant@golang.org>		2016-01-14 01:16:45 +00:00
..
bench	encoding/base64: fix streaming decode of padding-free base64	2016-01-08 15:07:45 +00:00
bugs	test: migrate remaining tests to run.go	2014-12-22 22:41:34 +00:00
chan	Fix several out of date references to 4g/5g/6g/8g/9g.	2015-06-26 03:38:21 +00:00
ddd2.dir
dwarf
fixedbugs	cmd/compile: better modeling of escape across loop levels	2016-01-13 04:01:00 +00:00
import2.dir
import4.dir	test: adjust gccgo expected import errors	2015-10-07 14:37:44 +00:00
interface	cmd/internal/gc: improve "type *X has no field or method M" message	2015-05-07 16:21:57 +00:00
ken
method4.dir	cmd/gc: do not omit wrapper for expression (interface{...}).F	2014-01-07 13:26:48 +01:00
safe
stress	build: adjustments for move from src/pkg to src	2014-09-08 00:06:45 -04:00
syntax	cmd/compile: better syntax error recovery	2015-11-20 19:56:27 +00:00
64bit.go	cmd/gc: Error out on division by constant zero.	2013-01-30 20:21:08 +01:00
235.go
alias1.go	test: ensure all failing tests exit nonzero.	2013-02-12 13:17:49 -05:00
alias.go
append.go
args.go
assign1.go
assign.go	cmd/gc: prohibit short variable declarations containing duplicate symbols	2014-10-06 17:16:39 -04:00
bigalg.go	test: ensure all failing tests exit nonzero.	2013-02-12 13:17:49 -05:00
bigmap.go
blank1.go	cmd/compile: don't allow blank method declarations on builtins	2015-12-02 18:26:38 +00:00
blank.go	test: revert changes made for Go SSA interpreter test.	2013-10-08 14:36:20 -04:00
bom.go
bombad.go
bounds.go
chancap.go
chanlinear.go	runtime: test for linear enqueue/dequeue behavior	2014-12-08 22:18:17 +00:00
char_lit1.go
char_lit.go
clearfat.go	[dev.power64] 9g: fix under-zeroing in clearfat	2014-10-31 11:08:27 -04:00
closedchan.go
closure1.go	cmd/gc: capture variables by value	2015-01-29 13:07:30 +00:00
closure2.go	cmd/gc: fix capturing by value for range statements	2015-02-03 15:48:48 +00:00
closure.go
cmp6.go	cmd/gc: do not consider length zero arrays as comparable.	2014-01-31 00:30:56 +01:00
cmp.go	Fix several out of date references to 4g/5g/6g/8g/9g.	2015-06-26 03:38:21 +00:00
cmplx.go	cmd/gc: reject complex calls with mismatched argument types.	2013-03-11 22:55:14 +01:00
cmplxdivide1.go
cmplxdivide.c	test: comment the behavior and use of cmplxdivide*	2015-01-15 00:00:06 +00:00
cmplxdivide.go	test: comment the behavior and use of cmplxdivide*	2015-01-15 00:00:06 +00:00
complit1.go	cmd/internal/gc: accept map literals with omitted key type	2015-06-04 02:31:38 +00:00
complit.go
compos.go
const1.go	test: match gccgo error messages	2013-12-12 17:18:12 -08:00
const2.go
const3.go
const4.go	all: link to https instead of http	2015-07-11 14:36:33 +00:00
const5.go	all: link to https instead of http	2015-07-11 14:36:33 +00:00
const6.go	test: match gccgo error strings.	2013-06-26 18:05:02 +02:00
const.go	cmd/compile: allow huge rsh in constants arithmetic	2015-08-21 20:27:22 +00:00
convert1.go
convert3.go
convert.go
convlit1.go
convlit.go	cmd/internal/gc: unsafe.Pointer constants may only be converted to uintptr	2015-05-07 23:54:28 +00:00
convT2X.go
copy.go	test: ensure all failing tests exit nonzero.	2013-02-12 13:17:49 -05:00
crlf.go
ddd1.go
ddd2.go
ddd.go
decl.go	test: ensure all failing tests exit nonzero.	2013-02-12 13:17:49 -05:00
declbad.go
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
deferprint.out
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
env.go
eof1.go
eof.go
errchk	Fix several out of date references to 4g/5g/6g/8g/9g.	2015-06-26 03:38:21 +00:00
escape2.go	cmd/compile: better modeling of escape across loop levels	2016-01-13 04:01:00 +00:00
escape2n.go	cmd/compile: better modeling of escape across loop levels	2016-01-13 04:01:00 +00:00
escape3.go
escape4.go	cmd/internal/gc: transitive inlining	2015-02-26 17:36:00 +00:00
escape5.go	cmd/internal/gc: move check for large-hence-heap-allocated types into escape analysis	2015-05-22 02:13:54 +00:00
escape_array.go	cmd/internal/gc: move check for large-hence-heap-allocated types into escape analysis	2015-05-22 02:13:54 +00:00
escape_calls.go	cmd/internal/gc: make indirect calls properly escape-y	2015-05-22 01:36:11 +00:00
escape_closure.go	cmd/internal/gc: improve flow of input params to output params	2015-05-01 13:47:20 +00:00
escape_field.go	cmd/internal/gc: improve flow of input params to output params	2015-05-01 13:47:20 +00:00
escape_iface.go	cmd/compile: add case for ODOTTYPE to escwalk	2015-07-30 17:39:44 +00:00
escape_indir.go	cmd/internal/gc: improve flow of input params to output params	2015-05-01 13:47:20 +00:00
escape_level.go	cmd/internal/gc: improve flow of input params to output params	2015-05-01 13:47:20 +00:00
escape_map.go	test: add tests for escape analysis of interface conversions	2015-03-28 16:15:27 +00:00
escape_param.go	cmd/internal/gc: improve flow of input params to output params	2015-05-01 13:47:20 +00:00
escape_slice.go	cmd/internal/gc: extend escape analysis to pointers in slices	2015-05-18 15:34:39 +00:00
escape_struct_param1.go	cmd/internal/gc: improve flow of input params to output params	2015-05-01 13:47:20 +00:00
escape_struct_param2.go	cmd/internal/gc: improve flow of input params to output params	2015-05-01 13:47:20 +00:00
escape_struct_return.go	cmd/internal/gc: improve flow of input params to output params	2015-05-01 13:47:20 +00:00
escape.go	test: ensure all failing tests exit nonzero.	2013-02-12 13:17:49 -05:00
fibo.go	Fix whitespace (use blanks consistently).	2014-12-08 22:22:58 +00:00
finprofiled.go	runtime: fix finalization and profiling of tiny allocations	2015-11-03 18:57:18 +00:00
float_lit2.go	test: fix two typos in float_lit2.go	2014-05-21 17:19:12 -04:00
float_lit3.go	test/float_lit2.go: rewrite to test values near boundaries	2014-05-21 17:12:06 -04:00
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
func1.go	cmd/gc: ensure unique parameter and result names in function types	2013-03-15 15:24:13 -04:00
func2.go
func3.go
func4.go
func5.go
func6.go	Fix several out of date references to 4g/5g/6g/8g/9g.	2015-06-26 03:38:21 +00:00
func7.go	Fix several out of date references to 4g/5g/6g/8g/9g.	2015-06-26 03:38:21 +00:00
func8.go	test: use go:noinline consistently	2015-11-03 02:01:34 +00:00
func.go
funcdup2.go	test: match gccgo error messages	2013-12-12 17:18:12 -08:00
funcdup.go	test: match gccgo error messages	2013-12-12 17:18:12 -08:00
gc1.go
gc2.go	test: check for build constraints only upto the first blank line	2015-02-06 05:36:26 +00:00
gc.go
gcstring.go	runtime: fix empty string handling in garbage collector	2014-03-11 23:58:39 -04:00
goprint.go	test: make goprint.go wait longer for go its routine to execute	2013-04-12 16:04:19 -07:00
goprint.out
goto.go	Revert "cmd/internal/gc: ignore declarations of types for goto validation"	2015-05-15 16:35:49 +00:00
heapsampling.go	test: really force heap profile update in heapsampling.go	2015-11-12 18:32:13 +00:00
helloworld.go
helloworld.out
if.go
import1.go	test: match gccgo import error messages	2013-12-12 19:02:11 -08:00
import2.go
import4.go
import5.go
import.go
index0.go
index1.go
index2.go
index.go	Fix several out of date references to 4g/5g/6g/8g/9g.	2015-06-26 03:38:21 +00:00
indirect1.go
indirect.go
init1.go	test: deflake init1.go test, tighten its bounds	2015-02-13 22:13:56 +00:00
init.go
initcomma.go
initialize.go
initializerr.go
initloop.go	cmd/compile: use []*Node instead of NodeList in sinit	2015-09-05 02:25:01 +00:00
inline.go	cmd/compile: add support for a go:noinline directive	2015-10-29 23:16:27 +00:00
int_lit.go
intcvt.go
iota.go
label1.go
label.go
linkmain_run.go	test: fix linkmain test	2015-12-17 23:36:13 +00:00
linkmain.go	cmd/link: reject non-package main toplevel.a file, remove dead code	2015-12-17 20:59:51 +00:00
linkx_run.go	cmd/link: detect -X setting non-string variable	2015-06-29 20:28:36 +00:00
linkx.go	cmd/link: detect -X setting non-string variable	2015-06-29 20:28:36 +00:00
literal.go	test: ensure all failing tests exit nonzero.	2013-02-12 13:17:49 -05:00
live1.go	cmd/gc: correct liveness for fat variables	2014-02-15 10:58:55 -05:00
live2.go	cmd/gc: allocate non-escaping maps on stack	2015-02-12 09:53:52 +00:00
live_syscall.go	cmd/compile: recognize Syscall-like functions for liveness analysis	2016-01-14 01:16:45 +00:00
live.go	test: add -update_errors flag to run script	2015-04-10 11:33:42 +00:00
mallocfin.go
map1.go
map.go	test/mapnan.go: add regression test for non-empty interfaces.	2014-08-06 17:02:55 -04:00
maplinear.go	test: make maplinear more robust	2014-10-27 18:59:02 -04:00
method1.go
method2.go	cmd/gc: fix method values whose receiver is an unnamed interface.	2013-08-29 10:00:58 +02:00
method3.go
method4.go
method5.go	cmd/gc: implement method values	2013-03-20 17:11:09 -04:00
method.go	test: a number of fixes.	2013-02-11 18:20:52 -05:00
named1.go	cmd/gc: comma-ok assignments produce untyped bool as 2nd result	2014-08-11 16:11:55 -07:00
named.go
nil.go	test: ensure all failing tests exit nonzero.	2013-02-12 13:17:49 -05:00
nilcheck.go	cmd/gc: optimize existence-only map lookups	2015-01-07 22:36:06 +00:00
nilptr2.go	test: revert changes made for Go SSA interpreter test.	2013-10-08 14:36:20 -04:00
nilptr3.go	test: fix nosplit.go, fixedbugs/issue11656.go and skip two tests for mips64{,le}	2015-11-12 04:52:31 +00:00
nilptr4.go	cmd/gc: fix bad checknil with ints on 32 bit compilers	2014-02-26 12:25:13 -08:00
nilptr.go	test/nilptr: add more tests	2013-09-05 23:06:34 -04:00
nosplit.go	cmd/internal/obj, cmd/link, runtime: increase stack limit to accommodate larger frames on ppc64x	2015-11-12 22:32:16 +00:00
nul1.go
parentype.go
peano.go
print.go	runtime: move built-in print routines to go.	2014-07-31 13:48:48 -07:00
print.out	runtime: move built-in print routines to go.	2014-07-31 13:48:48 -07:00
printbig.go
printbig.out
range.go	cmd/gc: implement 'for range x {'	2014-07-16 19:27:10 -04:00
recover1.go
recover2.go
recover3.go	tests: remove two misuses of nil pointers	2013-08-15 11:51:04 -04:00
recover4.go	test: move allocation before munmap in recover4	2015-09-16 08:51:48 +00:00
recover.go	test: add more cases to recover.go	2014-10-22 08:06:15 -07:00
rename1.go
rename.go	test: ensure all failing tests exit nonzero.	2013-02-12 13:17:49 -05:00
reorder2.go	test: use go:noinline consistently	2015-11-03 02:01:34 +00:00
reorder.go	test: a number of fixes.	2013-02-11 18:20:52 -05:00
return.go	test: add cases to return.go that gccgo got wrong	2013-08-07 11:31:01 -07:00
rotate0.go	test: re-enable rotate tests	2015-05-28 19:40:58 +00:00
rotate1.go	test: re-enable rotate tests	2015-05-28 19:40:58 +00:00
rotate2.go	test: re-enable rotate tests	2015-05-28 19:40:58 +00:00
rotate3.go	test: re-enable rotate tests	2015-05-28 19:40:58 +00:00
rotate.go
run.go	misc/cgo/stdio: reenable tests	2015-12-05 21:24:30 +00:00
rune.go
runtime.go
shift1.go	test: avoid "declared but not used" errors in shift1.go	2014-07-20 12:25:24 -07:00
shift2.go	test: add shift expression incorrectly rejected by gccgo.	2013-06-25 08:06:34 +02:00
sieve.go
sigchld.go	test: skip SIGCHLD test on Plan 9	2014-01-29 09:28:23 +01:00
sigchld.out
simassign.go
sinit_run.go	all: retire architecture letter in file names, public API	2015-05-21 17:32:17 +00:00
sinit.go	cmd/compile: allow static init for unsafe.Pointer(&x) where x is global	2015-07-07 21:51:57 +00:00
sizeof.go	test: correct sizeof.go.	2013-06-02 19:10:11 +02:00
slice3.go	cmd/gc, runtime: treat slices and strings like pointers in garbage collection	2014-08-25 14:38:19 -04:00
slice3err.go	test: match gccgo error messages	2013-12-12 17:18:12 -08:00
slicecap.go	cmd/gc, runtime: treat slices and strings like pointers in garbage collection	2014-08-25 14:38:19 -04:00
sliceopt.go	cmd/internal/gc: optimize slice + write barrier	2015-05-13 19:20:39 +00:00
solitaire.go
stack.go
string_lit.go	test: add []rune case to string_lit.go	2013-12-12 17:17:02 -08:00
stringrange.go
struct0.go
switch2.go	cmd/compile: address several more 1.6 TODOs in parser	2015-11-21 07:21:23 +00:00
switch3.go
switch4.go	cmd/gc: disallow fallthrough in final case of switch	2013-03-15 00:35:09 -04:00
switch.go	cmd/gc: disallow fallthrough in final case of switch	2013-03-15 00:35:09 -04:00
tinyfin.go	runtime: fix finalization and profiling of tiny allocations	2015-11-03 18:57:18 +00:00
torture.go	cmd/8g: don't allocate a register early for cap(CHAN).	2014-07-01 09:20:51 +02:00
turing.go
typecheck.go	cmd/gc: silence assignment errors to undefined symbols	2014-01-03 21:03:20 +01:00
typecheckloop.go	cmd/compile: convert typecheck_stack to []*Node	2015-09-06 23:50:51 +00:00
typeswitch1.go
typeswitch2.go
typeswitch3.go
typeswitch.go
undef.go
utf.go
varerr.go
varinit.go
writebarrier.go	cmd/internal/gc: add missing write barrier in append(x, BigStructWithPointers)	2015-05-19 15:28:29 +00:00
zerodivide.go	test: ensure all failing tests exit nonzero.	2013-02-12 13:17:49 -05:00