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>
MIPS64 has 32 general purpose 64-bit integer registers (R0-R31), 32
64-bit floating point registers (F0-F31). Instructions are fixed-width,
and are 32-bit wide. Instructions are all in standard 1-, 2-, 3-operand
forms.
MIPS64-specific relocations are added. For this reason, test data of
cmd/newlink are regenerated.
No other changes are made to portable structures.
Branch delay slots are current filled with NOP instructions. The function
for instruction scheduling (try to fill the delay slot with a useful
instruction) is implemented but disabled for now.
Change-Id: Ic364999c7a33245260c1381fc26a2fa8972d38b3
Reviewed-on: https://go-review.googlesource.com/14442
Reviewed-by: Minux Ma <minux@golang.org>
This has been the root cause of a number of crashes caused by
fuzz throwing modem noise at the assembler, which in turn attempts
to print diagnostics but instead just gets crashes.
Fixes#12627.
Change-Id: I72c2da79d8eb240e1a37aa6140454c552b05e0f1
Reviewed-on: https://go-review.googlesource.com/14595
Reviewed-by: Ian Lance Taylor <iant@golang.org>
It is almost never set and Addr is large, so having the full struct
in the Prog wastes memory most of the time.
Before (on a 64-bit system):
$ sizeof -p cmd/internal/obj Addr Prog
Addr 80
Prog 376
$
After:
$ sizeof -p cmd/internal/obj Addr Prog
Addr 80
Prog 304
$
Change-Id: I491f201241f87543964a7d0f48b85830759be9d0
Reviewed-on: https://go-review.googlesource.com/10457
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
It shrinks Prog type from 448 bytes down to 376 bytes on amd64.
It also makes sense, because I don't know of any modern architecture
that have instructions which can write to two destinations, none of
which is a register (even x86 doesn't have such instructions).
Change-Id: I3061f1c9ac93d79ee2b92ecb9049641d0e0f6300
Reviewed-on: https://go-review.googlesource.com/10330
Reviewed-by: Aram Hăvărneanu <aram@mgk.ro>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Russ Cox <rsc@golang.org>
I was previously setting GOARM=arm5 (due to confusion with previously
seeing buildall.sh's temporary of "arm5" as a GOARCH and
misremembernig), but GOARM=arm5 was acting like GOARM=5 only on
accident. See https://go-review.googlesource.com/#/c/10023/
Instead, fail if GOARM is not a known value.
Change-Id: I9ba4fd7268df233d40b09f0431f37cd85a049847
Reviewed-on: https://go-review.googlesource.com/10024
Reviewed-by: Minux Ma <minux@golang.org>
Update #10652
This proposal deletes cmd/internal/ld.Biobuf and replaces all uses with
cmd/internal/obj.Biobuf. As cmd/internal/ld already imported cmd/internal/obj
there are no additional dependencies created.
Notes:
- ld.Boffset included more checks, so it was merged into obj.Boffset
- obj.Bflush was removed in 8d16253c90, so replaced all calls to
ld.Bflush, with obj.Biobuf.Flush.
- Almost all of this change was prepared with sed.
Change-Id: I814854d52f5729a5a40c523c8188e465246b88da
Reviewed-on: https://go-review.googlesource.com/9660
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Dave Cheney <dave@cheney.net>
This change applies CL 9365 to the copy of Biobuf in cmd/internal/obj.
In the process I discovered that some of the methods that should have been
checking the unget buffer before reading were not and it was probably just
dumb luck that we handn't hit these issues before; Bungetc is only used in
one place in cmd/internal/gc and only an unlikely code path.
Change-Id: Ifa0c5c08442e9fe951a5078c6e9ec77a8a4dc2ff
Reviewed-on: https://go-review.googlesource.com/9529
Reviewed-by: Daniel Morsing <daniel.morsing@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Dave Cheney <dave@cheney.net>
Run-TryBot: Dave Cheney <dave@cheney.net>
This is a follow up to rev 443a32e707 which reduces some of the
duplication between methods and functions that operate on obj.Biobuf.
obj.Biobuf has Flush and Write methods as well as helpers which duplicate
those methods, consolidate on the former and remove the latter.
Also, address a final comment from CL 9525.
Change-Id: I67deaf3a163bb489a9bb21bb39524785d7a2f6c5
Reviewed-on: https://go-review.googlesource.com/9527
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
There were 10 implementations of the trivial bool2int function, 9 of which
were the only thing in their file. Remove all of them in favor of one in
cmd/internal/obj.
Change-Id: I9c51d30716239df51186860b9842a5e9b27264d3
Reviewed-on: https://go-review.googlesource.com/9230
Reviewed-by: Ian Lance Taylor <iant@golang.org>
An interface{} is more in the spirit of the original union.
By my calculations, on 64-bit systems this reduces
Addr from 120 to 80 bytes, and Prog from 592 to 424 bytes.
Change-Id: I0d7b0981513c2a3c94c9ac76bb4f8816485b5a3c
Reviewed-on: https://go-review.googlesource.com/7744
Reviewed-by: Rob Pike <r@golang.org>
ARM64 (ARMv8) has 32 general purpose, 64-bit integer registers
(R0-R31), 32 64-bit scalar floating point registers (F0-F31), and
32 128-bit vector registers (unused, V0-V31).
R31 is either the stack pointer (RSP), or the zero register (ZR),
depending on the instruction. Note the distinction between the
hardware stack pointer, RSP, and the virtual stack pointer SP.
The (hardware) stack pointer must be 16-byte aligned at all times;
the RSP register itself must be aligned, offset(RSP) only has to
have natural alignment.
Instructions are fixed-width, and are 32-bit wide. ARM64 supports
ARMv7 too (32-bit ARM), but not in the same process. In general,
there is not much in common between 32-bit ARM and ARM64, it's a
new architecture.
All implementations have floating point instructions.
This change adds a Prog.To3 field analogous to Prog.To. It is used
by exclusive load/store instructions such as STLXR which read from
one register, and write to both a register and a memory address.
STLXRW R1, (R0), R3
This will store the word contained in R1 to the memory address
pointed by R0. R3 will be updated with the status result of the
store. It is used to implement atomic operations.
No other changes are made to the portable Prog and Addr structures.
Change-Id: Ie839029aa5265bbad35769d9689eca11e1c48c47
Reviewed-on: https://go-review.googlesource.com/7046
Reviewed-by: Russ Cox <rsc@golang.org>
Remove the per-achitecture formatter for Prog and replace it with
a global String method. Clean up and regularize the output. Update
tests affected by the format; some tests are made correct now when
they were broken before (and known to be).
Also, related: Change the encoding of the (R1+R2) syntax on ppc64
to be equivalent to (R1)(R2*1), which means it needs no special
handling.
Delete the now unused STRINGSZ constant.
Change-Id: I7f6654d11f80065f3914a3f19353f2f12edfe310
Reviewed-on: https://go-review.googlesource.com/6931
Reviewed-by: Russ Cox <rsc@golang.org>
Aconv is the pretty-printer for instruction opcodes like AMOVQ.
There was one for each architecture.
Make the space of A names have a different region for each architecture,
much as we did for the registers, so a single global Aconv function can
do the work. Each architecture registers its region as a slice of names
at a given offset.
The global names like CALL and JMP are now defined only once.
The A values are used for indexing tables, so make it easy to do the
indexing by making the offset maskable.
Remove a bunch of now-duplicated architecture-specific code.
Change-Id: Ib15647b7145a1c089e21e36543691a19e146b60e
Reviewed-on: https://go-review.googlesource.com/6620
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Rob Pike <r@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Today it's only recorded for C, but the Go version of the linker will need it.
Change-Id: I0de56d98e8f3f1b7feb830458c0934af367fd29a
Reviewed-on: https://go-review.googlesource.com/6333
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Minux Ma <minux@golang.org>
This is a follow-up to CL 6265. No behavior changes.
The diff was generated with eg, using template:
package p
import "fmt"
func before(a string) string { return fmt.Sprintf(a) }
func after(a string) string { return a }
Change-Id: I7b3bebf31be5cd1ae2233da06cb4502a3d73f092
Reviewed-on: https://go-review.googlesource.com/6269
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
ARM operands for MOVM have lists of registers: [R1,R2,R5-R8].
Handle them cleanly.
It was TYPE_CONST with special handling, which meant operand printing
didn't work right and the special handling was ugly. Add a new TYPE_REGLIST
for this case and it all gets cleaner.
Change-Id: I4a64f70fb9765e63cb636619a7a8553611bfe970
Reviewed-on: https://go-review.googlesource.com/6300
Run-TryBot: Rob Pike <r@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
Clean up the obj API by making Rconv (register pretty printer) a top-level
function. This means that Dconv (operand pretty printer) doesn't need
an Rconv argument.
To do this, we make the register numbers, which are arbitrary inside an
operand (obj.Addr), disjoint sets for each architecture. Each architecture
registers (ha) a piece of the space and then the global Rconv knows which
architecture-specific printer to use.
Clean up all the code that uses Dconv.
Now register numbers are large, so a couple of fields in Addr need to go
from int8 to int16 because they sometimes hold register numbers. Clean
up their uses, which meant regenerating the yacc grammars for the
assemblers. There are changes in this CL triggered by earlier changes
to yacc, which had not been run in this directory.
There is still cleanup to do in Addr, but we're getting closer to that being
easy to do.
Change-Id: I9290ebee013b62f7d24e886743ea5a6b232990ab
Reviewed-on: https://go-review.googlesource.com/6220
Reviewed-by: Russ Cox <rsc@golang.org>
It was just missing, and apparently always was.
Change-Id: I84c057bb0ec72940201075f3e6078262fe4bce05
Reviewed-on: https://go-review.googlesource.com/6120
Reviewed-by: Russ Cox <rsc@golang.org>
Each architecture had its own Dconv (operand printer) but the syntax is
close to uniform and the code overlap was considerable. Consolidate these
into a single top-level function. A similar but smaller unification is done
for Mconv ("Name" formatter) as well.
The signature is changed. The flag was unused so drop it. Add a
function argument, Rconv, that must be supplied by the caller.
TODO: A future change will unify Rconv as well and this argument
will go away.
Some formats changed, because of the automatic consistency
created by unification. For instance, 0(R1) always prints as (R1)
now, and foo+0(SB) is just foo(SB). Before, some made these
simplifications and some didn't; now they all do.
Update the asm tests that depend on the format.
Change-Id: I6e3310bc19814c0c784ff0b960a154521acd9532
Reviewed-on: https://go-review.googlesource.com/5920
Reviewed-by: Russ Cox <rsc@golang.org>
First draft of converted Go compiler, using rsc.io/c2go rev 83d795a.
Change-Id: I29f4c7010de07d2ff1947bbca9865879d83c32c3
Reviewed-on: https://go-review.googlesource.com/4851
Reviewed-by: Rob Pike <r@golang.org>
cmd/internal/obj reconverted using rsc.io/c2go rev 2a95256.
- Brings in new, more regular Prog, Addr definitions
- Add Prog* argument to oclass in liblink/asm[68].c, for c2go conversion.
- Update objwriter for change in TEXT size encoding.
- Merge 5a, 6a, 8a, 9a changes into new5a, new6a, new8a, new9a (by hand).
- Add +build ignore to cmd/asm/internal/{addr,arch,asm}, cmd/asm.
They need to be updated for the changes.
- Reenable verifyAsm in cmd/go.
- Reenable GOOBJ=2 mode by default in liblink.
All architectures build successfully again.
Change-Id: I2c845c5d365aa484b570476898171bee657b626d
Reviewed-on: https://go-review.googlesource.com/3963
Reviewed-by: Rob Pike <r@golang.org>
cmd/internal/obj reconverted using rsc.io/c2go rev 40275b8.
All Prog*s need Ctxt field set so that the printer can tell
which architecture the Prog belongs to.
Use ctxt.NewProg consistently for this.
Change-Id: Ic981b3d68f24931ffae74a772e83a3dc2fdf518a
Reviewed-on: https://go-review.googlesource.com/3152
Reviewed-by: Rob Pike <r@golang.org>
Using rsc.io/c2go repo revision 60c9302.
- Export a few symbols needed by assemblers.
- Implement Getgoroot etc directly, and add Getgoversion.
- Removes dependency on Go 1.4 go/build.
- Change magic history name <no name> to <pop>
The <pop> change requires adjustment to the liblink serializer.
Change-Id: If5fb52ac9e91d50805263070b3fc5cc05d8b7632
Reviewed-on: https://go-review.googlesource.com/3141
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
This CL adds the real cmd/internal/obj packages.
Collectively they correspond to the liblink library.
The conversion was done using rsc.io/c2go's run script
at rsc.io/c2go repo version 706fac7.
This is not the final conversion, just the first working draft.
There will be more updates, but this works well enough
to use with go tool objwriter and pass all.bash.
Change-Id: I9359e835425f995a392bb2fcdbebf29511477bed
Reviewed-on: https://go-review.googlesource.com/3046
Reviewed-by: Ian Lance Taylor <iant@golang.org>
