We also rename the constants related to unsafe-points: currently, they
follow the same naming scheme as the PCDATA table indexes, but are not
PCDATA table indexes.
For #59670.
Change-Id: I06529fecfae535be5fe7d9ac56c886b9106c74fd
Reviewed-on: https://go-review.googlesource.com/c/go/+/485497
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Austin Clements <austin@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
With the switch to the register ABI, we now generate wrapper
functions for go statements in many cases. A new goroutine's start
PC now points to the wrapper function. This does not affect
execution, but the runtime tracer uses the start PC and the
function name as the name/label of that goroutine. If the start
function is a named function, using the name of the wrapper loses
that information. Furthur, the tracer's goroutine view groups
goroutines by start PC. For multiple go statements with the same
callee, they are grouped together. With the wrappers, which is
context-dependent as it is a closure, they are no longer grouped.
This CL fixes the problem by providing the underlying unwrapped
PC for tracing. The compiler emits metadata to link the unwrapped
PC to the wrapper function. And the runtime reads that metadata
and record that unwrapped PC for tracing.
(This doesn't work for shared buildmode. Unfortunate.)
TODO: is there a way to test?
Fixes#50622.
Change-Id: Iaa20e1b544111c0255eb0fc04427aab7a5e3b877
Reviewed-on: https://go-review.googlesource.com/c/go/+/384158
Trust: Cherry Mui <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Currently, for stack traces (e.g. at panic or when runtime.Stack
is called), we print argument values from the stack. With register
ABI, we may never store the argument to stack therefore the
argument value on stack may be meaningless. This causes confusion.
This CL makes the compiler keep trace of which argument stack
slots are meaningful. If it is meaningful, it will be printed in
stack traces as before. If it may not be meaningful, it will be
printed as the stack value with a question mark ("?"). In general,
the value could be meaningful on some code paths but not others
depending on the execution, and the compiler couldn't know
statically, so we still print the stack value, instead of not
printing it at all. Also note that if the argument variable is
updated in the function body the printed value may be stale (like
before register ABI) but still considered meaningful.
Arguments passed on stack are always meaningful therefore always
printed without a question mark. Results are never printed, as
before.
(Due to a bug in the compiler we sometimes don't spill args into
their dedicated spill slots (as we should), causing it having
fewer meaningful values than it should be.)
This increases binary sizes a bit:
old new
hello 1129760 1142080 +1.09%
cmd/go 13932320 14088016 +1.12%
cmd/link 6267696 6329168 +0.98%
Fixes#45728.
Change-Id: I308a0402e5c5ab94ca0953f8bd85a56acd28f58c
Reviewed-on: https://go-review.googlesource.com/c/go/+/352057
Trust: Cherry Mui <cherryyz@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
runtime.no_pointers_stackmap is an odd beast.
It is defined in a Go file, populated by assembly,
used by the GC, and its address is magic used
by async pre-emption to ascertain whether a
routine was implemented in assembly.
A subsequent change will force all GC data into the go.func.* linker symbol.
runtime.no_pointers_stackmap is GC data, so it must go there.
Yet it also needs to go into rodata, for the runtime address trick.
This change eliminates it entirely.
Replace the runtime address check with the newly introduced asm funcflag.
Handle the assembly macro as magic, similarly to our handling of go_args_stackmap.
This allows the no_pointers_stackmap to be identical in all ways
to other gclocals stackmaps, including content-addressability.
Change-Id: Id2f20a262cfab0719beb88e6342984ec4b196268
Reviewed-on: https://go-review.googlesource.com/c/go/+/353672
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Currently, when the runtime printing a stack track (at panic, or
when runtime.Stack is called), it prints the function arguments
as words in memory. With a register-based calling convention,
the layout of argument area of the memory changes, so the
printing also needs to change. In particular, the memory order
and the syntax order of the arguments may differ. To address
that, this CL lets the compiler to emit some metadata about the
memory layout of the arguments, and the runtime will use this
information to print arguments in syntax order.
Previously we print the memory contents of the results along with
the arguments. The results are likely uninitialized when the
traceback is taken, so that information is rarely useful. Also,
with a register-based calling convention the results may not
have corresponding locations in memory. This CL changes it to not
print results.
Previously the runtime simply prints the memory contents as
pointer-sized words. With a register-based calling convention,
as the layout changes, arguments that were packed in one word
may no longer be in one word. Also, as the spill slots are not
always initialized, it is possible that some part of a word
contains useful informationwhile the rest contains garbage.
Instead of letting the runtime recreating the ABI0 layout and
print them as words, we now print each component separately.
Aggregate-typed argument/component is surrounded by "{}".
For example, for a function
F(int, [3]byte, byte) int
when called as F(1, [3]byte{2, 3, 4}, 5), it used to print
F(0x1, 0x5040302, 0xXXXXXXXX) // assuming little endian, 0xXXXXXXXX is uninitilized result
Now prints
F(0x1, {0x2, 0x3, 0x4}, 0x5).
Note: the liveness tracking of the spill splots has not been
implemented in this CL. Currently the runtime just assumes all
the slots are live and print them all.
Increase binary sizes by ~1.5%.
old new
hello (println) 1171328 1187712 (+1.4%)
hello (fmt) 1877024 1901600 (+1.3%)
cmd/compile 22326928 22662800 (+1.5%)
cmd/go 13505024 13726208 (+1.6%)
Updates #40724.
Change-Id: I351e0bf497f99bdbb3f91df2fb17e3c2c5c316dc
Reviewed-on: https://go-review.googlesource.com/c/go/+/304470
Trust: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Make them always true. Delete code that are only executed when
they are false.
Change-Id: I6194fa00de23486c2b0a0c9075fe3a09d9c52762
Reviewed-on: https://go-review.googlesource.com/c/go/+/264339
Trust: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Austin Clements <austin@google.com>
This drops package prefixes from the assembly code on 386 and arm. In
addition to just being nicer, this allows the assembler to
automatically pick up the argument stack map from the Go signatures of
these functions. This doesn't matter right now because these functions
never call back out to Go, but prepares us for the next CL.
Change-Id: I90fed7d4dd63ad49274529c62804211b6390e2e9
Reviewed-on: https://go-review.googlesource.com/c/go/+/262777
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Generate inline code at defer time to save the args of defer calls to unique
(autotmp) stack slots, and generate inline code at exit time to check which defer
calls were made and make the associated function/method/interface calls. We
remember that a particular defer statement was reached by storing in the deferBits
variable (always stored on the stack). At exit time, we check the bits of the
deferBits variable to determine which defer function calls to make (in reverse
order). These low-cost defers are only used for functions where no defers
appear in loops. In addition, we don't do these low-cost defers if there are too
many defer statements or too many exits in a function (to limit code increase).
When a function uses open-coded defers, we produce extra
FUNCDATA_OpenCodedDeferInfo information that specifies the number of defers, and
for each defer, the stack slots where the closure and associated args have been
stored. The funcdata also includes the location of the deferBits variable.
Therefore, for panics, we can use this funcdata to determine exactly which defers
are active, and call the appropriate functions/methods/closures with the correct
arguments for each active defer.
In order to unwind the stack correctly after a recover(), we need to add an extra
code segment to functions with open-coded defers that simply calls deferreturn()
and returns. This segment is not reachable by the normal function, but is returned
to by the runtime during recovery. We set the liveness information of this
deferreturn() to be the same as the liveness at the first function call during the
last defer exit code (so all return values and all stack slots needed by the defer
calls will be live).
I needed to increase the stackguard constant from 880 to 896, because of a small
amount of new code in deferreturn().
The -N flag disables open-coded defers. '-d defer' prints out the kind of defer
being used at each defer statement (heap-allocated, stack-allocated, or
open-coded).
Cost of defer statement [ go test -run NONE -bench BenchmarkDefer$ runtime ]
With normal (stack-allocated) defers only: 35.4 ns/op
With open-coded defers: 5.6 ns/op
Cost of function call alone (remove defer keyword): 4.4 ns/op
Text size increase (including funcdata) for go binary without/with open-coded defers: 0.09%
The average size increase (including funcdata) for only the functions that use
open-coded defers is 1.1%.
The cost of a panic followed by a recover got noticeably slower, since panic
processing now requires a scan of the stack for open-coded defer frames. This scan
is required, even if no frames are using open-coded defers:
Cost of panic and recover [ go test -run NONE -bench BenchmarkPanicRecover runtime ]
Without open-coded defers: 62.0 ns/op
With open-coded defers: 255 ns/op
A CGO Go-to-C-to-Go benchmark got noticeably faster because of open-coded defers:
CGO Go-to-C-to-Go benchmark [cd misc/cgo/test; go test -run NONE -bench BenchmarkCGoCallback ]
Without open-coded defers: 443 ns/op
With open-coded defers: 347 ns/op
Updates #14939 (defer performance)
Updates #34481 (design doc)
Change-Id: I63b1a60d1ebf28126f55ee9fd7ecffe9cb23d1ff
Reviewed-on: https://go-review.googlesource.com/c/go/+/202340
Reviewed-by: Austin Clements <austin@google.com>
Generate inline code at defer time to save the args of defer calls to unique
(autotmp) stack slots, and generate inline code at exit time to check which defer
calls were made and make the associated function/method/interface calls. We
remember that a particular defer statement was reached by storing in the deferBits
variable (always stored on the stack). At exit time, we check the bits of the
deferBits variable to determine which defer function calls to make (in reverse
order). These low-cost defers are only used for functions where no defers
appear in loops. In addition, we don't do these low-cost defers if there are too
many defer statements or too many exits in a function (to limit code increase).
When a function uses open-coded defers, we produce extra
FUNCDATA_OpenCodedDeferInfo information that specifies the number of defers, and
for each defer, the stack slots where the closure and associated args have been
stored. The funcdata also includes the location of the deferBits variable.
Therefore, for panics, we can use this funcdata to determine exactly which defers
are active, and call the appropriate functions/methods/closures with the correct
arguments for each active defer.
In order to unwind the stack correctly after a recover(), we need to add an extra
code segment to functions with open-coded defers that simply calls deferreturn()
and returns. This segment is not reachable by the normal function, but is returned
to by the runtime during recovery. We set the liveness information of this
deferreturn() to be the same as the liveness at the first function call during the
last defer exit code (so all return values and all stack slots needed by the defer
calls will be live).
I needed to increase the stackguard constant from 880 to 896, because of a small
amount of new code in deferreturn().
The -N flag disables open-coded defers. '-d defer' prints out the kind of defer
being used at each defer statement (heap-allocated, stack-allocated, or
open-coded).
Cost of defer statement [ go test -run NONE -bench BenchmarkDefer$ runtime ]
With normal (stack-allocated) defers only: 35.4 ns/op
With open-coded defers: 5.6 ns/op
Cost of function call alone (remove defer keyword): 4.4 ns/op
Text size increase (including funcdata) for go cmd without/with open-coded defers: 0.09%
The average size increase (including funcdata) for only the functions that use
open-coded defers is 1.1%.
The cost of a panic followed by a recover got noticeably slower, since panic
processing now requires a scan of the stack for open-coded defer frames. This scan
is required, even if no frames are using open-coded defers:
Cost of panic and recover [ go test -run NONE -bench BenchmarkPanicRecover runtime ]
Without open-coded defers: 62.0 ns/op
With open-coded defers: 255 ns/op
A CGO Go-to-C-to-Go benchmark got noticeably faster because of open-coded defers:
CGO Go-to-C-to-Go benchmark [cd misc/cgo/test; go test -run NONE -bench BenchmarkCGoCallback ]
Without open-coded defers: 443 ns/op
With open-coded defers: 347 ns/op
Updates #14939 (defer performance)
Updates #34481 (design doc)
Change-Id: I51a389860b9676cfa1b84722f5fb84d3c4ee9e28
Reviewed-on: https://go-review.googlesource.com/c/go/+/190098
Reviewed-by: Austin Clements <austin@google.com>
The pclntab encoding supports writing only some PCDATA and FUNCDATA values.
However, the encoding is dense: The max index in use determines the space used.
We should thus choose a numbering in which frequently used indices are smaller.
This change re-orders the PCDATA and FUNCDATA indices using that principle,
using a quick and dirty instrumentation to measure index frequency.
It shrinks binaries by about 0.5%.
Updates #6853
file before after Δ %
go 14745044 14671316 -73728 -0.500%
addr2line 4305128 4280552 -24576 -0.571%
api 6095800 6058936 -36864 -0.605%
asm 4930928 4906352 -24576 -0.498%
buildid 2881520 2861040 -20480 -0.711%
cgo 4896584 4867912 -28672 -0.586%
compile 25868408 25770104 -98304 -0.380%
cover 5319656 5286888 -32768 -0.616%
dist 3654528 3634048 -20480 -0.560%
doc 4719672 4691000 -28672 -0.607%
fix 3418312 3393736 -24576 -0.719%
link 6137952 6109280 -28672 -0.467%
nm 4250536 4225960 -24576 -0.578%
objdump 4665192 4636520 -28672 -0.615%
pack 2297488 2285200 -12288 -0.535%
pprof 14735332 14657508 -77824 -0.528%
test2json 2834952 2818568 -16384 -0.578%
trace 11679964 11618524 -61440 -0.526%
vet 8452696 8403544 -49152 -0.581%
Change-Id: I30665dce57ec7a52e7d3c6718560b3aa5b83dd0b
Reviewed-on: https://go-review.googlesource.com/c/go/+/171760
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Rework how the compiler+runtime handles stack-allocated variables
whose address is taken.
Direct references to such variables work as before. References through
pointers, however, use a new mechanism. The new mechanism is more
precise than the old "ambiguously live" mechanism. It computes liveness
at runtime based on the actual references among objects on the stack.
Each function records all of its address-taken objects in a FUNCDATA.
These are called "stack objects". The runtime then uses that
information while scanning a stack to find all of the stack objects on
a stack. It then does a mark phase on the stack objects, using all the
pointers found on the stack (and ancillary structures, like defer
records) as the root set. Only stack objects which are found to be
live during this mark phase will be scanned and thus retain any heap
objects they point to.
A subsequent CL will remove all the "ambiguously live" logic from
the compiler, so that the stack object tracing will be required.
For this CL, the stack tracing is all redundant with the current
ambiguously live logic.
Update #22350
Change-Id: Ide19f1f71a5b6ec8c4d54f8f66f0e9a98344772f
Reviewed-on: https://go-review.googlesource.com/c/134155
Reviewed-by: Austin Clements <austin@google.com>
In order to generate accurate tracebacks, the runtime needs to know the
inlined call stack for a given PC. This creates two tables per function
for this purpose. The first table is the inlining tree (stored in the
function's funcdata), which has a node containing the file, line, and
function name for every inlined call. The second table is a PC-value
table that maps each PC to a node in the inlining tree (or -1 if the PC
is not the result of inlining).
To give the appearance that inlining hasn't happened, the runtime also
needs the original source position information of inlined AST nodes.
Previously the compiler plastered over the line numbers of inlined AST
nodes with the line number of the call. This meant that the PC-line
table mapped each PC to line number of the outermost call in its inlined
call stack, with no way to access the innermost line number.
Now the compiler retains line numbers of inlined AST nodes and writes
the innermost source position information to the PC-line and PC-file
tables. Some tools and tests expect to see outermost line numbers, so we
provide the OutermostLine function for displaying line info.
To keep track of the inlined call stack for an AST node, we extend the
src.PosBase type with an index into a global inlining tree. Every time
the compiler inlines a call, it creates a node in the global inlining
tree for the call, and writes its index to the PosBase of every inlined
AST node. The parent of this node is the inlining tree index of the
call. -1 signifies no parent.
For each function, the compiler creates a local inlining tree and a
PC-value table mapping each PC to an index in the local tree. These are
written to an object file, which is read by the linker. The linker
re-encodes these tables compactly by deduplicating function names and
file names.
This change increases the size of binaries by 4-5%. For example, this is
how the go1 benchmark binary is impacted by this change:
section old bytes new bytes delta
.text 3.49M ± 0% 3.49M ± 0% +0.06%
.rodata 1.12M ± 0% 1.21M ± 0% +8.21%
.gopclntab 1.50M ± 0% 1.68M ± 0% +11.89%
.debug_line 338k ± 0% 435k ± 0% +28.78%
Total 9.21M ± 0% 9.58M ± 0% +4.01%
Updates #19348.
Change-Id: Ic4f180c3b516018138236b0c35e0218270d957d3
Reviewed-on: https://go-review.googlesource.com/37231
Run-TryBot: David Lazar <lazard@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
The comments in cmd/internal/obj/funcdata.go are identical to the
comments in runtime/funcdata.h, but the majority of the definitions
they refer to don't apply to Go sources and have been stripped out of
funcdata.go.
Remove these stale comments from funcdata.go and clean up the
references to other copies of the PCDATA and FUNCDATA indexes.
Change-Id: I5d6e49a6e586cc9aecd7c3ce1567679f2a605884
Reviewed-on: https://go-review.googlesource.com/37330
Reviewed-by: Keith Randall <khr@golang.org>
This is a subset of https://golang.org/cl/20022 with only the copyright
header lines, so the next CL will be smaller and more reviewable.
Go policy has been single space after periods in comments for some time.
The copyright header template at:
https://golang.org/doc/contribute.html#copyright
also uses a single space.
Make them all consistent.
Change-Id: Icc26c6b8495c3820da6b171ca96a74701b4a01b0
Reviewed-on: https://go-review.googlesource.com/20111
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
The conversion was done with an automated tool and then
modified only as necessary to make it compile and run.
[This CL is part of the removal of C code from package runtime.
See golang.org/s/dev.cc for an overview.]
LGTM=r
R=r, austin
CC=dvyukov, golang-codereviews, iant, khr
https://golang.org/cl/167550043
The argsize PCDATA was specifying the number of
bytes passed to a function call, so that if the function
did not specify its argument count, the garbage collector
could use the call site information to scan those bytes
conservatively. We don't do that anymore, so stop
generating the information.
LGTM=khr
R=khr
CC=golang-codereviews
https://golang.org/cl/139530043
The goal here is to allow assembly functions to appear in the middle
of a Go stack (having called other code) and still record enough information
about their pointers so that stack copying and garbage collection can handle
them precisely. Today, these frames are handled only conservatively.
If you write
func myfunc(x *float64) (y *int)
(with no body, an 'extern' declaration), then the Go compiler now emits
a liveness bitmap for use from the assembly definition of myfunc.
The bitmap symbol is myfunc.args_stackmap and it contains two bitmaps.
The first bitmap, in effect at function entry, marks all inputs as live.
The second bitmap, not in effect at function entry, marks the outputs
live as well.
In funcdata.h, define new assembly macros:
GO_ARGS opts in to using the Go compiler-generated liveness bitmap
for the current function.
GO_RESULTS_INITIALIZED indicates that the results have been initialized
and need to be kept live for the remainder of the function; it causes a
switch to the second generated bitmap for the assembly code that follows.
NO_LOCAL_POINTERS indicates that there are no pointers in the
local variables being stored in the function's stack frame.
LGTM=khr
R=khr
CC=golang-codereviews
https://golang.org/cl/137520043
Austin Clements
Cherry Mui
Josh Bleecher Snyder
Dan Scales
Bryan C. Mills
Keith Randall
Xia Bin
David Lazar
Richard Miller
Brad Fitzpatrick
Michael Hudson-Doyle
Russ Cox