Re: [go-nuts] Getting a function's linked address?
For the record, I could do what I needed using the `//go:linkname` directive. My instrumentation tool injects statements that need features from another package that I cannot import. So I forward declare functions using a given link name that is implemented in another package - similarly to what can be found in the stdlib. This way, the forward declarations get resolved at link time - similarly to what you can do with `extern` with GCC. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/e871a4f3-b9e4-4714-aec1-ca0fa95232f4%40googlegroups.com.
[go-nuts] Re: How to print an AST without formatting?
I saw `go tool cover` does it, but I don't see anything else but a simple call to printer.Fprint(w, f.fset, f.astFile) at https://github.com/golang/tools/blob/master/cmd/cover/cover.go#L384 -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/362b2c19-8dfa-455d-bf74-04d9c1ff589a%40googlegroups.com.
[go-nuts] How to print an AST without formatting?
Hello, I am looking for a way to keep to original token positioning but I cannot find how to avoid it when using `go/printer` or `go/format`. Basically, how to make this example print the same string that was parsed: https://play.golang.org/p/dI7WcevQJAZ Thanks for your help! Julio -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/fbf8e5b6-f237-470c-9267-246132a2e0bc%40googlegroups.com.
[go-nuts] Re: Enforcing a type name rather than a variable name
By the way, here is the function having this in package `net`: https://golang.org/src/net/lookup.go#L81 -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/3365c11e-918e-4bd7-989b-46868148b1ec%40googlegroups.com.
[go-nuts] Enforcing a type name rather than a variable name
Hello, Is there any way to avoid the compilation error "*error is not a type" of this example https://play.golang.org/p/gWNStGSCfTm ? I understand the variable named `error` hides the type named `error` but is there some other syntax to specify the error type? I am facing this issue while writing an instrumentation tool: some functions the tool instruments have such signatures, while the tool add Go code referencing the type name, not the variable name. Thanks for your help -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/8612f73c-bfb4-4bce-a5d3-3567ee2cbd9a%40googlegroups.com.
Re: [go-nuts] Assigning a value to a function pointer
> > But I cannot find any way of assigning a value to the function pointer > `f` even using the `unsafe` package. > > https://play.golang.org/p/qP5kuSCW6dO > Thanks, unfortunately the asm shows that what gets into `f` is the stack address of `f0` and not the address of the function: LEAQ"".foo·f(SB), DX MOVQDX, "".f0(SP) // f0 = foo MOVQ"".f0(SP), DX // f = MOVQ(DX), AX // *f I'd love to find how to directly use the address without any local variable :-) -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/3ac144bc-7d4c-4400-945a-33d2163780cd%40googlegroups.com.
[go-nuts] Assigning a value to a function pointer
Hello,
The following Go program has a valid syntax:
https://play.golang.org/p/V7bIGnTu1fb
But I cannot find any way of assigning a value to the function pointer `f`
even using the `unsafe` package.
My main reason for willing this is to be able to:
- atomically load a dynamic address.
- avoid using instead `*interface{}` (that I can atomically load +
type-assert + call).
Thanks for your help,
Julio
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Re: [go-nuts] Getting a function's linked address?
> > You can create a lookup table at run time. What would change if you > could do it at link time? Can you show us the code you want to write? > This is actually linked to my remark on build-time source instrumentation on https://github.com/golang/go/issues/35204 : I insert hooks into functions and then use a lookup table to find them at run time. Currently, they are created using a function which adds the newly created pointer into a global map, thus done at "Go init time". But if we say that I shouldn't add new dependencies when from a -toolexec tool, I need to create this same lookup table differently. TBH, I just would like to know if getting a symbol address at link time is possible. Because I actually found today a workaround to be able to add new dependencies my -toolexec tool. But I may need to do this later on. The other idea I had in mind was using the gosymtab to find function adresses but it looks like this section is not always present and I am not sure how long it will be supported. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/e3c50e8b-f1d0-47a2-ae03-53b2ae4f00db%40googlegroups.com.
Re: [go-nuts] Getting a function's linked address?
I was meaning an equivalent to declaring an extern function using the same name as the symbol we want. The function address will be the linked symbol address. I indeed use the reflect package today, but this happen at run time while I would like to get those values at link time. I'd like to create a lookup table to function addresses. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/3c4465bd-aeac-4188-98d2-810e19541c5b%40googlegroups.com.
[go-nuts] Getting a function's linked address?
Hello, I am wondering if it is possible to get the address of a function but at link-time. Kind of the equivalent to the C keyword `extern`. Maybe using the link name directive? But it is not super clear to me. I would like to get them instead at link time instead of using the gosymtab. Thank you -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/7649f370-2720-4630-b441-e08b7709f960%40googlegroups.com.
[go-nuts] Distributing Go bindings: Go plugin vs Go archive vs Go shared package
Hello! I am trying to find out the best way to distribute Go bindings to a C library. I would like to avoid asking my users to install their target gcc because of cgo. So my idea is to avoid cgo by avoiding having my user compiling the bindings, by therefore distributing an already compiled package for every target GOOS and GOARCH. Some discussions on Go plugins I found are about this precise case but it is not supported on Windows so far. But I really don't get why isn't it possible to simply use the archive build mode `-buildmode archive` on the bindings, then include the resulting Go package archive in the repo, and simply use some go CLI option in order to use the correct archive for the target GOOS/GOARCH? I couldn't find out how to pass such option to the go compiler so far, so I was hoping for some help. Thanks for your help, Julio -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/601106da-f825-47cf-b0b1-56a2e026d7e4%40googlegroups.com.
[go-nuts] How to safely convert a pointer to *unsafe.Pointer
Hello, I would like to make sure that the following line of Go is a defined behavior: addr := (*unsafe.Pointer)((unsafe.Pointer)()) I use it to perform atomic loads and stores to addr such as in this simple example: https://play.golang.org/p/DpDrRvTYMG8 It allows me not to use atomic.Value which performs two atomic operations and possible disable preemption ( https://golang.org/src/sync/atomic/value.go?s=1233:1269#L35). Thanks for your help, Julio -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/3bc36e02-c821-4241-b929-c9c5abd5b4b7%40googlegroups.com.
Re: [go-nuts] [RFC] Dynamically instrumentation Go binaries
On Thu, Nov 15, 2018 at 9:57 PM Tristan Colgate wrote: > Maybe you mean something like support for linux uprobes? > There is some discussion here: > https://github.com/golang/go/issues/22008 > Google for "golang uprobes" picks up a couple of other links: > > http://www.brendangregg.com/blog/2017-01-31/golang-bcc-bpf-function-tracing.html > > https://kinvolk.io/blog/2017/09/an-update-on-gobpf---elf-loading-uprobes-more-program-types/ > Ran a small benchmark using uprobes and there's no overhead for an io-bound function, for a cpu-bound function, it is twice slower. So it may be a very good solution for a first linux-only version, as I don't need return probes (uretprobes seem to be a problem with Go's dynamic stack management). -- Julio Guerra -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [go-nuts] [RFC] Dynamically instrumentation Go binaries
On Thu, Nov 15, 2018 at 7:55 PM Michael Jones wrote: > You could study Rob Pike’s coverage/profiling tool to see how he adds and > exploits basic block counting. Good work as always. > Good idea, thanks. I had a look at the implementation of it, and at the way it is integrated into the go toolchain. Unfortunately, it doesn't seem possible to include extra compilation stages in the toolchain. I was hoping for a way to insert an extra step to be able to modify the AST to insert tracepoints. So, for example, coverage is built inside `go test` by directly calling `go cover`, and it doesn't use any plugin interface :( -- Julio Guerra -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [go-nuts] Re: [RFC] Dynamically instrumentation Go binaries
On Fri, Nov 16, 2018 at 12:06 AM Damian Gryski wrote: > One approach would be to augment the compiler to instrument the binary > with the techniques outlined in: > > XRay: A Function Call Tracing System > https://ai.google/research/pubs/pub45287 > > Yes, this is very likely the best option for performance and to avoid code relocation at run time... Unfortunately, the go toolchain currently doesn't have any "plugin" interface to add extra compilation stages. -- Julio Guerra -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[go-nuts] [RFC] Dynamically instrumentation Go binaries
Hi, I am working on dynamic instrumentation of Go programs at run time, possibly without static source-code instrumentation. As I would like a solution as close to Go and standard as possible, I was first thinking of using `go generate` to generate a file adding things `reflect` doesn't provide such as the list of packages, functions, global variables... That way, I should be able to use `reflect` to modify any dynamic calls by modifying the method tables of their underlying type representations. But regarding statically linked calls, the less intrusive technique I found are uprobes, which is linux-specific. And at the opposite, there are user-space binary code instrumentation libraries such as dyninst that modify the code at run time... So I am wondering if anyone here has any thoughts on this subject, that doesn't seem to be solved for Go programs. Thanks! Julio -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [go-nuts] Is it safe to invoke len(channel) on multi-gorountine
I almost got into the trap with this, trying to prioritize selected channel... https://play.golang.org/p/VOrPwx7HC_ -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
