runtime: support SEH stack unwinding on Windows #57302
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I don't see any API changes here, so I don't think this needs to go through the proposal process. I think the runtime team and the Windows team can make a decision here. Thanks. |
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CC @golang/runtime @golang/windows |
Makes sense. Side note: I open to lead this implementation as part of my job at Microsoft, I don't expect nor ask the Go compiler/runtime team to jump into this by their own. |
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I think we should accept these changes. @qmuntal it would help if you create new issues demonstrating problems you intend to fix. You mention #49471 , but I suspect there are others. Broken WinDbg or Windows Performance Analyzer or other tools are OK for these issues. It would help Go team to make this decision once they see what they are getting for adding new code. Thank you. Alex |
That's a very good advice. Will do that! |
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Change https://go.dev/cl/459395 mentions this issue: |
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Change https://go.dev/cl/461736 mentions this issue: |
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Change https://go.dev/cl/461737 mentions this issue: |
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Change https://go.dev/cl/461738 mentions this issue: |
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Change https://go.dev/cl/461749 mentions this issue: |
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Change https://go.dev/cl/457455 mentions this issue: |
This CL updates the linker to support IMAGE_REL_[I386|AMD64|ARM|ARM64]_ADDR32NB relocations via the new R_PEIMAGEOFF relocation type. This relocation type references symbols using RVAs instead of VA, so it can use 4-byte offsets to reference symbols that would normally require 8-byte offsets. This new relocation is still not used, but will be useful when generating Structured Exception Handling (SEH) metadata, which needs to reference functions only using 4-byte addresses, thus using RVAs instead of VA is of great help. Updates #57302 Change-Id: I28d73e97d5cb78a3bc7194dc7d2fcb4a03f9f4d0 Reviewed-on: https://go-review.googlesource.com/c/go/+/461737 Reviewed-by: Ian Lance Taylor <iant@google.com> Reviewed-by: Cherry Mui <cherryyz@google.com> Run-TryBot: Quim Muntal <quimmuntal@gmail.com> Reviewed-by: Davis Goodin <dagood@microsoft.com> TryBot-Result: Gopher Robot <gobot@golang.org>
This CL updates the Go compiler so it generate SEH unwind info [1] as a function auxiliary symbol when building for windows/amd64. A follow up CL will teach the Go linker how to assemble these codes into the PE .xdata section. Updates #57302 [1] https://learn.microsoft.com/en-us/cpp/build/exception-handling-x64#struct-unwind_info Change-Id: I40ae0437bfee326c1a67c2b5e1496f0bf3ecea17 Reviewed-on: https://go-review.googlesource.com/c/go/+/461749 Reviewed-by: Davis Goodin <dagood@microsoft.com> Reviewed-by: Michael Knyszek <mknyszek@google.com> TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Than McIntosh <thanm@google.com> Run-TryBot: Quim Muntal <quimmuntal@gmail.com>
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1 month till freeze, but just 2 CLs for review remaining. Could you take a look to CL 461738 and CL 457455 @cherrymui and @thanm? Thanks! |
This CL adds a .pdata section to the PE file generated by the Go linker. The .pdata section is a standard section [1] that contains an array of function table entries that are used for stack unwinding. The table entries layout is taken from [2]. This CL just generates the table entries without any unwinding information, which is enough to start doing some E2E tests between the Go linker and the Win32 APIs. The goal of the .pdata table is to allow Windows retrieve unwind information for a function at a given PC. It does so by doing a binary search on the table, looking for an entry that meets BeginAddress >= PC < EndAddress. Each table entry takes 12 bytes and only non-leaf functions with frame pointer needs an entry on the .pdata table. The result is that PE binaries will be ~0.7% bigger due to the unwind information, a reasonable amount considering the benefits in debuggability. Updates #57302 [1] https://learn.microsoft.com/en-us/windows/win32/debug/pe-format#the-pdata-section [2] https://learn.microsoft.com/en-us/cpp/build/exception-handling-x64#struct-runtime_function Change-Id: If675d10c64452946dbab76709da20569651e3e9f Reviewed-on: https://go-review.googlesource.com/c/go/+/461738 TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Alex Brainman <alex.brainman@gmail.com> Reviewed-by: Than McIntosh <thanm@google.com> Run-TryBot: Quim Muntal <quimmuntal@gmail.com> Reviewed-by: Cherry Mui <cherryyz@google.com>
This CL adds a .xdata section to the PE file generated by the Go linker. It is also the first CL of the SEH chain that adds effective support for unwinding the Go stack, as demonstrated by the newly added tests. The .xdata section is a standard PE section that contains an array of unwind data info structures. This structures are used to record the effects a function has on the stack pointer, and where the nonvolatile registers are saved on the stack [1]. Note that this CL still does not support unwinding the cgo stack. Updates #57302 [1] https://learn.microsoft.com/en-us/cpp/build/exception-handling-x64#struct-unwind_info Change-Id: I6f305a51ed130b758ff9ca7b90c091e50a109a6f Reviewed-on: https://go-review.googlesource.com/c/go/+/457455 Reviewed-by: Cherry Mui <cherryyz@google.com> Reviewed-by: Davis Goodin <dagood@microsoft.com> Run-TryBot: Quim Muntal <quimmuntal@gmail.com> TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Than McIntosh <thanm@google.com>
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Change https://go.dev/cl/499515 mentions this issue: |
While here, I've removed the CL 472195 TODO, which I marked as RELNOTE=yes by mistake. For #57441 For #57302 Change-Id: I7563140bf307f8d732f0154d02b8fa0735527323 Reviewed-on: https://go-review.googlesource.com/c/go/+/499515 Reviewed-by: Ian Lance Taylor <iant@google.com> TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Michael Knyszek <mknyszek@google.com> Run-TryBot: Quim Muntal <quimmuntal@gmail.com>
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Thanks for all of this work @qmuntal ! Is there more to be done here, or can we close this issue at this point? |
I haven't close it yet because SEH is still not implemented on windows/arm64, but I'm fine closing this bigger issue and open a more specific follow up issue. What do you recommend? |
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@qmuntal I think we just kick it to the next milestone and update the original post; possibly also the title. |
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While investigating #62887 I found out that, on windows/amd64 using internal linking, the Go linker doesn't merge .pdata/.xdata sections from host object files generated by the C compiler. This means that the stack can't be unwind in C -> Go transitions. I'm preparing a fix for that. |
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Change https://go.dev/cl/534555 mentions this issue: |
…files The Go linker doesn't currently merge .pdata/.xdata sections from the host object files generated by the C compiler when using internal linking. This means that the stack can't be unwind in C -> Go. This CL fixes that and adds a test to ensure that the stack can be unwind in C -> Go and Go -> C transitions, which was not well tested. Updates #57302 Change-Id: Ie86a5e6e30b80978277e66ccc2c48550e51263c8 Reviewed-on: https://go-review.googlesource.com/c/go/+/534555 Reviewed-by: Heschi Kreinick <heschi@google.com> Reviewed-by: Cherry Mui <cherryyz@google.com> LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Than McIntosh <thanm@google.com>
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Hi @qmuntal , what is the status for this now? Is there more to do? Should we bump to Go 1.23? Thanks. |
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@qmuntal Also, is there anything that worth mentioning in the Go 1.22 release notes? Thanks. |
windows/arm64 work still missing. I'll probably won't have bandwidth to implement it for Go 1.23, so we can move it to the backlog.
Yep, good point. CL 534555 and CL 525475, which should have linked this issue, deserve to be part of the release notes, as they can sublety alter program behavior (in a good way). I'll submit the corresponding release notes CL. |
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Friendly ping, just checking to see if you have had a chance to look into writing a release notes CL. Thanks. |
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Change https://go.dev/cl/548575 mentions this issue: |
For #57302. For #61422. Change-Id: Iee4e6600bf473eb982d0cb7330f7b2c1b48b9e13 Reviewed-on: https://go-review.googlesource.com/c/go/+/548575 Reviewed-by: Cherry Mui <cherryyz@google.com> LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Than McIntosh <thanm@google.com> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
For golang#57302. For golang#61422. Change-Id: Iee4e6600bf473eb982d0cb7330f7b2c1b48b9e13 Reviewed-on: https://go-review.googlesource.com/c/go/+/548575 Reviewed-by: Cherry Mui <cherryyz@google.com> LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Than McIntosh <thanm@google.com> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Status update: SEH stack unwinding has been implemented in go1.20 for windows/amd64. Still missing windows/arm64.
Background
Go binaries can't be reliably debugged or profiled with native Windows tools, such as WinDbg or the Windows Performance Analyzer, because Go does not generate PE files which contains the necessary static data that Win32 functions like RtlVirtualUnwind and StackWalk use to unwind the stack.
Delve and
go tool pprofare great tools for developing on Windows, but production environments that run on Windows tend to rely on language-agnostic tools provided by Microsoft for profiling and troubleshooting. Stack unwinding is such a fundamental thing for all these tools, and Go not supporting it is a major pain point in the Windows ecosystem, at least when running production workloads.Proposal
The Go compiler and linker should emit the necessary SEH static data for each Go function to reliably unwind and walk the stack using the Windows stack unwind conventions for each architecture:
This new information will slightly increase the size of the final binary, around 12 bytes per non-leaf functions.
Stack unwinding overview
Note: each architecture has slightly different design, the following explanation is based on x64.
Stack unwinding normally take place in these three cases:
RtlVirtualUnwind unwinds exactly one frame from the stack and has two important parameters:
ControlPCandFunctionEntry. The former is the PC from where to start the unwinding, and the later is the frame information of the current function. This frame information is what comes from the static data in the PE files, more specifically from the.pdataand.xdatasections. It contains the following bits: function length, prolog length, frame pointer location (if used), where does the stack grow to accommodate local variable, how to restore non-volatile registers, and the exception handler address (if any). RtlVirtualUnwind will use this information to restore the context of the calling function without physically walking the stack. If this information is not present (current situation in Go binaries), it will naively take the return address from the last 4/8 bytes of the stack, which really only works for leaf functions, and for non-leaf functions it means that the return address points to whatever value the last local variable happens to contain.There is one important outcome of this explanation: tools using RtlVirtualUnwind will unwind Go binaries even if no unwind information is present in the PE (current situation), this process will never work correctly unless unwinding a leaf function. So, whatever we do, even if not perfect, will be an improvement over the current situation.
Implementation
I would rather keep the implementation details out of this discussion, it is doable and there any many ways to implement it, from naively generating the info in the linker (see prototype CL 457455) to a detailed stack frame representation generated by the compiler and the linker.
If this proposal is accepted, I would suggest implementing it incrementally, starting by just enabling stack walking and finishing with an accurate representation of the non-volatile registries at every frame of the call stack.
@golang/windows @golang/compiler
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