[browser][CoreCLR] Trimming feature System.Diagnostics.StackTrace.IsLineNumberSupported #123429

pavelsavara · 2026-01-21T11:54:38Z

Added[FeatureSwitchDefinition("System.Diagnostics.StackTrace.IsLineNumberSupported")]
triggered by <StackTraceLineNumberSupport>false</StackTraceLineNumberSupport>
wich is set by default in WASM for Release

saves 214KB of uncompressed IL from hello world

Copilot

Pull request overview

This PR optimizes browser/WASM builds by disabling stack trace file information (filename, line number, column number) collection for the TARGET_BROWSER platform. This saves approximately 214KB of uncompressed IL from hello world applications.

Changes:

Guard file info population code in StackFrameHelper.InitializeSourceInfo with #if !TARGET_BROWSER
Guard static reentrancy tracking fields used only for file info processing
Guard file info field assignments in StackFrame constructors
Add CA1822 pragma suppression for InitializeSourceInfo (needed because the method doesn't use instance state on browser)

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
`src/coreclr/System.Private.CoreLib/src/System/Diagnostics/StackFrameHelper.cs`	Guards file info processing logic and reentrancy tracking with `#if !TARGET_BROWSER`, adds CA1822 suppression
`src/coreclr/System.Private.CoreLib/src/System/Diagnostics/StackFrame.CoreCLR.cs`	Guards file info field assignments in constructor and `BuildStackFrame` method with `#if !TARGET_BROWSER`

pavelsavara · 2026-01-21T14:20:21Z

We can eventually hide this behind some feature flag. So that in debug build, we would have full fidelity stack trace with line numbers.

There is System.Diagnostics.StackTrace.IsSupported but it does something else related to DiagnosticMethodInfo

Could the same flag be used here ? @jkotas

dotnet-policy-service · 2026-01-21T14:24:42Z

Tagging subscribers to 'size-reduction': @eerhardt, @SamMonoRT, @marek-safar
See info in area-owners.md if you want to be subscribed.

src/coreclr/System.Private.CoreLib/src/System/Diagnostics/StackFrame.CoreCLR.cs

jkotas · 2026-01-21T16:04:49Z

Is the stack trace line number support unconditionally disabled in Mono Browser today? Trying to understand whether we need extra work to get CoreCLR to parity with Mono Browser.

Could the same flag be used here?

The existing msbuild property that does the same thing is StackTraceLineNumberSupport. It is NAOT-specific and it was introduced just recently. We would want to use the same one here.

steveisok · 2026-01-21T16:59:18Z

Is the stack trace line number support unconditionally disabled in Mono Browser today? Trying to understand whether we need extra work to get CoreCLR to parity with Mono Browser.

Not 100% sure, but I don't think we do anything special. If

runtime/src/mono/mono/metadata/mono-debug.c

Line 799 in 46c884e

    
           mono_debug_lookup_source_location (MonoMethod *method, guint32 address, MonoDomain *domain)

returns NULL, it won't display file info.

The existing msbuild property that does the same thing is StackTraceLineNumberSupport. It is NAOT-specific and it was introduced just recently. We would want to use the same one here.

I was wondering the same thing. And perhaps apply it in https://github.com/dotnet/runtime/blob/5dd95537d5faa20e8baed719e9f5f18d5f29494c/src/libraries/System.Private.CoreLib/src/System/Diagnostics/StackTrace.cs instead of the CoreCLR specific file.

pavelsavara · 2026-01-21T17:08:40Z

Is the stack trace line number support unconditionally disabled in Mono Browser today?

Mono doesn't use StackFrameHelper at all.
It doesn't print line numbers on mono/wasm either (in release/publish mode)
I just tested it.

Trying to understand whether we need extra work to get CoreCLR to parity with Mono Browser.

214KB is 4% of mono wasm hello world download size

StackTraceLineNumberSupport

Thanks!

steveisok · 2026-01-21T17:14:01Z

Mono doesn't use StackFrameHelper at all. It doesn't print line numbers on mono/wasm either (in release/publish mode) I just tested it.

I think from the BCL perspective it's still passing that it wants line numbers into an icall. I suspect we aren't getting them as a byproduct as opposed to doing something explicit for wasm.

pavelsavara · 2026-01-21T17:17:53Z

runtime/src/mono/mono/mini/mini-exceptions.c

Line 1456 in ebae784

mono_get_frame_info (gint32 skip,

runtime/src/mono/mono/metadata/mono-debug.c

Lines 789 to 800 in ebae784

    
           /** 
        
            * mono_debug_lookup_source_location: 
        
            * \param address Native offset within the \p method's machine code. 
        
            * Lookup the source code corresponding to the machine instruction located at 
        
            * native offset \p address within \p method. 
        
            * The returned \c MonoDebugSourceLocation contains both file / line number 
        
            * information and the corresponding IL offset.  It must be freed by 
        
            * \c mono_debug_free_source_location. 
        
            */ 
        
           MonoDebugSourceLocation * 
        
           mono_debug_lookup_source_location (MonoMethod *method, guint32 address, MonoDomain *domain) 
        
           {

pavelsavara · 2026-01-21T17:29:37Z

It seems to me that Mono functionality depends on debugger native module being linked in and also on PDB information being available.

jkotas · 2026-01-21T17:37:14Z

It doesn't print line numbers on mono/wasm either (in release/publish mode)

What does it do in debug builds?

pavelsavara · 2026-01-21T17:45:53Z

It doesn't print line numbers on mono/wasm either (in release/publish mode)

What does it do in debug builds?

Test exception for stack trace
   at StopwatchSample.Baz() in D:\samples\debug-stack-trace\Program.cs:line 52
   at StopwatchSample.Bar() in D:\samples\debug-stack-trace\Program.cs:line 48
   at StopwatchSample.Foo() in D:\samples\debug-stack-trace\Program.cs:line 44
   at StopwatchSample.Toggle() in D:\samples\debug-stack-trace\Program.cs:line 30
   at StopwatchSample.<__Wrapper_Toggle_18729595>g____Stub|10_0(JSMarshalerArgument* ____arg_exception_native__param, JSMarshalerArgument* __invokeRetValUnmanaged__param) in D:\samples\debug-stack-trace\obj\Debug\net10.0\Microsoft.Interop.JavaScript.JSImportGenerator\Microsoft.Interop.JavaScript.JSExportGenerator\JSExports.g.cs:line 42
Error: Test exception for stack trace
    at un (https://localhost:7005/_framework/dotnet.runtime.0j6ezsi0n0.js:3:27547)
    at kn (https://localhost:7005/_framework/dotnet.runtime.0j6ezsi0n0.js:3:29564)
    at Object.<anonymous> (https://localhost:7005/_framework/dotnet.runtime.0j6ezsi0n0.js:3:39269)
    at HTMLButtonElement.<anonymous> (https://localhost:7005/main.ofkecrt505.js:26:47)

jkotas · 2026-01-21T17:48:01Z

So this PR will regress debug builds and improve size of release builds. I am not sure whether it is an improvement

pavelsavara · 2026-01-21T17:50:28Z

So this PR will regress debug builds and improve size of release builds. I am not sure whether it is an improvement

No this PR (in current shape) was conversation opener.

If we introduce that StackTraceLineNumberSupport as feature flag for that is false in browser release by default, we would be golden 🚀

…umberSupport

pavelsavara · 2026-01-27T12:48:04Z

With [FeatureSwitchDefinition("System.Diagnostics.StackTrace.IsLineNumberSupported")] triggered by <StackTraceLineNumberSupport>false</StackTraceLineNumberSupport> by default in Release

Trimmed

Size is the same as above.

src/libraries/System.Private.CoreLib/src/System/Diagnostics/StackTrace.cs

...nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets

- trimming test

pavelsavara · 2026-01-29T08:23:12Z

pavelsavara · 2026-01-29T08:23:23Z

/ba-g CI timeouts

no file info

3be427c

pavelsavara added this to the 11.0.0 milestone Jan 21, 2026

pavelsavara requested review from jkotas and radekdoulik January 21, 2026 11:54

pavelsavara self-assigned this Jan 21, 2026

pavelsavara added arch-wasm WebAssembly architecture area-System.Diagnostics labels Jan 21, 2026

Copilot AI review requested due to automatic review settings January 21, 2026 11:54

pavelsavara added the os-browser Browser variant of arch-wasm label Jan 21, 2026

Copilot started reviewing on behalf of pavelsavara January 21, 2026 11:55 View session

Copilot AI reviewed Jan 21, 2026

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Merge branch 'main' into browser_simple_stack_trace

5dd9553

pavelsavara added the size-reduction Issues impacting final app size primary for size sensitive workloads label Jan 21, 2026

jkotas reviewed Jan 21, 2026

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src/coreclr/System.Private.CoreLib/src/System/Diagnostics/StackFrame.CoreCLR.cs Outdated Show resolved Hide resolved

pavelsavara marked this pull request as draft January 21, 2026 17:59

pavelsavara added 2 commits January 27, 2026 12:10

Merge branch 'main' into browser_simple_stack_trace

320fc1f

System.Diagnostics.StackTrace.IsLineNumberSupported + StackTraceLineN…

d12ad25

…umberSupport

pavelsavara added 2 commits January 27, 2026 18:38

Merge branch 'main' into browser_simple_stack_trace

03ae566

Merge branch 'main' into browser_simple_stack_trace

8b7a078

pavelsavara marked this pull request as ready for review January 28, 2026 11:06

pavelsavara requested review from akoeplinger and lewing as code owners January 28, 2026 11:06

pavelsavara requested a review from jkotas January 28, 2026 18:09

jkotas reviewed Jan 28, 2026

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src/libraries/System.Private.CoreLib/src/System/Diagnostics/StackTrace.cs Outdated Show resolved Hide resolved

jkotas reviewed Jan 28, 2026

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...nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets Outdated Show resolved Hide resolved

jkotas approved these changes Jan 28, 2026

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pavelsavara added 2 commits January 28, 2026 21:49

feedback

b4203c9

- use DebugSymbols to trigger StackTraceLineNumberSupport

524859f

- trimming test

build-analysis bot mentioned this pull request Jan 29, 2026

[Wasm] The request was canceled due to the configured HttpClient.Timeout of 100 seconds elapsing #123572

Open

pavelsavara merged commit 62006a2 into dotnet:main Jan 29, 2026
154 of 159 checks passed

pavelsavara deleted the browser_simple_stack_trace branch January 29, 2026 08:24

pavelsavara changed the title ~~[browser][CoreCLR] remove file info from stack traces~~ [browser][CoreCLR] Trimming feature System.Diagnostics.StackTrace.IsLineNumberSupported Jan 29, 2026

dotnet-maestro bot mentioned this pull request Jan 30, 2026

[main] Source code updates from dotnet/runtime dotnet/dotnet#4544

Merged

[browser][CoreCLR] Trimming feature System.Diagnostics.StackTrace.IsLineNumberSupported #123429

[browser][CoreCLR] Trimming feature System.Diagnostics.StackTrace.IsLineNumberSupported #123429

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