[.NET 8] Some Symbol Entries in perf-%pid.map Are Truncated #102938

Description

There is a regression in .NET 8 where symbols written to perf-%pid.map can be truncated. This means that profiling tools can display the wrong symbols after a profile has been captured on Linux.

Reproduction Steps

1. Build the following application against .NET 8 on Linux:

using System;

public static class Program
{
    public static void Main(string[] args)
    {
        while(true)
        {
            Console.WriteLine();
        }
    }
}

2. Run export COMPlus_PerfMapEnabled=1 to enable generation of perf-%pid.map files.
3. Clear all perf-%pid.map files from /tmp.
4. Run the application built in step 1 and then kill it via CTRL+C.
5. Open /tmp/perf-%pid.map for the application. There is likely only one because we cleared out all the previous files.
6. Search for ConsolePal::Writ(.

Expected behavior

An entry for System.ConsolePal::Write should exist. Here's an example correct entry:

0x7fb99c69d090 22a void [System.Console] System.ConsolePal::Write(class [System.Runtime]Microsoft.Win32.SafeHandles.SafeFileHandle,valuetype [System.Runtime]System.ReadOnlySpan`1<uint8>,bool)[MinOptJitted]

Actual behavior

An entry for System.ConsolePal::Writ exists, even though there is no such method. Here's an example entry:

0x7fb99c69d090 22a void [System.Console] System.ConsolePal::Writ(class [System.Runtime]Microsoft.Win32.SafeHandles.SafeFileHandle,valuetype [System.Runtime]System.ReadOnlySpan`1<uint8>,bool)[MinOptJitted]

Regression?

Yes. This is a regression from #81243.

This was subsequently fixed in .NET 9 via #98687. I have confirmed that applying this PR to .NET 8 fixes the problem. Requesting that we backport this change to .NET 8.

Known Workarounds

None.

Configuration

• All versions of .NET 8.
• All architectures.
• Linux only.

Other information

No response