Write perfmap and jitdump files to /tmp by default [6.0 port]

[tommcdon]

Description

Perfmaps and Jitdumps is a Linux kernel feature that allows .NET to symbolicate dynamically generated code with perf_events. The perfmap/jitdump files are processed by the the Linux perf tool to generate human readable callstacks for CPU traces, for example. The Linux implementation looks for the perfmap/jitdump files in /tmp (please see https://elixir.bootlin.com/linux/v6.4.3/source/tools/perf/util/symbol.c#L1838). The .NET implementation defaults to writing to /tmp but this can be overridden with the $TMPDIR environment variable. This leads to incorrect behavior in environments where $TMPDIR is in use. This code change alters the behavior and will use /tmp regardless of $TMPDIR settings. There is a minor fix included with this change that correctly sets perfmap location if DOTNET_PerfMapJitDumpPath is set.

This is a port of #88776 from .NET 8

Customer Impact

Internal partner teams have requested this change in .NET servicing

Regression?

Not a regression

Risk

Low, perfmaps+jitdumps is opt-in feature and we are only changing the default location where they are being written to

[carlossanlop]

@tommcdon I see this is still a draft. Reminder - Tomorrow Monday 10th is Code Complete for the August Release. If you intend to get this fix included in that servicing release, please make sure to get a Tactics approval and merge the PR before 4pm, because that's when I close the branches to start merging staging into internal.

[tommcdon]

@tommcdon I see this is still a draft. Reminder - Tomorrow Monday 10th is Code Complete for the August Release. If you intend to get this fix included in that servicing release, please make sure to get a Tactics approval and merge the PR before 4pm, because that's when I close the branches to start merging staging into internal.

Thanks @carlossanlop for the reminder. We didn't receive partner team signoff until after the snap, so we will be targeting the next servicing opportunity for .net 6.

[ghost]

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Issue Details

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Author:	tommcdon
Assignees:	tommcdon
Labels:	area-Diagnostics-coreclr, area-VM-coreclr
Milestone:	-

[jeffschwMSFT]

approved. we will take for consideration in 6.0.x