Write perfmap and jitdump files to /tmp by default

[tommcdon]

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.

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Issue Details

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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.

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

[davmason]

Thanks!

[tommcdon]

All failures are known issues, merging.