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Add support of JITDUMP_USE_ARCH_TIMESTAMP to perfjitdump. #111359

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Jan 17, 2025
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Add support of JITDUMP_USE_ARCH_TIMESTAMP to perfjitdump. #111359

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30 changes: 29 additions & 1 deletion src/coreclr/pal/src/misc/perfjitdump.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,10 @@

#include "../inc/llvm/ELF.h"

#if defined(HOST_AMD64)
#include <x86intrin.h>
#endif

SET_DEFAULT_DEBUG_CHANNEL(MISC);

namespace
Expand All @@ -37,6 +41,7 @@ namespace
{
JIT_DUMP_MAGIC = 0x4A695444,
JIT_DUMP_VERSION = 1,
JITDUMP_FLAGS_ARCH_TIMESTAMP = 1 << 0,

#if defined(HOST_X86)
ELF_MACHINE = EM_386,
Expand All @@ -61,13 +66,36 @@ namespace
JIT_CODE_LOAD = 0,
};

static bool UseArchTimeStamp()
{
static bool initialized = false;
static bool useArchTimestamp = false;

if (!initialized)
{
#if defined(HOST_AMD64)
const char* archTimestamp = getenv("JITDUMP_USE_ARCH_TIMESTAMP");
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Instead of using getenv() directly you can add this to the other config settings the runtime supports:

  1. Declare a config value in configvalues.h. Here is an example that uses the 'DontPrependPrefix' flag to declare an env var without the DOTNET_ prefix:
    https://github.com/dotnet/runtime/blob/main/src/coreclr/inc/clrconfigvalues.h#L426

  2. Use CLRConfig::GetConfigValue(CLRConfig::) to retrieve the value. Example:

    runtime/src/coreclr/vm/profilinghelper.cpp

    Line 634 in cea112c

    fProfEnabled = CLRConfig::GetConfigValue(CLRConfig::EXTERNAL_CORECLR_ENABLE_PROFILING);

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I think it would have to be CLRConfigNoCache::Get("JITDUMP_USE_ARCH_TIMESTAMP", /*noprefix*/ true, &getenv) to avoid layering issues with PAL. When this method is called with noprefix=true, it just calls getenv without anything extra.

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Thanks @jkotas! - I missed the pal layering aspect in there.

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Does this mean i dont have to update the configvalue.h and simply change the getenv method with what @jkotas said.

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I think calling getenv directly looks better.

useArchTimestamp = (archTimestamp != nullptr && strcmp(archTimestamp, "1") == 0);
#endif
initialized = true;
}

return useArchTimestamp;
}

static uint64_t GetTimeStampNS()
{
#if defined(HOST_AMD64)
if (UseArchTimeStamp()) {
return static_cast<uint64_t>(__rdtsc());
}
#endif
LARGE_INTEGER result;
QueryPerformanceCounter(&result);
return result.QuadPart;
}


struct FileHeader
{
FileHeader() :
Expand All @@ -78,7 +106,7 @@ namespace
pad1(0),
pid(getpid()),
timestamp(GetTimeStampNS()),
flags(0)
flags(UseArchTimeStamp() ? JITDUMP_FLAGS_ARCH_TIMESTAMP : 0)
{}

uint32_t magic;
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