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JIT: some jumps based on uninitialized values detected by valgrind #46961

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BruceForstall opened this issue Jan 14, 2021 · 0 comments · Fixed by #46965
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JIT: some jumps based on uninitialized values detected by valgrind #46961

BruceForstall opened this issue Jan 14, 2021 · 0 comments · Fixed by #46965
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area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI
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6.0.0

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@BruceForstall
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From @tmds, #46905

I ran valgrind on dotnet hello world, and it pointed out a few jumps based on uninitialized values.

  1. LinearScan::buildIntervals() (src/coreclr/jit/lsrabuild.cpp:2320)

runtime/src/coreclr/jit/lsrabuild.cpp

Line 2320 in b95de55

if (firstColdLoc == MaxLocation)

It looks like firstColdLoc is only initialized in DEBUG. Probably it should be also set to MaxLocation in release?

runtime/src/coreclr/jit/lsra.cpp

Lines 719 to 721 in b95de55

#ifdef DEBUG
maxNodeLocation = 0;
firstColdLoc = MaxLocation;

  1. FindConstReturnBlock (src/coreclr/jit/flowgraph.cpp:9189)

runtime/src/coreclr/jit/flowgraph.cpp

Line 9189 in b95de55

if (returnConstants[i] == constVal)

returnConstants[i] is not initialized. I don't know what the best place is to initialize it.

  1. CodeGen::instGen(instruction) (src/coreclr/jit/instr.cpp:200)

runtime/src/coreclr/jit/instr.cpp

Line 200 in 36d132e

if (ins == INS_lock && GetEmitter()->emitNextNop == 0)

emitNextNop initialization is tied to PSEUDORANDOM_NOP_INSERTION, so this check should probably #ifdef PSEUDORANDOM_NOP_INSERTION?
@BruceForstall BruceForstall added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label Jan 14, 2021
@BruceForstall BruceForstall added this to the 6.0.0 milestone Jan 14, 2021
@BruceForstall BruceForstall self-assigned this Jan 14, 2021
@dotnet-issue-labeler dotnet-issue-labeler bot added the untriaged New issue has not been triaged by the area owner label Jan 14, 2021
@BruceForstall BruceForstall mentioned this issue Jan 14, 2021
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@BruceForstall BruceForstall removed the untriaged New issue has not been triaged by the area owner label Jan 14, 2021
BruceForstall added a commit to BruceForstall/runtime that referenced this issue Jan 14, 2021
@BruceForstall
Fix uses of uninitialized data
303fe94 
Fixes dotnet#46961
@BruceForstall BruceForstall mentioned this issue Jan 14, 2021
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@ghost ghost added the in-pr There is an active PR which will close this issue when it is merged label Jan 14, 2021
BruceForstall added a commit that referenced this issue Jan 15, 2021
@BruceForstall
Fix uses of uninitialized data (#46965)
e3247ad 
* Fix uses of uninitialized data

Fixes #46961

* Fix typo

* Formatting
@ghost ghost removed the in-pr There is an active PR which will close this issue when it is merged label Jan 15, 2021
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Fix uses of uninitialized data BruceForstall/runtime
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