Valgrind cannot locate stack allocation for uninitialised data

Question

I have a a single error when I run my program through valgrind. The problem is that it wont tell me where the uninitialised bytes were allocated:

==22141== Syscall param write(buf) points to uninitialised byte(s)
==22141==    at 0x5B68900: __write_nocancel (syscall-template.S:82)
==22141==    by 0x5AFB882: _IO_file_write@@GLIBC_2.2.5 (fileops.c:1289)
==22141==    by 0x5AFB749: new_do_write (fileops.c:543)
==22141==    by 0x5AFCEB4: _IO_do_write@@GLIBC_2.2.5 (fileops.c:516)
==22141==    by 0x5AFDD3E: _IO_switch_to_get_mode (genops.c:189)
==22141==    by 0x5AFBA96: _IO_file_seekoff@@GLIBC_2.2.5 (fileops.c:999)
==22141==    by 0x5AF4F25: rewind (rewind.c:37)
==22141==    by 0x567D149: CBFileAppend (CBFileEC.c:69)
==22141==    by 0x5473AFA: CBDatabaseCreateDeletionIndex (CBDatabase.c:270)
==22141==    by 0x5473195: CBInitDatabase (CBDatabase.c:112)
==22141==    by 0x54721A1: CBNewAddressStorage (CBAddressStorage.c:37)
==22141==    by 0x401F67: main (testCBAddressManager.c:226)
==22141==  Address 0x402a009 is not stack'd, malloc'd or (recently) free'd
==22141==  Uninitialised value was created by a stack allocation
==22141==    at 0x546F750: ??? (in /media/sf_BitEagle_Projects/cbitcoin/bin/libcbitcoin-storage.2.0.so)

Would I be correct in assuming this means some sort of invalid pointer to the stack? This happens in rewind() and I do not understand why rewind would be like this. I tried attaching the valgrind process to gdb and I tried to print the result of the ftell() on the file pointer. This caused valgrind to exit with this:

valgrind: m_syswrap/syswrap-main.c:1296 (vgPlain_client_syscall): Assertion 'sci->status.what == SsIdle' failed.
==22938==    at 0x3804CA36: ??? (in /usr/lib/valgrind/memcheck-amd64-linux)
==22938==    by 0x3804CBDC: ??? (in /usr/lib/valgrind/memcheck-amd64-linux)
==22938==    by 0x38091F55: ??? (in /usr/lib/valgrind/memcheck-amd64-linux)
==22938==    by 0x3808E5DF: ??? (in /usr/lib/valgrind/memcheck-amd64-linux)
==22938==    by 0x3808F739: ??? (in /usr/lib/valgrind/memcheck-amd64-linux)
==22938==    by 0x3809F7D5: ??? (in /usr/lib/valgrind/memcheck-amd64-linux)

sched status:
  running_tid=1

Thread 1: status = VgTs_Runnable
==22938==    at 0x5B68900: __write_nocancel (syscall-template.S:82)
==22938==    by 0x5AFB882: _IO_file_write@@GLIBC_2.2.5 (fileops.c:1289)
==22938==    by 0x5AFB749: new_do_write (fileops.c:543)
==22938==    by 0x5AFCEB4: _IO_do_write@@GLIBC_2.2.5 (fileops.c:516)
==22938==    by 0x5AFDD3E: _IO_switch_to_get_mode (genops.c:189)
==22938==    by 0x5AFBA96: _IO_file_seekoff@@GLIBC_2.2.5 (fileops.c:999)
==22938==    by 0x5AF1AA5: ftell (ioftell.c:41)
==22938==    by 0x40133F: ??? (in /media/sf_BitEagle_Projects/cbitcoin/bin/testCBAddressManager)
==22938==    by 0xF75E467: ???
==22938==    by 0x7FEFFF3BF: ???
==22938==    by 0xF75E467: ???
==22938==    by 0x546DE87: ??? (in /media/sf_BitEagle_Projects/cbitcoin/bin/libcbitcoin-storage.2.0.so)
==22938==    by 0x7FEFFF3DF: ???

How would I go about determining the cause of this error?

Edit: I fixed the other issue I was having but this persists.

This is from the code here: https://github.com/MatthewLM/cbitcoin/blob/master/test/testCBAddressManager.c

The file IO code is here: https://github.com/MatthewLM/cbitcoin/tree/master/dependencies/storage

Thank you.

Answer 1

Syscall param write(buf) points to uninitialised byte(s)

There isn't necessarily anything wrong with that. Consider:

int main() {
  struct Foo { int a; int b; int c; } x;
  x.a = 1; x.c = 3;
  write(1, &x, sizeof(x));  // part of x is not initialized
  return 0;
}

If later you read the data back in, and only use .a and .c members, then your program is well defined.

Would I be correct in assuming this means some sort of invalid pointer to the stack?

No.

If you really wanted to find out which part of data is uninitialized, use Valgrind'd built-in gdbserver, and issue monitor check_memory defined command.