Luca Carlon Luca Carlon - 1 month ago 21
C++ Question

Using SQLite custom functions with Qt

I'm trying to create a custom function for a SQLite database I'm using with Qt. I found information on how to create the function and it seems to work correctly on a x86 system.

Instead, it seems to be failing with a segfault on an ARM device. This is the code I wrote:

static bool createSQLiteFunctions(const QSqlDatabase& db)
{
// Get handle to the driver and check it is both valid and refers to SQLite3.
QVariant v = db.driver()->handle();
if (!v.isValid() || qstrcmp(v.typeName(), "sqlite3*") != 0) {
LOG_WARNING("Cannot get a sqlite3 handle to the driver.");
return false;
}

// Create a handler and attach functions.
sqlite3* handler = *static_cast<sqlite3**>(v.data());
if (!handler) {
LOG_WARNING("Cannot get a sqlite3 handler.");
return false;
}

// Check validity of the state.
if (!db.isValid()) {
LOG_ERROR("Cannot create SQLite custom functions: db object is not valid.");
return false;
}

if (!db.isOpen()) {
LOG_ERROR("Cannot create SQLite custom functions: db object is not open.");
return false;
}

if (sqlite3_create_function(handler, "_deleteFile", 1, SQLITE_ANY, 0, &_sqlite3DeleteFile, 0, 0))
LOG_ERROR("Cannot create SQLite functions: sqlite3_create_function failed.");

return true;
}


The db object is instantiated as a member of another object, which is calling this function in the constructor, where the connection to the db is established (multiple instances may be created concurrently, but sqlite3 is compiled with thread-safe option).
It seems that no error log is printed and, but the sqlite3_create_function function gives a segfault. If I remove the call to createSQLiteFunctions everything works fine.
Any idea why the result is a segfault?
Thanks!

Answer

If it's failing on ARM, it may have to do something with compilation (what sqlite3 are you using?) or with the callback function itself (_sqlite3DeleteFile). How is it defined, where is it located / linked. Depending on the ARM (what ARM are you using) the processor can be very picky with alignment. Check your map file, perhaps the MMU-configuration, ...?

BTW: I would probably prefer to leave out the const, as we are modifying the db.

static bool createSQLiteFunctions(/*const*/ QSqlDatabase& db)

Can you debug-step into the sqlite3_create_function code? Can you produce a trace?

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