tursodatabase / libsql

Hi folks,

I was enjoying the recent addition of extension loading. Everything worked smoothly with the simple "sqlite/ext/misc/uuid.c".

However, when building in release mode, I suddenly get a segmentation fault. I played with the different build profiles to further narrow it down. Even when building with debug presets and just bumping opt-level from zero to one, does it for me.

Throwing it in the debugger leads to

Thread 1 "libsql" received signal SIGSEGV, Segmentation fault.
0x00005555558d91fc in sqlite3_db_config (db=0x555555bb9c38, op=<optimized out>) at bundled/src/sqlite3.c:180105
bt
180105              *pRes = (db->flags & aFlagOp[i].mask)!=0;
(gdb) bt
#0  0x00005555558d91fc in sqlite3_db_config (db=0x555555bb9c38, op=<optimized out>) at bundled/src/sqlite3.c:180105
#1  0x0000555555628518 in libsql::local::connection::Connection::enable_load_extension (self=<optimized out>, onoff=false) at vendor/libsql/libsql/src/local/connection.rs:296
#2  libsql::local::impls::{impl#4}::enable_load_extension (self=<optimized out>, onoff=false) at vendor/libsql/libsql/src/local/impls.rs:70
#3  0x0000555555603066 in libsql::connection::Connection::load_extension_enable (self=<optimized out>) at vendor/libsql/libsql/src/connection.rs:142
#4  0x00005555555ea19b in libsql::main::{async_block#0} () at src/libsql.rs:12

or the entire function in question

/*
** Configuration settings for an individual database connection
*/
SQLITE_API int sqlite3_db_config(sqlite3 *db, int op, ...){
  va_list ap;
  int rc;

#ifdef SQLITE_ENABLE_API_ARMOR
  if( !sqlite3SafetyCheckOk(db) ) return SQLITE_MISUSE_BKPT;
#endif
  sqlite3_mutex_enter(db->mutex);
  va_start(ap, op);
  switch( op ){
    case SQLITE_DBCONFIG_MAINDBNAME: {
      /* IMP: R-06824-28531 */
      /* IMP: R-36257-52125 */
      db->aDb[0].zDbSName = va_arg(ap,char*);
      rc = SQLITE_OK;
      break;
    }
    case SQLITE_DBCONFIG_LOOKASIDE: {
      void *pBuf = va_arg(ap, void*); /* IMP: R-26835-10964 */
      int sz = va_arg(ap, int);       /* IMP: R-47871-25994 */
      int cnt = va_arg(ap, int);      /* IMP: R-04460-53386 */
      rc = setupLookaside(db, pBuf, sz, cnt);
      break;
    }
    default: {
      static const struct {
        int op;      /* The opcode */
        u32 mask;    /* Mask of the bit in sqlite3.flags to set/clear */
      } aFlagOp[] = {
        { SQLITE_DBCONFIG_ENABLE_FKEY,           SQLITE_ForeignKeys    },
        { SQLITE_DBCONFIG_ENABLE_TRIGGER,        SQLITE_EnableTrigger  },
        { SQLITE_DBCONFIG_ENABLE_VIEW,           SQLITE_EnableView     },
        { SQLITE_DBCONFIG_ENABLE_FTS3_TOKENIZER, SQLITE_Fts3Tokenizer  },
        { SQLITE_DBCONFIG_ENABLE_LOAD_EXTENSION, SQLITE_LoadExtension  },
        { SQLITE_DBCONFIG_NO_CKPT_ON_CLOSE,      SQLITE_NoCkptOnClose  },
        { SQLITE_DBCONFIG_ENABLE_QPSG,           SQLITE_EnableQPSG     },
        { SQLITE_DBCONFIG_TRIGGER_EQP,           SQLITE_TriggerEQP     },
        { SQLITE_DBCONFIG_RESET_DATABASE,        SQLITE_ResetDatabase  },
        { SQLITE_DBCONFIG_DEFENSIVE,             SQLITE_Defensive      },
        { SQLITE_DBCONFIG_WRITABLE_SCHEMA,       SQLITE_WriteSchema|
                                                 SQLITE_NoSchemaError  },
        { SQLITE_DBCONFIG_LEGACY_ALTER_TABLE,    SQLITE_LegacyAlter    },
        { SQLITE_DBCONFIG_DQS_DDL,               SQLITE_DqsDDL         },
        { SQLITE_DBCONFIG_DQS_DML,               SQLITE_DqsDML         },
        { SQLITE_DBCONFIG_LEGACY_FILE_FORMAT,    SQLITE_LegacyFileFmt  },
        { SQLITE_DBCONFIG_TRUSTED_SCHEMA,        SQLITE_TrustedSchema  },
        { SQLITE_DBCONFIG_STMT_SCANSTATUS,       SQLITE_StmtScanStatus },
        { SQLITE_DBCONFIG_REVERSE_SCANORDER,     SQLITE_ReverseOrder   },
      };
      unsigned int i;
      rc = SQLITE_ERROR; /* IMP: R-42790-23372 */
      for(i=0; i<ArraySize(aFlagOp); i++){
        if( aFlagOp[i].op==op ){
          int onoff = va_arg(ap, int);
          int *pRes = va_arg(ap, int*);
          u64 oldFlags = db->flags;
          if( onoff>0 ){
            db->flags |= aFlagOp[i].mask;
          }else if( onoff==0 ){
            db->flags &= ~(u64)aFlagOp[i].mask;
          }
          if( oldFlags!=db->flags ){
            sqlite3ExpirePreparedStatements(db, 0);
          }
          if( pRes ){
            *pRes = (db->flags & aFlagOp[i].mask)!=0;
          }
          rc = SQLITE_OK;
          break;
        }
      }
      break;
    }
  }
  va_end(ap);
  sqlite3_mutex_leave(db->mutex);
  return rc;
}

I haven't looked more into it yet, since it's getting late but maybe there's something that sticks out to you folks.

Still haven't gotten around to spend much more time on this but at least I wanted to share a minimal reproduction with you: https://github.com/ignatz/libsql_ext

Hi @ignatz!
Thanks for the reproduction example - this really helps and simplify process of debugging the issue!

I guess I found an issue in libsql code but fix is rather simple (although this is pretty nasty bug, I guess): #1477

BTW, it seems to me that libsql is already build with SQLITE_ENABLE_LOAD_EXTENSION=1 (see https://github.com/tursodatabase/libsql/blob/main/libsql-ffi/build.rs#L115). So I guess you should be able to load your extensions even when bug in load_extension_enable/load_extension_disable is here.

👏

Is there any particular reason why you folks rely on sqlite3_db_config, it seems you're bindgening also the type-safe bindings:

libsql/libsql-ffi/bundled/bindings/bindgen.rs

Line 2096 in fbce426

pub fn sqlite3_enable_load_extension(

?

sqlite3_enable_load_extension works bit differently as it enables both C API and SQL function load_extension while sqlite3_db_config allow libsql to have more fine grained control over enabled features.

But actually I don't have any context here, so maybe @MarinPostma can comment on this is more details.

Segmentation fault in new extension loading API