[LLVMdev] ExecutionEngine/Interpreter/ExternalFunctions.cpp

[Chris Lattner]

On Tue, 11 May 2004, Reid Spencer wrote:

> And, one more weird thing in this function. The FILESize static variable
> is never initialized so its likely initial value is 0 due to zero fill
> on many MMUs. The value is never written and used as a divisor. Why
> hasn't this function caused an arithmetic violation? Because the IOBBase
> point, also a static variable is initialized to zero and never modified
> and used in a conditional that thwarts the second if statement.

Yeah, the __iob stuff should all be eradicated.

> What was the _intent_ of all this?

The original idea was to support emulation of sparc headers on X86
machines.  The problem is that the sparc stdio.h file #defines stdin (for
example) as &__iob[0].  Any reference to stdin thus passes the pointer
into the wierd sparc-specific array instead of a global variable named
'stdin'.

On linux/glibc, stdin is a global symbol, and the __iob array doesn't
exist.  Before we had C front-end support for X86 (this was a LONG time
ago), we dynamically noticed a reference to the __iob array and mapped it
to the real stdin/out/err.  When the interpreter is running natively on
the sparc, it maps the programs __iob array onto the interpreter processes
__iob array, and everything works magically right (same with stdin ->
stdin on Linux machines).

This code is long dead, broken (as you've observed), and I would be happy
to see it go. :)

-Chris





> On Tue, 2004-05-11 at 18:28, Reid Spencer wrote:
> > I mis-stated what I think should be deleted.
> >
> > The block of code from "GlobalVariable *IOB = 0;" to the end of the loop
> > should be delted because the only effect the loop has is on the IOB
> > variable and that variable is never used after the loop.
> >
> > Reid.
> >
> > On Tue, 2004-05-11 at 18:14, Reid Spencer wrote:
> > > Hi,
> > >
> > > I'm working on bug 122, consolidating the interface to the SymbolTable
> > > class. In doing so, I found the function below which traverses the
> > > symbol table but apparently unnecessarily. Before I remove the
> > > traversal, I thought I better check with you guys. Posted this to the
> > > list because it looks like _everyone_ has edited this file :)
> > >
> > > In the code below, the IOB variable is the only thing in the loop that
> > > seems to get modified. However, it is never used in the subsequent code.
> > > Perhaps there's some subtle usage here I'm missing.  I'd like to delete
> > > all the code from the start of the function to the end of the loop.
> > >
> > > Could someone who knows check this, please?
> > >
> > > Thanks,
> > >
> > > Reid.
> > >
> > >
> > > static FILE *getFILE(void *Ptr) {
> > >   static Module *LastMod = 0;
> > >   static PointerTy IOBBase = 0;
> > >   static unsigned FILESize;
> > >
> > >   if (LastMod != &TheInterpreter->getModule()) { // Module change or initialize?
> > >     Module *M = LastMod = &TheInterpreter->getModule();
> > >
> > >     // Check to see if the currently loaded module contains an __iob symbol...
> > >     GlobalVariable *IOB = 0;
> > >     SymbolTable &ST = M->getSymbolTable();
> > >     for (SymbolTable::iterator I = ST.begin(), E = ST.end(); I != E; ++I) {
> > >       SymbolTable::VarMap &M = I->second;
> > >       for (SymbolTable::VarMap::iterator J = M.begin(), E = M.end();
> > >            J != E; ++J)
> > >         if (J->first == "__iob")
> > >           if ((IOB = dyn_cast<GlobalVariable>(J->second)))
> > >             break;
> > >       if (IOB) break;
> > >     }
> > >   }
> > >
> > >   // Check to see if this is a reference to __iob...
> > >   if (IOBBase) {
> > >     unsigned FDNum = ((unsigned long)Ptr-IOBBase)/FILESize;
> > >     if (FDNum == 0)
> > >       return stdin;
> > >     else if (FDNum == 1)
> > >       return stdout;
> > >     else if (FDNum == 2)
> > >       return stderr;
> > >   }
> > >
> > >   return (FILE*)Ptr;
> > > }
> >
> >
> > _______________________
> > Reid Spencer
> > President & CTO
> > eXtensible Systems, Inc.
> rspencer at x10sys.com
>
>
> _______________________
> Reid Spencer
> President & CTO
> eXtensible Systems, Inc.
> rspencer at x10sys.com
>

-Chris

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