Subject: Re: some code assumes sizeof(char *) == sizeof(int)
To: None <>
From: Shin'ichiro TAYA <>
List: tech-pkg
Date: 02/22/2001 12:50:16
Subject: Re: some code assumes sizeof(char *) == sizeof(int)
Date: 21 Feb 2001 17:17:57 -0000

> What's a `SAVED_VAR'?

/* Structure describing a saved variable and the value to restore it to.
   If a cleanup function is set to restore_variable, the `arg' pointer
   points to this. */
typedef struct {
  int *variable;
  char *desired_setting;
  int size;

> What's the type of `sv->variable'?

int *variable;

this is a bash-2.04 source code. please refer it for detal.

> The correct fix is probably to change the macro to:
> #define unwind_protect_int(X) \
>         unwind_protect_var(&(X), (char *)(unsigned long)(X), sizeof(X))
> (The `unsigned' is optional, but correctly converts 32-bit pointers
> to 64-bit pointers.  But then we're probably not dealing with pointers
> anyway.)

I'll test this later.
But this doesn't fix warning at:

    *(sv->variable) = (int)sv->desired_setting;

because sv->desired_setting is char *, converting 64bit value to 32bit value.

> You want to use `sizeof(X)' rather than `sizeof(int)' so you can handle
> both `int' and `long', since the borken code means that they probably 
> did not distinguish the two.  

well, as macro name says, `long' will never passed to
unwind_protect_int(X), but this is good idea.

> Also: `*(sv->variable) = (int)sv->desired_setting;' is dangerous in
> this setting since it's not clear what the type of `sv->variable' is.
> You may want to add code to handle the standard scalar, and possibly
> floating point, types individually.  That way you won't need to 
> malloc() something for variables smaller than 8 (or 16) bytes.

sv->variable is used as `int', if sizeof arg is 4, otherwise
used as a pointer to a memory block alloced by malloc.