[pacman-dev] Bug in libalpm: sizeof(off_t)

[Dave Reisner]

On Thu, Dec 12, 2013 at 02:14:19AM +1000, Allan McRae wrote:
> On 12/12/13 00:24, Jeremy Heiner wrote:
> > On Tue, Dec 10, 2013 at 11:58 PM, Allan McRae <allan at archlinux.org> wrote:
> >> I am still looking for something cleaner than
> >> the proposed #define/#undef approach which feels a bit hacky
> > 
> > Here is a third (well, 4th, since "do nothing" is always on the table)
> > option which lies between "just document" and "macro shenanigans"...
> > Following the lead of 'alpm_capabilities', add:
> > 
> 
> How about #5...
> 
> 
> diff --git a/lib/libalpm/alpm.c b/lib/libalpm/alpm.c
> index 878c38b..a41c07d 100644
> --- a/lib/libalpm/alpm.c
> +++ b/lib/libalpm/alpm.c
> @@ -52,6 +52,12 @@ alpm_handle_t SYMEXPORT *alpm_initialize(const char
> *root, const char *dbpath,
>  	const char *lf = "db.lck";
>  	size_t lockfilelen;
>  	alpm_handle_t *myhandle = _alpm_handle_new();
> +
> +	/* calculate off_t size at runtime */
> +	size_t off_t_size = ((char *)((off_t *)0 + 1) - (char *)(off_t *)0);
> +
> +	if(off_t_size != sizeof(off_t)) {
> +		myerr = ALPM_ERR_OFF_T_SIZE;
> +		goto cleanup;
> +	}

I do not believe this actually works as intended. There's nothing "at
runtime" about this, especially when optimizations are involved (even
with -O1). Your off_t_size will be calculated at compile time and
therefore the comparison that follows will never fail. The instructions
generated for the off_t_size is effectively:

    mov    $0x8,%eax

Or, when LFS isn't enabled:

    mov   $0x4,%eax

d

> 
>  	if(myhandle == NULL) {
>  		myerr = ALPM_ERR_MEMORY;
> diff --git a/lib/libalpm/alpm.h b/lib/libalpm/alpm.h
> index 5fa775c..f61e3f5 100644
> --- a/lib/libalpm/alpm.h
> +++ b/lib/libalpm/alpm.h
> @@ -1333,6 +1333,7 @@ typedef enum _alpm_errno_t {
>  	/* Misc */
>  	ALPM_ERR_RETRIEVE,
>  	ALPM_ERR_INVALID_REGEX,
> +	ALPM_ERR_OFF_T_SIZE,
>  	/* External library errors */
>  	ALPM_ERR_LIBARCHIVE,
>  	ALPM_ERR_LIBCURL,
> diff --git a/lib/libalpm/error.c b/lib/libalpm/error.c
> index 8622180..1aed1a1 100644
> --- a/lib/libalpm/error.c
> +++ b/lib/libalpm/error.c
> @@ -145,6 +145,8 @@ const char SYMEXPORT *alpm_strerror(alpm_errno_t err)
>  			return _("failed to retrieve some files");
>  		case ALPM_ERR_INVALID_REGEX:
>  			return _("invalid regular expression");
> +		case ALPM_ERR_OFF_T_SIZE:
> +			return _("incompatible off_t size");
>  		/* Errors from external libraries- our own wrapper error */
>  		case ALPM_ERR_LIBARCHIVE:
>  			/* it would be nice to use archive_error_string() here, but that
> 
> 
>