[Toybox] [PATCH] xargs: fix for 32-bit.

[enh]

ping?

On Fri, Jul 26, 2019 at 2:32 PM enh <enh at google.com> wrote:
>
> This affects both arm and x86, causing a signed comparison rather than
> an unsigned one.
>
> Here's arm:
>
>       if (data <= (char *)2) data = 0;
>    51ecc:       2902            cmp     r1, #2
>    51ece:       d905            bls.n   51edc <xargs_main+0x158>
>
>       if ((long)data <= 2) data = 0;
>    51ecc:       2902            cmp     r1, #2
>    51ece:       dc02            bgt.n   51ed6 <xargs_main+0x152>
>
> And x86 was similiar (and was where I first stumbled across this bug):
>
>       if (data <= (char *)2) data = 0;
>    73ad7:       83 f8 02                cmp    $0x2,%eax
>    73ada:       76 12                   jbe    73aee <xargs_main+0x223>
>
>       if ((long)data <= 2) data = 0;
>    73ad7:       83 f8 02                cmp    $0x2,%eax
>    73ada:       7e 12                   jle    73aee <xargs_main+0x223>
>
> For some reason, on the desktop I seem to see heap addresses low enough
> to not appear negative, whereas Android seems to fail every time.
> jemalloc is presumably more likely to allocate high?
>
> While I'm here, make it clearer that we're ignoring the allocated length
> argument to getdelim(), and stop storing the actual length at all
> because we don't use it afterwards. This wasn't _wrong_, but it was a
> red herring when I started debugging.
> ---
>  toys/posix/xargs.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)