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Date: Thu, 15 Sep 2016 21:14:56 +0300
From: "Dmitry V. Levin" <ldv@...linux.org>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] fix printf regression with alt-form octal, default precision
On Thu, Sep 15, 2016 at 12:37:57PM -0400, Rich Felker wrote:
> On Thu, Aug 04, 2016 at 04:07:40AM +0300, Dmitry V. Levin wrote:
> > commit v1.1.5-10-gb91cdbe2bc8b626aa04dc6e3e84345accf34e4b1 that fixed
> > behavior of printf with alt-form octal, zero precision, zero value,
> > at the same time broke alt-form octal with default precision,
> > e. g. printf("%#09o", 1).
> > ---
> > src/stdio/vfprintf.c | 9 ++++++++-
> > 1 file changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/src/stdio/vfprintf.c b/src/stdio/vfprintf.c
> > index 2ecf769..ac2891c 100644
> > --- a/src/stdio/vfprintf.c
> > +++ b/src/stdio/vfprintf.c
> > @@ -570,7 +570,14 @@ static int printf_core(FILE *f, const char *fmt, va_list *ap, union arg *nl_arg,
> > if (0) {
> > case 'o':
> > a = fmt_o(arg.i, z);
> > - if ((fl&ALT_FORM) && p<z-a+1) p=z-a+1;
> > + if (fl&ALT_FORM) {
> > + if (p >= 0 && p<z-a+1) {
> > + p=z-a+1;
> > + } else if (arg.i) {
> > + prefix+=5;
> > + pl=1;
> > + }
> > + }
> > } if (0) {
> > case 'd': case 'i':
> > pl=1;
>
> I think the attached simpler patch should work just as well. Adjusting
> 'p' to implement '#' was probably a bad idea since it makes the later
> code paths think an explicit precision was specified when it was not.
> "Add a prefix of '0' when p is too short to have a leading '0'
> already" seems like safer logic.
>
> I'm also attaching some test cases I ran.
>
> Rich
>
> diff --git a/src/stdio/vfprintf.c b/src/stdio/vfprintf.c
> index 2ecf769..e439a07 100644
> --- a/src/stdio/vfprintf.c
> +++ b/src/stdio/vfprintf.c
> @@ -570,7 +570,7 @@ static int printf_core(FILE *f, const char *fmt, va_list *ap, union arg *nl_arg,
> if (0) {
> case 'o':
> a = fmt_o(arg.i, z);
> - if ((fl&ALT_FORM) && p<z-a+1) p=z-a+1;
> + if ((fl&ALT_FORM) && p<z-a+1) prefix+=5, pl=1;
> } if (0) {
> case 'd': case 'i':
> pl=1;
Yes, this also works, thanks.
--
ldv
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