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Re: [PATCH] vasnprintf: Don't use %n on android


From: Hugo Beauzée-Luyssen
Subject: Re: [PATCH] vasnprintf: Don't use %n on android
Date: Mon, 21 Jan 2019 17:00:27 +0100

On Mon, Jan 21, 2019, at 4:58 PM, Tim Rühsen wrote:
> On 1/8/19 2:22 PM, Hugo Beauzée-Luyssen wrote:
> > On Thu, Dec 20, 2018, at 2:53 AM, Bruno Haible wrote:
> >> Hi,
> >>
> >> Hugo Beauzée-Luyssen wrote:
> >>> 12-14 19:10:02.633 F DEBUG   : pid: 31664, tid: 32389, name: VlcObject  
> >>> >>> org.videolan.vlc <<<
> >>> 12-14 19:10:02.633 F DEBUG   : signal 6 (SIGABRT), code -1 (SI_QUEUE), 
> >>> fault addr --------
> >>> 12-14 19:10:02.633 F DEBUG   : Abort message: 'FORTIFY: %n not allowed on 
> >>> Android'
> >>
> >> Indeed, %n in *printf is not allowed on Android, see
> >> https://android.googlesource.com/platform/bionic/+/master/libc/stdio/vfprintf.cpp
> >> https://android.googlesource.com/platform/bionic/+/master/docs/status.md
> >>
> >>> diff --git a/lib/vasnprintf.c b/lib/vasnprintf.c
> >>> index af3fcd1c7..e41d5f706 100644
> >>> --- a/lib/vasnprintf.c
> >>> +++ b/lib/vasnprintf.c
> >>> @@ -4874,7 +4874,8 @@ VASNPRINTF (DCHAR_T *resultbuf, size_t *lengthp,
> >>>  # if ! (((__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 3))     
> >>>    \
> >>>           && !defined __UCLIBC__)                                         
> >>>    \
> >>>          || (defined __APPLE__ && defined __MACH__)                       
> >>>    \
> >>> -        || (defined _WIN32 && ! defined __CYGWIN__))
> >>> +        || (defined _WIN32 && ! defined __CYGWIN__)                      
> >>>    \
> >>> +        || defined __ANDROID__)
> >>>                  fbp[1] = '%';
> >>>                  fbp[2] = 'n';
> >>>                  fbp[3] = '\0';
> >>
> >> The patch looks good at first sight. But when you look at the comments a
> >> couple of lines before it, you see that one can avoid %n only
> >> if snprintf behaves well enough. To this effect, can you please report
> >> the configure results (from a *native* Android compilation, not a cross-
> >> compilation) of these tests:
> >>
> >> 1 = checking whether printf supports size specifiers as in C99...
> >> 2 = checking whether printf supports 'long double' arguments...
> >> 3 = checking whether printf supports infinite 'double' arguments...
> >> 4 = checking whether printf supports infinite 'long double' arguments...
> >> 5 = checking whether printf supports the 'a' and 'A' directives...
> >> 6 = checking whether printf supports the 'F' directive...
> >> 7 = checking whether printf supports the 'n' directive...
> >> 8 = checking whether printf supports the 'ls' directive...
> >> 9 = checking whether printf supports POSIX/XSI format strings with 
> >> positions...
> >> 10 = checking whether printf supports the grouping flag...
> >> 11 = checking whether printf supports the left-adjust flag correctly...
> >> 12 = checking whether printf supports the zero flag correctly...
> >> 13 = checking whether printf supports large precisions...
> >> 14 = checking whether printf survives out-of-memory conditions...
> >> 15 = checking for snprintf...
> >> 16 = checking whether snprintf truncates the result as in C99...
> >> 17 = checking whether snprintf returns a byte count as in C99...
> >> 18 = checking whether snprintf fully supports the 'n' directive...
> >> 19 = checking whether snprintf respects a size of 1...
> >> 20 = checking whether vsnprintf respects a zero size as in C99...
> >>
> >> You should find these in the configure output of any package that
> >> uses gnulib's 'vasnprintf' module. If you don't have one at hand,
> >> create one using
> >>   ./gnulib-tool --create-testdir --dir=testdir --single-configure 
> >> vasnprintf
> >>
> >> Thanks.
> >>
> >> Bruno
> >>
> > 
> > Hi,
> > 
> > I'm probably missing something, but for me this only seems to test for 
> > snprintf/printf/vasnprintf availability (including running configure in the 
> > generated test directory)
> 
> I would really like to see the patch in gnulib as soon as possible.
> 
> @hugo If it's not too much hassle, could you please provide the
> requested information ?
> 
> Regards, Tim
> 

Hi,

I'd love to, but I failed to fetch those so far. The provided command line 
didn't return any valuable information, and simply tested for the presence of 
various printf family function.

Regards,

-- 
  Hugo Beauzée-Luyssen
  address@hidden



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