Re: [PATCH 10/11] stdio-common: Support large offsets with %lln

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

On 09/02/24 12:25, Florian Weimer wrote:
> Use of Xprintf_buffer_done is unnecessary because it performs
> overflow detection against int and sets errno.
> ---
>  stdio-common/Makefile               |  1 +
>  stdio-common/tst-printf-large-n.c   | 81 +++++++++++++++++++++++++++++
>  stdio-common/vfprintf-process-arg.c |  2 +-
>  3 files changed, 83 insertions(+), 1 deletion(-)
>  create mode 100644 stdio-common/tst-printf-large-n.c
> 
> diff --git a/stdio-common/Makefile b/stdio-common/Makefile
> index d610ed67e6..482d841f96 100644
> --- a/stdio-common/Makefile
> +++ b/stdio-common/Makefile
> @@ -234,6 +234,7 @@ tests := \
>    tst-printf-fp-free \
>    tst-printf-fp-leak \
>    tst-printf-intn \
> +  tst-printf-large-n \
>    tst-printf-oct \
>    tst-printf-round \
>    tst-printfsz \
> diff --git a/stdio-common/tst-printf-large-n.c b/stdio-common/tst-printf-large-n.c
> new file mode 100644
> index 0000000000..4504a693d2
> --- /dev/null
> +++ b/stdio-common/tst-printf-large-n.c
> @@ -0,0 +1,81 @@
> +/* Test that %n can report values larger than INT_MAX.
> +   Copyright (C) 2024 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <errno.h>
> +#include <limits.h>
> +#include <stdio.h>
> +#include <wchar.h>
> +
> +#include <support/blob_repeat.h>
> +#include <support/check.h>
> +#include <support/xstdio.h>
> +
> +static int
> +do_test (void)
> +{
> +  enum { string_length = 1 << 28 };
> +
> +  FILE *fp = xfopen ("/dev/null", "w");
> +
> +  /* Byte-oriented streams.  */
> +  {
> +    struct support_blob_repeat repeat
> +      = support_blob_repeat_allocate ("a", 1, string_length + 1);
> +    char *string = repeat.start;
> +    if (string == NULL)
> +      FAIL_UNSUPPORTED ("cannot allocate large string");
> +    string[string_length] = '\0';
> +
> +      long long int n;

Indentation seems off here.

> +    TEST_COMPARE (fprintf (fp, "%s %s %s %s %s %s %s %s %lln",
> +                           string, string, string, string, string, string,
> +                           string, string, &n), -1);
> +    TEST_COMPARE (errno, EOVERFLOW);
> +    TEST_COMPARE (n, 8 * (string_length + 1LL));
> +    TEST_VERIFY (n > INT_MAX);
> +
> +      support_blob_repeat_free (&repeat);

Here as well.

> +  }
> +
> +  /* Wide-oriented streams.  */
> +  {
> +    struct support_blob_repeat repeat
> +      = support_blob_repeat_allocate (L"a", sizeof (wchar_t),
> +                                      string_length + 1);
> +    wchar_t *string = repeat.start;
> +    if (string == NULL)
> +      FAIL_UNSUPPORTED ("cannot allocate large wide string");
> +    string[string_length] = '\0';

It should not matter, but maybe L'\0' here?

> +
> +    long long int n;
> +    TEST_COMPARE (fwprintf (fp, L"%Ls %Ls %Ls %Ls %Ls %Ls %Ls %Ls %lln",
> +                            string, string, string, string, string, string,
> +                            string, string, &n), -1);
> +    TEST_COMPARE (errno, EOVERFLOW);
> +    TEST_COMPARE (n, 8 * (string_length + 1LL));
> +    TEST_VERIFY (n > INT_MAX);
> +
> +      support_blob_repeat_free (&repeat);
> +  }
> +
> +  xfclose (fp);
> +
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>
> diff --git a/stdio-common/vfprintf-process-arg.c b/stdio-common/vfprintf-process-arg.c
> index af6b570ea9..dbc78d4942 100644
> --- a/stdio-common/vfprintf-process-arg.c
> +++ b/stdio-common/vfprintf-process-arg.c
> @@ -337,7 +337,7 @@ LABEL (form_number):
>      }
>    /* Answer the count of characters written.  */
>    void *ptrptr = process_arg_pointer ();
> -  unsigned int written = Xprintf_buffer_done (buf);
> +  uint64_t written = buf->written + (buf->write_ptr - buf->write_base);
>    if (is_longlong)
>      *(long long int *) ptrptr = written;
>    else if (is_long_num)

This is strictly an alias violation, but the rest of the code follow this
pattern so it should be ok.