Re: [PATCH 09/11] stdio-common: Allow skipping initial bytes in __printf_buffer for %n

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

On 09/02/24 12:25, Florian Weimer wrote:
> Making the written field signed allows subtraction of a prefix count
> in case multiple writes happen to the same buffer.

LGTM, thanks.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
>  include/printf_buffer.h          |  8 +++++---
>  stdio-common/tst-printf_buffer.c | 18 ++++++++++++++++++
>  2 files changed, 23 insertions(+), 3 deletions(-)
> 
> diff --git a/include/printf_buffer.h b/include/printf_buffer.h
> index a5483e8a97..2400371b94 100644
> --- a/include/printf_buffer.h
> +++ b/include/printf_buffer.h
> @@ -92,8 +92,10 @@ struct __printf_buffer
>       buffer).  Potentially updated on flush.  The actual number of
>       written bytes also includes the unflushed-but-written buffer
>       part, write_ptr - write_base.  A 64-bit value is used to avoid
> -     the need for overflow checks.  */
> -  uint64_t written;
> +     the need for intermediate overflow checks.  Negative values can
> +     be used to ignore leading parts of the buffer for %n computations
> +     (for repeated __printf_buffer calls to the same buffer).  */
> +  int64_t written;
>  
>    /* Identifies the flush callback.  */
>    enum __printf_buffer_mode mode;
> @@ -225,7 +227,7 @@ struct __wprintf_buffer
>    wchar_t *write_base;
>    wchar_t *write_ptr;
>    wchar_t *write_end;
> -  uint64_t written;
> +  int64_t written;
>    enum __wprintf_buffer_mode mode;
>  };
>  
> diff --git a/stdio-common/tst-printf_buffer.c b/stdio-common/tst-printf_buffer.c
> index d12da8c939..2a3ee511d0 100644
> --- a/stdio-common/tst-printf_buffer.c
> +++ b/stdio-common/tst-printf_buffer.c
> @@ -132,6 +132,24 @@ do_test (void)
>      TEST_VERIFY (!__printf_buffer_has_failed (&buf.base));
>      TEST_COMPARE (__printf_buffer_asprintf_free (&buf), -1);
>    }
> +
> +  /* Test %n with initial skip.  */
> +  {
> +    struct __printf_buffer_asprintf buf;
> +    __printf_buffer_asprintf_init (&buf);
> +    __printf_buffer (&buf.base, "abc");
> +    buf.base.written = -2;
> +    int n = -1;
> +    __printf_buffer (&buf.base, "D%nEF", &n);
> +    TEST_COMPARE (n, 2);        /* Two characters were skipped.  */
> +    TEST_VERIFY (buf.base.write_base == buf.direct);
> +    TEST_COMPARE_BLOB (buf.base.write_base,
> +                       buf.base.write_ptr - buf.base.write_base, "abcDEF", 6);
> +    TEST_VERIFY (!__printf_buffer_has_failed (&buf.base));
> +    TEST_COMPARE (__printf_buffer_done (&buf.base), 4); /* Two skipped.  */
> +    TEST_COMPARE (__printf_buffer_asprintf_free (&buf), -1);
> +  }
> +
>    return 0;
>  }
>