From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
To: libc-alpha@sourceware.org
Subject: Re: [PATCH] vfprintf: Allocate the user argument buffer on the heap
Date: Tue, 27 Jun 2017 18:45:00 -0000 [thread overview]
Message-ID: <2be1d31c-cd05-71fe-5ab6-11e5371c1c09@linaro.org> (raw)
In-Reply-To: <20170619162016.3F506402AEC0E@oldenburg.str.redhat.com>
On 19/06/2017 13:20, Florian Weimer wrote:
> 2017-06-19 Florian Weimer <fweimer@redhat.com>
>
> * stdio-common/vfprintf.c (allocate_user_args_buffer): New
> function.
> (printf_positional): Call it.
>
> diff --git a/stdio-common/vfprintf.c b/stdio-common/vfprintf.c
> index e0c6edf..b15c5d0 100644
> --- a/stdio-common/vfprintf.c
> +++ b/stdio-common/vfprintf.c
> @@ -1618,6 +1618,26 @@ do_positional:
> return done;
> }
> \f
> +
> +
> +/* Called from printf_positional to determine the size of the user
> + argument area and allocate it, after discovering that one is
> + needed. This function returns NULL on allocation failure. */
> +static void *
> +allocate_user_args_buffer (size_t nargs, const int *args_size,
> + const int *args_type)
> +{
> + assert (__printf_va_arg_table != NULL);
> + size_t size = 0;
> + for (size_t i = 0; i < nargs; ++i)
> + if ((args_type[i] & PA_FLAG_MASK) == 0
> + && args_type[i] >= PA_LAST
> + && __printf_va_arg_table[args_type[i] - PA_LAST] != NULL)
> + size += roundup (args_size[i], _Alignof (max_align_t));
> + assert (size > 0);
> + return malloc (size);
> +}
> +
> static int
> printf_positional (_IO_FILE *s, const CHAR_T *format, int readonly_format,
> va_list ap, va_list *ap_savep, int done, int nspecs_done,
> @@ -1636,6 +1656,12 @@ printf_positional (_IO_FILE *s, const CHAR_T *format, int readonly_format,
> struct scratch_buffer argsbuf;
> scratch_buffer_init (&argsbuf);
>
> + /* Allocation area for user argument data. Lazily allocated by
> + allocate_user_args_buffer. */
> + void *user_args_buffer = NULL;
> + /* Upcoming allocation within user_args_buffer. */
> + void *user_args_buffer_next = NULL;
> +
> /* Array with information about the needed arguments. This has to
> be dynamically extensible. */
> size_t nspecs = 0;
> @@ -1796,7 +1822,34 @@ printf_positional (_IO_FILE *s, const CHAR_T *format, int readonly_format,
> else if (__glibc_unlikely (__printf_va_arg_table != NULL)
> && __printf_va_arg_table[args_type[cnt] - PA_LAST] != NULL)
> {
> - args_value[cnt].pa_user = alloca (args_size[cnt]);
> + /* Allocate from user_args_buffer. */
> + size_t allocation_size = args_size[cnt];
> + void *allocation;
> + if (allocation_size == 0)
> + /* Nothing to allocate. */
> + allocation = NULL;
> + else
> + {
> + if (user_args_buffer == NULL)
> + {
> + /* First user argument. Allocate the complete
> + buffer. */
> + user_args_buffer = allocate_user_args_buffer
> + (nargs, args_size, args_type);
> + if (user_args_buffer == NULL)
> + {
> + done = -1;
> + goto all_done;
> + }
> + user_args_buffer_next = user_args_buffer;
> + }
> + allocation = user_args_buffer_next;
> + user_args_buffer_next
> + += roundup (allocation_size, _Alignof (max_align_t));
> + }
> + /* Install the allocated pointer and use the callback to
> + extract the argument. */
> + args_value[cnt].pa_user = allocation;
> (*__printf_va_arg_table[args_type[cnt] - PA_LAST])
> (args_value[cnt].pa_user, ap_savep);
I am trying to convince myself it is worth to add all this complexity
to allocate for user defined types, but I am failing to understand why
can we just simplify it to a malloc using 'args_size[cnt]' (as the alloca
is already using it). And why do we need to keep track of the buffer
allocation after the callback track? Could we just free it after the
call?
> }
> @@ -1953,6 +2006,7 @@ printf_positional (_IO_FILE *s, const CHAR_T *format, int readonly_format,
> - specs[nspecs_done].end_of_fmt);
> }
> all_done:
> + free (user_args_buffer);
> scratch_buffer_free (&argsbuf);
> scratch_buffer_free (&specsbuf);
> return done;
>
next prev parent reply other threads:[~2017-06-27 18:45 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-19 16:20 Florian Weimer
2017-06-27 18:45 ` Adhemerval Zanella [this message]
2017-06-27 19:13 ` Florian Weimer
2017-06-27 20:04 ` Adhemerval Zanella
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