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stdio-common: Introduce buffers for implementing printf

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These buffers will eventually be used instead of FILE * objects
to implement printf functions.  The multibyte buffer is struct
__printf_buffer, the wide buffer is struct __wprintf_buffer.

To enable writing type-generic code, the header files
printf_buffer-char.h and printf_buffer-wchar_t.h define the
Xprintf macro differently, enabling Xprintf (buffer) to stand
for __printf_buffer and __wprintf_buffer as appropriate.  For
common cases, macros like Xprintf_buffer are provided as a more
syntactically convenient shortcut.

Buffer-specific flush callbacks are implemented with a switch
statement instead of a function pointer, to avoid hardening issues
similar to those of libio vtables.  struct __printf_buffer_as_file
is needed to support custom printf specifiers because the public
interface for that requires passing a FILE *, which is why there
is a trapdoor back from these buffers to FILE * streams.

Since the immediate user of these interfaces knows when processing
has finished, there is no flush callback for the end of processing,
only a flush callback for the intermediate buffer flush.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
This commit is contained in:
Florian Weimer
2022-12-19 18:56:54 +01:00
parent ffde06c915
commit 659fe9fdd1
29 changed files with 1534 additions and 0 deletions
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36
stdio-common/wprintf_buffer_flush.c Normal file
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/* Flush a struct __wprintf_buffer. Wide version.
Copyright (C) 2022 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 <printf_buffer.h>
#include "printf_buffer-wchar_t.h"
#include "Xprintf_buffer_flush.c"
static void
__wprintf_buffer_do_flush (struct __wprintf_buffer *buf)
{
switch (buf->mode)
{
case __wprintf_buffer_mode_failed:
return;
case __wprintf_buffer_mode_to_file:
__wprintf_buffer_flush_to_file ((struct __wprintf_buffer_to_file *) buf);
return;
}
__builtin_trap ();
}