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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>
73 lines
2.9 KiB
C
73 lines
2.9 KiB
C
/* Flush wrapper for struct __*printf_buffer. Generic version.
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Copyright (C) 2022 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <printf_buffer.h>
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#include <assert.h>
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#include <stdint.h>
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/* Xprintf (buffer_do_flush) (BUF) performs the flush operation. The
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actual implementation is specific to the multibyte and wide
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variants.
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If the flush fails, Xprintf_buffer_mark_failed (BUF) must be
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called, and BUF->write_ptr and BUF->write_end can be left
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unchanged.
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The function must not do anything if failure has already occurred,
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that is, if BUF->mode == Xprintf (buffer_mode_failed).
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The framework implicitly invokes flush with BUF->write_ptr ==
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BUF->write_end only. (This is particularly relevant to the
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__sprintf_chk flush, which just calls __chk_fail.) But in some
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cases, Xprintf_buffer_flush may be called explicitly (when
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BUF->mode/the backing function is known). In that case, it is
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possible that BUF->write_ptr < BUF->write_end is true.
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If the flush succeeds, the pointers are changed so that
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BUF->write_ptr < BUF->write_end. It is possible to switch to a
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completely different buffer here. If the buffer is moved, it may
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be necessary to updated BUF->write_base and BUF->written from the
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flush function as well.
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Note that when chaining buffers, in the flush function for the
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outer buffer (to which data is written first), it is necessary to
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check for BUF->next->failed (for the inner buffer) and set
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BUF->base.failed to true (for the outer buffer). This should come
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towards the end of the outer flush function. Usually, there is
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also some unwrapping step afterwards; it has to check the outer
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buffer (BUF->base.failed) and propagate any error to the inner
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buffer (BUF->next->failed), so essentially in the other
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direction. */
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static void Xprintf (buffer_do_flush) (struct Xprintf_buffer *buf);
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bool
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Xprintf_buffer_flush (struct Xprintf_buffer *buf)
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{
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if (__glibc_unlikely (Xprintf_buffer_has_failed (buf)))
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return false;
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Xprintf (buffer_do_flush) (buf);
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if (Xprintf_buffer_has_failed (buf))
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return false;
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/* Ensure that the flush has made available some bytes. */
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assert (buf->write_ptr != buf->write_end);
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return true;
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}
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