From 659fe9fdd14b0772f4e9722b751b9b010665e053 Mon Sep 17 00:00:00 2001 From: Florian Weimer Date: Mon, 19 Dec 2022 18:56:54 +0100 Subject: stdio-common: Introduce buffers for implementing printf 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 --- stdio-common/Xprintf_buffer_flush.c | 72 +++++++++++++++++++++++++++++++++++++ 1 file changed, 72 insertions(+) create mode 100644 stdio-common/Xprintf_buffer_flush.c (limited to 'stdio-common/Xprintf_buffer_flush.c') diff --git a/stdio-common/Xprintf_buffer_flush.c b/stdio-common/Xprintf_buffer_flush.c new file mode 100644 index 0000000..1368cfe --- /dev/null +++ b/stdio-common/Xprintf_buffer_flush.c @@ -0,0 +1,72 @@ +/* Flush wrapper for struct __*printf_buffer. Generic 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 + . */ + +#include + +#include +#include + +/* Xprintf (buffer_do_flush) (BUF) performs the flush operation. The + actual implementation is specific to the multibyte and wide + variants. + + If the flush fails, Xprintf_buffer_mark_failed (BUF) must be + called, and BUF->write_ptr and BUF->write_end can be left + unchanged. + + The function must not do anything if failure has already occurred, + that is, if BUF->mode == Xprintf (buffer_mode_failed). + + The framework implicitly invokes flush with BUF->write_ptr == + BUF->write_end only. (This is particularly relevant to the + __sprintf_chk flush, which just calls __chk_fail.) But in some + cases, Xprintf_buffer_flush may be called explicitly (when + BUF->mode/the backing function is known). In that case, it is + possible that BUF->write_ptr < BUF->write_end is true. + + If the flush succeeds, the pointers are changed so that + BUF->write_ptr < BUF->write_end. It is possible to switch to a + completely different buffer here. If the buffer is moved, it may + be necessary to updated BUF->write_base and BUF->written from the + flush function as well. + + Note that when chaining buffers, in the flush function for the + outer buffer (to which data is written first), it is necessary to + check for BUF->next->failed (for the inner buffer) and set + BUF->base.failed to true (for the outer buffer). This should come + towards the end of the outer flush function. Usually, there is + also some unwrapping step afterwards; it has to check the outer + buffer (BUF->base.failed) and propagate any error to the inner + buffer (BUF->next->failed), so essentially in the other + direction. */ +static void Xprintf (buffer_do_flush) (struct Xprintf_buffer *buf); + +bool +Xprintf_buffer_flush (struct Xprintf_buffer *buf) +{ + if (__glibc_unlikely (Xprintf_buffer_has_failed (buf))) + return false; + + Xprintf (buffer_do_flush) (buf); + if (Xprintf_buffer_has_failed (buf)) + return false; + + /* Ensure that the flush has made available some bytes. */ + assert (buf->write_ptr != buf->write_end); + return true; +} -- cgit v1.1