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* fix null pointer subtraction and comparison in stdioRich Felker2018-09-161-1/+1
| | | | | | | | | | | | | | | | | | | | morally, for null pointers a and b, a-b, a<b, and a>b should all be defined as 0; however, C does not define any of them. the stdio implementation makes heavy use of such pointer comparison and subtraction for buffer logic, and also uses null pos/base/end pointers to indicate that the FILE is not in the corresponding (read or write) mode ready for accesses through the buffer. all of the comparisons are fixed trivially by using != in place of the relational operators, since the opposite relation (e.g. pos>end) is logically impossible. the subtractions have been reviewed to check that they are conditional the stream being in the appropriate reading- or writing-through-buffer mode, with checks added where needed. in fgets and getdelim, the checks added should improve performance for unbuffered streams by avoiding a do-nothing call to memchr, and should be negligible for buffered streams.
* hide purely dependency-triggering functions in stdio __toread & __towriteRich Felker2018-09-121-1/+1
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* move __stdio_exit_needed to stdio_impl.hRich Felker2018-09-121-2/+0
| | | | this functions is glue for linking dependency logic.
* fix undefined pointer comparison in stdio-internal __toreadRich Felker2016-03-281-1/+1
| | | | | | | | | | | | | | the comparison f->wpos > f->buf has undefined behavior when f->wpos is a null pointer, despite the intuition (and actual compiler behavior, for all known compilers) being that NULL > ptr is false for all valid pointers ptr. the purpose of the comparison is to determine if the write buffer is non-empty, and the idiom used elsewhere for that is comparison against f->wbase, which is either a null pointer when not writing, or equal to f->buf when writing. in the former case, both f->wpos and f->wbase are null; in the latter they are both non-null and point into the same array.
* fix failure of ungetc and ungetwc to work on files in eof statusRich Felker2015-05-291-4/+4
| | | | | | | | | | | | | | | | | | | | | | | these functions were written to handle clearing eof status, but failed to account for the __toread function's handling of eof. with this patch applied, __toread still returns EOF when the file is in eof status, so that read operations will fail, but it also sets up valid buffer pointers for read mode, which are set to the end of the buffer rather than the beginning in order to make the whole buffer available to ungetc/ungetwc. minor changes to __uflow were needed since it's now possible to have non-zero buffer pointers while in eof status. as made, these changes remove a 'fast path' bypassing the function call to __toread, which could be reintroduced with slightly different logic, but since ordinary files have a syscall in f->read, optimizing the code path does not seem worthwhile. the __stdio_read function is also updated not to zero the read buffer pointers on eof/error. while not necessary for correctness, this change avoids the overhead of calling __toread in ungetc after reaching eof, and it also reduces code size and increases consistency with the fmemopen read operation which does not zero the pointers.
* simplify __stdio_exit static linking logicRich Felker2014-07-161-6/+3
| | | | | | | | | | | | | | | | | | | the purpose of this logic is to avoid linking __stdio_exit unless any stdio reads (which might require repositioning the file offset at exit time) or writes (which might require flushing at exit time) could have been performed. previously, exit called two wrapper functions for __stdio_exit named __flush_on_exit and __seek_on_exit. both of these functions actually performed both tasks (seek and flushing) by calling the underlying __stdio_exit. in order to avoid doing this twice, an overridable data object __towrite_used was used to cause __seek_on_exit to act as a nop when __towrite was linked. now, exit only makes one call, directly to __stdio_exit. this is satisfiable by a weak dummy definition in exit.c, but the real definition is pulled in by either __toread.c or __towrite.c through their referencing a symbol which is defined only in __stdio_exit.c.
* fix missing function declarations for __stdio_exitRich Felker2012-07-021-0/+2
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* stdio: handle file position correctly at program exitRich Felker2012-06-191-0/+8
| | | | | | | | | | | | | | | | for seekable files, posix imposed requirements on the offset of the underlying open file description after a stream is closed. this was correctly handled (as a side effect of the unconditional fflush call) when streams were explicitly closed by fclose, but was not handled correctly at program exit time, where fflush(0) was being used. the weak symbol hackery is to pull in __stdio_exit if either of __toread or __towrite is used, but avoid calling it twice so we don't have to keep extra state. the new __stdio_exit is a streamlined fflush variant that avoids performing any unnecessary operations and which never unlocks the files or open file list, so we can be sure no other threads write new data to a stream's buffer after it's already flushed.
* major stdio overhaul, using readv/writev, plus other changesRich Felker2011-03-281-0/+14
the biggest change in this commit is that stdio now uses readv to fill the caller's buffer and the FILE buffer with a single syscall, and likewise writev to flush the FILE buffer and write out the caller's buffer in a single syscall. making this change required fundamental architectural changes to stdio, so i also made a number of other improvements in the process: - the implementation no longer assumes that further io will fail following errors, and no longer blocks io when the error flag is set (though the latter could easily be changed back if desired) - unbuffered mode is no longer implemented as a one-byte buffer. as a consequence, scanf unreading has to use ungetc, to the unget buffer has been enlarged to hold at least 2 wide characters. - the FILE structure has been rearranged to maintain the locations of the fields that might be used in glibc getc/putc type macros, while shrinking the structure to save some space. - error cases for fflush, fseek, etc. should be more correct. - library-internal macros are used for getc_unlocked and putc_unlocked now, eliminating some ugly code duplication. __uflow and __overflow are no longer used anywhere but these macros. switch to read or write mode is also separated so the code can be better shared, e.g. with ungetc. - lots of other small things.