vfscanf() may use the variable 'alloc' uninitialized when taking the branch introduced by commit b287cd745c2243f8e5114331763a5a9813b5f6ee. Spotted by clang.
apparently this function was intended at some point to be used by strto* family as well, and thus was put in its own file; however, as far as I can tell, it's only ever been used by vsscanf. move it to the same file to reduce the number of source files and external symbols.
this idea came up when I thought we might need to zero the UNGET portion of buf as well, but it seems like a useful improvement even when that turned out not to be necessary.
as reported/analyzed by Pascal Cuoq, the shlim and shcnt macros/functions are called by the scanf core (vfscanf) with f->rpos potentially null (if the FILE is not yet activated for reading at the time of the call). in this case, they compute differences between a null pointer (f->rpos) and a non-null one (f->buf), resulting in undefined behavior. it's unlikely that any observably wrong behavior occurred in practice, at least without LTO, due to limits on what's visible to the compiler from translation unit boundaries, but this has not been checked. fix is simply ensuring that the FILE is activated for read mode before entering the main scanf loop, and erroring out early if it can't be.
this reverts commit 4ee039f3545976f9e3e25a7e5d7b58f1f2316dc3, which added the helper as a hack to make vdprintf usable before relocation, contingent on strong assumptions about the arch and tooling, back when the dynamic linker did not have a real staged model for self-relocation. since commit f3ddd173806fd5c60b3f034528ca24542aecc5b9 this has been unnecessary and the function was just wasting size and execution time.
because struct stat is no longer assumed to correspond to the structure used by the stat-family syscalls, it's not valid to make any of these syscalls directly using a buffer of type struct stat. commit 9493892021eac4edf1776d945bcdd3f7a96f6978 moved all logic around this change for stat-family functions into fstatat.c, making the others wrappers for it. but a few other direct uses of the syscall were overlooked. the ones in tmpnam/tempnam are harmless since the syscalls are just used to test for file existence. however, the uses in fchmodat and __map_file depend on getting accurate file properties, and these functions may actually have been broken one or more mips variants due to removal of conversion hacks from syscall_arch.h. as a low-risk fix, simply use struct kstat in place of struct stat in the affected places.
aside from the special value EOF, ungetc is specified to accept and convert values outside the range of unsigned char. conversion takes place automatically as part of assignment when storing into the buffer, but the return value is also required to be the resulting converted value, and this requirement was not satisfied. simplified from patch by Wang Jianjian.
commit cc3a4466605fe8dfc31f3b75779110ac93055bc1 fixed this for printf but neglected to fix wprintf. Previously, %lf caused a failure to output.
this probably saves a few bytes, avoids duplicating the clunky lseek/_llseek syscall convention in two places, and sets the stage for fixing broken seeks on x32 and mipsn32.