On Tuesday 08 February 2022 11:25:43 Martin Storsjö wrote: > On Sun, 6 Feb 2022, Pali Rohár wrote: > > > Currently v*scanf functions are broken and crash when are called with more > > than 30 arguments in va_list. This is because va_list v*scanf functions are > > redirected to variadic *scanf functions and this redirect implemented in > > scanf.S file has fixed limit for 30 arguments. > > > > Number of arguments for msvcrt *scanf function can be determined from > > format string by counting number of '%' characters which is the upper > > limit. *scanf functions would not access more arguments than this number. > > Every scanf parameter is pointer, it has fixed size and so upper stack size > > limit can be exactly calculated. > > > > Fix this scanf.S redirect implementation by dynamically allocating stack > > for upper limit of pointer parameters. > > > > --- > > > > I have tested this patch for i686 and x86_64. Both ARM (arm32 and aarch64) > > changes are untested, so please test it if vsscanf() on these platforms > > still works. > > I wonder if we should try to keep the stack 16 byte aligned for i686 too - > GCC generally tries to keep such alignment on i686 too (even if it isn't > strictly required by the ABI). Then again, the only function we call there > is the msvcrt.dll function, which shouldn't assume anything else than 4 byte > alignment, so maybe it's fine.
I do not have any opinion here. If msvc compiler does not align stack to 16 bytes when doing calls to msvcrt.dll functions then I think it is not needed. > I noticed that the arm version that I provided before did crash if providing > less than 2 '%' conversions. I simplified the arm and aarch64 versions a > little and fixed that, see the attached patch that goes on top of this. (I > can squash it locally before pushing the patch too, sparing you a re-send of > the patch, if we decide we don't want to tweak anything else.) It is fine for me. If you have tested it that it works, fell free to squash that your fixup. _______________________________________________ Mingw-w64-public mailing list Mingw-w64-public@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/mingw-w64-public
