On Fri, Jul 25, 2008 at 5:43 PM, Joseph S. Myers <joseph@xxxxxxxxxxxxxxxx> wrote: > On Fri, 25 Jul 2008, Michael Kerrisk wrote: > >> Currently, I'm revising all of the math pages in man-pages, and in the >> process testing the error handling (glibc 2.8) for each function. >> >> I find the following: >> >> a) on error, many (probably a majority of) functions set errno AND >> raise an exception (fetestexcept()). >> b) on error, a very few functions DO set errno but DON"T raise an >> exception (fetestexcept()). >> c) on error, a few functions DON'T set errno but DO raise an exception >> (fetestexcept()). >> d) on error, a very few functions pursue a mixture of all of the >> above, depending on the error. >> >> A math_error(7) page that I recently wrote (see >> http://www.kernel.org/doc/man-pages/online/pages/man7/math_error.7.html >> ) currently implies that all functions should do a). Clearly I'll >> need to amend that. >> >> But the main question is, should I raise glibc bugs for the functions >> in cases b), c), and d)? > > I've run third-party C conformance tests on glibc that have shown similar > issues. > > C90 requires errno to be set by various functions. C99 allows it not to > be set, in an incompatible quiet change from C90, if exceptions are used > instead. The correct handling under C99 depends on the value of > math_errhandling. Implementing math_errhandling requires compiler and > linker support (see messages linked from the CONFORMANCE file): Yes, I saw those already. > if any > translation unit is compiled with -fno-math-errno then math_errhandling & > MATH_ERRNO must not be set. (I'd suggest that the compiler set object > attributes which the static linker then uses to provide the relevant > information to libc.) > > I think the correct approach is to consider it a bug if functions do not > set errno, or do not raise exceptions - that is, all of (b), (c) and (d) > are bugs. This would allow math_errhandling to be > MATH_ERRNO|MATH_ERREXCEPT unless translation units are compiled with > options preventing this, and make the error handling options available > consistent across the math.h functions supported by glibc. To conform > with C99, at least one approach (errno or exceptions) must be consistently > supported across all the functions, in any case. Not even one approach is consistent. Many functions don't set errno. But there are one or two that don't raise exceptions: the Bessel functions (j0(), y0 etc), for example. It's all a bit of a mess, unfortunately. -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ man-pages online: http://www.kernel.org/doc/man-pages/online_pages.html Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
