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Re: [PATCH v3] Change default to -fno-math-errno


On Thu, 11 Oct 2018, Wilco Dijkstra wrote:

> For the new math functions all errno handling is already done in a 
> single function so you could do something like: if (want_errno) 
> set_errno (error).

want_errno being a global (or TLS) variable gets into the same problems as 
_LIB_VERSION; you want something that's a property of the particular call 
to the function, based on the options used to compile that call (which 
gets you into either wrappers, or building selected functions twice to 
provide no-errno-setting entry point, if you want to be able to optimize 
on the basis that a call cannot change errno).

Saving and restoring seems a plausible approach if you want to e.g. 
provide a guarantee in future glibc versions that complex.h functions will 
not set errno (they'd need review to see if at present they can actually 
call any error cases of other functions that might set errno, or if there 
isn't a problem anyway).

-- 
Joseph S. Myers
joseph@codesourcery.com


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