On Wed, Jan 24, 2024 at 11:13:05AM +0200, Janne Blomqvist wrote: > On Wed, Jan 24, 2024 at 10:28 AM FX Coudert <fxcoud...@gmail.com> wrote: > > > Now, if > > > the OS adds cospi() to libm and it's in libm's symbol map, then the > > > cospi() used by gfortran depends on the search order of the loaded > > > libraries. > > > > We only include the fallback math functions in libgfortran when they are > > not available on the system. configure detects what is present in the libc > > being targeted, and conditionally compiles the necessary fallback functions > > (and only them). > > Exactly. However, there is the (corner?) case when libgfortran has > been compiled, and cospi() not found and thus the fallback > implementation is included, and then later libc is updated to a > version that does provide cospi(). I believe in that case which > version gets used is down to the library search order (i.e. the order > that "ldd /path/to/binary" prints the libs), it will use the first > symbol it finds. Also, it's not necessary to do some ifdef tricks > with gfortran.map, if a symbol listed there isn't found in the library > it's just ignored. So the *pi() trig functions can be unconditionally > added there, and then depending on whether the target libm includes > those or not they are then included in the exported symbol list. > > It's possible to override this to look for specific symbol versions > etc., but that probably goes deep into the weeds of target-specific > stuff (e.g. are we looking for cospi@FBSD_1.7, cospi@GLIBC_X.Y.Z, or > something else?). I'm sure you don't wanna go there. >
Ah, so that's the part I was missing. I was under the impression that if a symbol appears in a libraries symbol map, then the library had to contain a function by that name. If the loader ignores symbols for a missing function, then yes, I think I can get rid of the indirection via _gfortran_cospi_r4(). It will take a few days for me to redesign this, which shouldn't be too problematic in that GCC is in stage 4 and this is neither a regression or doc fix. Janne, FX, Harald, thanks for taking a peek. -- Steve
