Why is there no libatomic default implementation using gthr.h?

Sebastian Huber sebastian.huber@embedded-brains.de
Mon Dec 19 09:03:00 GMT 2022


Hello,

I would like to fix the -fprofile-update=atomic implementation so that 
it works on all targets. Currently, it works only on targets with 64-bit 
atomic operations in hardware (and some special cases). I tried to fix 
it like this:

https://gcc.gnu.org/pipermail/gcc-patches/2022-December/608620.html

The problem with this patch is that it falls back to use functions 
provided by libatomic. The libatomic is currently not supported on all 
targets, for example:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77466

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77378

Why is there no libatomic default implementation using gthr.h?

The C++ library already depends on gthr.h and installs the headers in 
"bits/gthr.h" etc. For this the libstdc++-v3 configure/Makefile 
duplicates some logic from libgcc. Why is the gthr.h stuff not installed 
by libgcc itself?

In libatomic, the POSIX implementation could be easily rewritten to use 
the gthr interface.

Any objections to do the following?

1. Install gthr.h to "bits/gthr.h" by libgcc (including the other gthr 
headers).

2. Remove the gthr configure/Makefile support from libstdc++-v3.

3. Use gthr as the default implementation of libatomic.

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