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Use DWARF unwinding with Clang to avoid overproduction of linking warnings with clang + gfortran #18

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Use DWARF unwinding with Clang to avoid overproduction of linking warnings with clang + gfortran #18

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fef6cae
Use DWARF unwinding with Clang to avoid overproduction of linking
GiudGiud Jan 13, 2025
ac33154
Add a linking test before adding linking flags to disable compact unw…
GiudGiud Jan 30, 2025
a5196d0
Fix linking test
GiudGiud Jan 31, 2025
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18 changes: 18 additions & 0 deletions acsm_compiler_flags.m4
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Original file line number Diff line number Diff line change
Expand Up @@ -585,6 +585,24 @@ AC_DEFUN([ACSM_SET_CXX_FLAGS],
],

[clang], [
dnl On Darwin with clang + gfortran, we get very many warnings for compact unwinding issues
dnl We deliberately keep relying on the less performant dwarf unwinding until the over-production of warnings is solved.
OLD_ACSM_LDFLAGS="$ACSM_LDFLAGS"
ACSM_LDFLAGS+=" -Wl,-femit-dwarf-unwind=no_compact_unwind"
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As I understand it, AC_LINK_IFELSE specifically uses the variables LIBS and LDFLAGS to test linking:

https://www.gnu.org/software/autoconf/manual/autoconf-2.69/html_node/Running-the-Linker.html

So I think you need to do like in the xdr example, and set the LIBS variable prior to calling AC_LINK_IFELSE. Also, it seems to me that there is an issue with your test program, it will need to #include <iostream> in order to be well-formed.

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ok I changed it

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"-femit-dwarf-unwind=always" does not do much here btw, it s the two others that make the warnings disappear

AC_LINK_IFELSE([AC_LANG_SOURCE([[
void main(int argc, char **argv)
{
std::cout << "Hello World!" << std::endl;
}
]])],
[
AC_MSG_RESULT(<<<Disabling compact unwinding, retaining dwarf unwinding for gfortran compatibility>>>)
],[
dnl Failed to link with new flags, remove them
ACSM_LDFLAGS="$OLD_ACSM_LDFLAGS"
])


ACSM_CXXFLAGS_OPT="$ACSM_CXXFLAGS_OPT -O2 -felide-constructors -Qunused-arguments -Wunused-parameter -Wunused"
dnl devel flags are added on two lines since there are so many
ACSM_CXXFLAGS_DEVEL="$ACSM_CXXFLAGS_DEVEL -O2 -felide-constructors -g -pedantic -W -Wall -Wextra -Wno-long-long"
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