https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103570
Bug ID: 103570
Summary: Libstdc++ fails to build with compilers that already
have a C++ library on their path
Product: gcc
Version: 11.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: pedro.falcato at gmail dot com
Target Milestone: ---
Created attachment 51930
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51930&action=edit
GCC Error log with -H
GCC 11.2.0's libstdc++ fails to build when trying to build it with a compiler
that already contains C++ headers on its path. Because of this, the build fails
when cross-compiling GCC itself to another system (which doesn't use the newly
built GCC, because it can't).
Simplifying the test, I managed to reproduce it fairly reliably with simply:
../gcc-11.2.0/libstdc++/configure && make
I hit this error using --host=aarch64-linux-gnu
Eventually, it will fail on:
aarch64-linux-gnu-g++
-I/home/pfalcato/armstuff/gcc-11.2.0/libstdc++-v3/../libgcc
-I/home/pfalcato/armstuff/gcc-build/include/aarch64-linux-gnu
-I/home/pfalcato/armstuff/gcc-build/include
-I/home/pfalcato/armstuff/gcc-11.2.0/libstdc++-v3/libsupc++ -std=gnu++17
-D_GLIBCXX_SHARED -fno-implicit-templates -Wall -Wextra -Wwrite-strings
-Wcast-qual -Wabi=2 -fdiagnostics-show-location=once -ffunction-sections
-fdata-sections -frandom-seed=floating_from_chars.lo -fimplicit-templates -c
../../../gcc-11.2.0/libstdc++-v3/src/c++17/floating_from_chars.cc -fPIC -DPIC
-D_GLIBCXX_SHARED -o floating_from_chars.o
Running libstdc++'s configure without any host hits a similar error.
Attached is a detailed log of the compile command, with -H appended on it for
clarity's sake.
By looking at -H's output, we can deduce that in-tree libstdc++ fenv.h
includes_next the compiler's fenv.h, which fails to include_next libc's fenv.h
due to the in-tree's fenv.h and the compiler's fenv.h headers guards being the
same.
