gcc -O2 vs. without causes error

Question

When compiling file containing open("FILENAME", O_RDONLY); without -O2 flag everything is fine. But when -O2 is turned on I get:

/usr/include/x86_64-linux-gnu/bits/fcntl2.h: In function ‘open’:
/usr/include/x86_64-linux-gnu/bits/fcntl2.h:44:7: error: invalid use of ‘__builtin_va_arg_pack_len ()’
/usr/include/x86_64-linux-gnu/bits/fcntl2.h:45:26: error: call to ‘__open_too_many_args’ declared with attribute error: open can be called either with 2 or 3 arguments, not more
/usr/include/x86_64-linux-gnu/bits/fcntl2.h:42:1: error: invalid use of ‘__builtin_va_arg_pack_len ()’
/usr/include/x86_64-linux-gnu/bits/fcntl2.h:60:3: error: invalid use of ‘__builtin_va_arg_pack ()’
/usr/include/x86_64-linux-gnu/bits/fcntl2.h: In function ‘open64’:
/usr/include/x86_64-linux-gnu/bits/fcntl2.h:76:7: error: invalid use of ‘__builtin_va_arg_pack_len ()’
/usr/include/x86_64-linux-gnu/bits/fcntl2.h:77:28: error: call to ‘__open64_too_many_args’ declared with attribute error: open64 can be called either with 2 or 3 arguments, not more
/usr/include/x86_64-linux-gnu/bits/fcntl2.h:74:1: error: invalid use of ‘__builtin_va_arg_pack_len ()’
/usr/include/x86_64-linux-gnu/bits/fcntl2.h:92:3: error: invalid use of ‘__builtin_va_arg_pack ()’
/usr/include/x86_64-linux-gnu/bits/fcntl2.h: In function ‘openat’:
/usr/include/x86_64-linux-gnu/bits/fcntl2.h:120:7: error: invalid use of ‘__builtin_va_arg_pack_len ()’
/usr/include/x86_64-linux-gnu/bits/fcntl2.h:121:28: error: call to ‘__openat_too_many_args’ declared with attribute error: openat can be called either with 3 or 4 arguments, not more
/usr/include/x86_64-linux-gnu/bits/fcntl2.h:118:1: error: invalid use of ‘__builtin_va_arg_pack_len ()’
/usr/include/x86_64-linux-gnu/bits/fcntl2.h:136:3: error: invalid use of ‘__builtin_va_arg_pack ()’
/usr/include/x86_64-linux-gnu/bits/fcntl2.h: In function ‘openat64’:
/usr/include/x86_64-linux-gnu/bits/fcntl2.h:154:7: error: invalid use of ‘__builtin_va_arg_pack_len ()’
/usr/include/x86_64-linux-gnu/bits/fcntl2.h:155:30: error: call to ‘__openat64_too_many_args’ declared with attribute error: openat64 can be called either with 3 or 4 arguments, not more
/usr/include/x86_64-linux-gnu/bits/fcntl2.h:152:1: error: invalid use of ‘__builtin_va_arg_pack_len ()’
/usr/include/x86_64-linux-gnu/bits/fcntl2.h:170:3: error: invalid use of ‘__builtin_va_arg_pack ()’

Where can be the problem? It's mixed C/C++ project but this is in the C part. gcc 4.6.1, kernel 3.0.0

Edit: It turns out that commeting out those line gives another "type" of errors like:

/usr/include/x86_64-linux-gnu/bits/stdio2.h: In function ‘sprintf’:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:34:3: error: invalid use of ‘__builtin_va_arg_pack ()’

Answer 1

I hit this when trying to compile https://www.spec.org/cpu2017/Docs/benchmarks/602.gcc_s.html with GCC.

Ironically, the bootstrap process would fail due to GCC apparently not understanding GNU extensions.

Turning on -fgnu89-inline got rid of any problems I was having. Alternatively, use -std=gnu89.