fpu_control.h: Potentially using wrong include paths when building older glibc with newer cross-compiler

[Ahmad Bamba]

Hello all,

I'm trying to build a cross-compiler (x86_64-pc-linux-gnu ->
mips64octeon-linux), and in doing so I'm trying to build glibc. I get the
following error in the middle of building glibc 2.16.0 with the
recently-built cross compiler while building -lm:
   make[2]: Entering directory `/media/glibc-2.16.0/math'
   /opt/cross/bin/mips64octeon-linux-gcc -mabi=n32
../sysdeps/mips/fpu/feholdexcpt.c -c -std=gnu99 -fgnu89-inline  -O2 -Wall
-Winline -Wwrite-strings -fmerge-all-constants -frounding-math -g
-Wstrict-prototypes      -Wno-uninitialized  -mabi=n32 -D__NO_MATH_INLINES
-D__LIBC_INTERNAL_MATH_INLINES -I../include -I/objdir-glibc/math
-I/objdir-glibc -I../sysdeps/unix/sysv/linux/mips/mips64/n32/nptl
-I../sysdeps/unix/sysv/linux/mips/mips64/n32
-I../sysdeps/unix/sysv/linux/mips/mips64/nptl
-I../sysdeps/unix/sysv/linux/mips/mips64
-I../sysdeps/unix/sysv/linux/mips/nptl -I../sysdeps/unix/sysv/linux/mips
-I../nptl/sysdeps/unix/sysv/linux -I../nptl/sysdeps/pthread
-I../sysdeps/pthread -I../sysdeps/unix/sysv/linux -I../sysdeps/gnu
-I../sysdeps/unix/inet -I../nptl/sysdeps/unix/sysv -I../sysdeps/unix/sysv
-I../sysdeps/unix/mips/mips64/n32 -I../sysdeps/unix/mips/mips64
-I../sysdeps/unix/mips -I../nptl/sysdeps/unix -I../sysdeps/unix
-I../sysdeps/posix -I../sysdeps/mips/mips64/n32
-I../sysdeps/ieee754/ldbl-128 -I../sysdeps/mips/mips64/soft-fp
-I../sysdeps/mips/mips64 -I../sysdeps/ieee754/flt-32
-I../sysdeps/ieee754/dbl-64 -I../sysdeps/mips -I../sysdeps/wordsize-32
-I../sysdeps/mips/fpu -I../sysdeps/mips/nptl -I../sysdeps/ieee754
-I../sysdeps/generic -I../nptl  -I.. -I../libio -I. -nostdinc -isystem
/opt/cross/lib/gcc/mips64octeon-linux/13.3.1/include -isystem
/opt/cross/lib/gcc/mips64octeon-linux/13.3.1/include-fixed -isystem
/opt/cross/mips64octeon-linux/include/ -D_LIBC_REENTRANT -include
../include/libc-symbols.h  -DPIC -DNOT_IN_libc=1 -DIS_IN_libm=1
-DIN_LIB=libm    -I../soft-fp -o /objdir-glibc/math/feholdexcpt.o -MD -MP
-MF /objdir-glibc/math/feholdexcpt.o.dt -MT
/objdir-glibc/math/feholdexcpt.o
   In file included from ../include/fpu_control.h:1,
                  from ../sysdeps/mips/fpu/feholdexcpt.c:21:
   ../sysdeps/mips/fpu/feholdexcpt.c: In function ‘feholdexcept’:
   ../sysdeps/mips/fpu_control.h:66:24: warning: statement with no effect
[-Wunused-value]
      66 | #define _FPU_GETCW(cw) 0
         |                        ^
   ../sysdeps/mips/fpu/feholdexcpt.c:29:3: note: in expansion of macro
‘_FPU_GETCW’
      29 |   _FPU_GETCW (cw);
         |   ^~~~~~~~~~
   ../sysdeps/mips/fpu/feholdexcpt.c:33:11: error: ‘_FPU_MASK_V’ undeclared
(first use in this function)
      33 |   cw &=
~(_FPU_MASK_V|_FPU_MASK_Z|_FPU_MASK_O|_FPU_MASK_U|_FPU_MASK_I|FE_ALL_EXCEPT);
         |           ^~~~~~~~~~~
   ../sysdeps/mips/fpu/feholdexcpt.c:33:11: note: each undeclared
identifier is reported only once for each function it appears in
   ../sysdeps/mips/fpu/feholdexcpt.c:33:23: error: ‘_FPU_MASK_Z’ undeclared
(first use in this function)
      33 |   cw &=
~(_FPU_MASK_V|_FPU_MASK_Z|_FPU_MASK_O|_FPU_MASK_U|_FPU_MASK_I|FE_ALL_EXCEPT);
         |                       ^~~~~~~~~~~
   ../sysdeps/mips/fpu/feholdexcpt.c:33:35: error: ‘_FPU_MASK_O’ undeclared
(first use in this function)
      33 |   cw &=
~(_FPU_MASK_V|_FPU_MASK_Z|_FPU_MASK_O|_FPU_MASK_U|_FPU_MASK_I|FE_ALL_EXCEPT);
         |                                   ^~~~~~~~~~~
   ../sysdeps/mips/fpu/feholdexcpt.c:33:47: error: ‘_FPU_MASK_U’ undeclared
(first use in this function)
      33 |   cw &=
~(_FPU_MASK_V|_FPU_MASK_Z|_FPU_MASK_O|_FPU_MASK_U|_FPU_MASK_I|FE_ALL_EXCEPT);
         |                                               ^~~~~~~~~~~
   ../sysdeps/mips/fpu/feholdexcpt.c:33:59: error: ‘_FPU_MASK_I’ undeclared
(first use in this function)
      33 |   cw &=
~(_FPU_MASK_V|_FPU_MASK_Z|_FPU_MASK_O|_FPU_MASK_U|_FPU_MASK_I|FE_ALL_EXCEPT);
         |
^~~~~~~~~~~
   make[2]: *** [/objdir-glibc/math/feholdexcpt.o] Error 1
   make[2]: Leaving directory `/media/glibc-2.16.0/math'
   make[1]: *** [math/others] Error 2
   make[1]: Leaving directory `/media/glibc-2.16.0'
   make: *** [all] Error 2

Cross compiler information is as follows:
   [root@7b1d394705f7 objdir-glibc]# /opt/cross/bin/mips64octeon-linux-gcc
--version
   mips64octeon-linux-gcc (GCC) 13.3.1 20240817
   Copyright (C) 2023 Free Software Foundation, Inc.
   This is free software; see the source for copying conditions.  There is
NO
   warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE.

These _FPU_MASK macros seem to be defined in sysdeps/mips/fpu_control.h,
which is in the the include path of the posted command. This tells me that
the build may be getting to the system header first, located at
/usr/include/fpu_control.h. But I'm super new to this and I'm not sure how
to get gcc to ignore /usr/include, or consider it after it has considered
these other include directories? The nostdinc flag is passed by default so
I'm not sure what else to do.

This was my configure command:
    CC=/opt/cross/bin/mips64octeon-linux-gcc
CXX=/opt/cross/bin/mips64octeon-linux-g++ /media/glibc-2.16.0/configure
--prefix=/opt/cross/mips64octeon-linux/ --build=$MACHTYPE
--host=mips64octeon-linux
--with-headers=/opt/cross/mips64octeon-linux/include/ --disable-multilib
libc_cv_forced_unwind=yes

Unfortunately, the octeon device I am targeting has an old glibc and linux
kernel version on it. For the purposes of this question, let's assume
there's no way to update it or statically link glibc in my binaries.

Thanks in advance,
Ahmad