asm impossible constraint

[juliandroid]

I get the following error, while running:

$ make
...
make[4]: Entering directory '/home/july/msed/syslinux/gpxe/src' [BUILD] bin/int13.o arch/i386/interface/pcbios/int13.c: In function ‘register_int13_drive’: arch/i386/interface/pcbios/int13.c:469:2: warning: asm operand 0 probably doesn’t match constraints __asm__ __volatile__ ( ^ arch/i386/interface/pcbios/int13.c:469:2: error: impossible constraint in ‘asm’ bin/deps/arch/i386/interface/pcbios/int13.c.d:86: recipe for target 'bin/int13.o' failed make[4]: *** [bin/int13.o] Error 1

My build env is:
$ nasm -v
NASM version 2.11.08 compiled on Mar 24 2015

$ gcc -v
Using built-in specs.

COLLECT_GCC=/usr/bin/gcc

COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-unknown-linux-gnu/5.3.0/lto-wrapper

Target: x86_64-unknown-linux-gnu

Configured with: /build/gcc-multilib/src/gcc-5.3.0/configure --prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/ --enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-shared --enable-threads=posix --enable-libmpx --with-system-zlib --with-isl --enable-__cxa_atexit --disable-libunwind-exceptions --enable-clocale=gnu --disable-libstdcxx-pch --disable-libssp --enable-gnu-unique-object --enable-linker-build-id --enable-lto --enable-plugin --enable-install-libiberty --with-linker-hash-style=gnu --enable-gnu-indirect-function --enable-multilib --disable-werror --enable-checking=release

Thread model: posix

gcc version 5.3.0 (GCC)

$ make -v

GNU Make 4.1

Built for x86_64-unknown-linux-gnu

$ uname -a

Linux stoffle 4.3.3-3-ARCH #1 SMP PREEMPT Wed Jan 20 08:12:23 CET 2016 x86_64 GNU/Linux

I'm running Arch Linux, so all the tools are the latest versions of respective tools.

I'm not an expert of asm constraints, but I did a couple of changes in order to complete the make process (see the patch file). I assume, those changes might be wrong (EDIT: are wrong - see my next comment).
asm_constraints.patch.zip

Regards,
Julian

[juliandroid]

Ok, I figured it out.
The gcc 5.3.0 (in Arch Linux at least) by default builds position-independent code.
The fix for my gcc is:

diff --git gpxe/src/Makefile.housekeeping gpxe/src/Makefile.housekeeping
index 1f5e115..296ebcf 100644
--- gpxe/src/Makefile.housekeeping
+++ gpxe/src/Makefile.housekeeping
@@ -337,6 +337,7 @@ CFLAGS              += -g
 ifeq ($(CCTYPE),gcc)
 CFLAGS         += -ffreestanding
 CFLAGS         += -Wall -W -Wformat-nonliteral
+CFLAGS         += -fno-PIE
 endif
 ifeq ($(CCTYPE),icc)
 CFLAGS         += -fno-builtin

The gcc compiler should be tested for -fno-PIE option and if it does support it then should be passed as an extra CFLAG option.

[r0m30]

That is an upstream change to the syslinux code base that is used for the biospba. I haven't looked at the sysllinux repo in a while so it may already be there. It might be a good thing to send this to them they are at www.syslinux.org.

[juliandroid]

Yes, I did that.

My suggestion is to fix the Makefile with code that looks something like that:

diff --git gpxe/src/arch/i386/Makefile gpxe/src/arch/i386/Makefile
index dd8da80..5133bd9 100644
--- gpxe/src/arch/i386/Makefile
+++ gpxe/src/arch/i386/Makefile
@@ -67,6 +67,10 @@ CFLAGS       += -fshort-wchar
 #
 CFLAGS         += -Ui386

+GCC_HAS_NO_PIE = [ -z "`$(CC) -fno-PIE -x c -c /dev/null -o /dev/null 2>&1`" ]
+NO_PIE_FLAG := $(shell $(GCC_HAS_NO_PIE) && $(ECHO) '-fno-PIE')
+CFLAGS += $(NO_PIE_FLAG)
+
 # Locations of utilities
 #
 ISOLINUX_BIN   = /usr/lib/syslinux/isolinux.bin

I'm attaching my patch here in case someone else face the same hurdle while building syslinux. Be aware this patch is for their git repository not for this one - i.e. the patch may need to be applied manually.

[r0m30]

Great, thanks.

[LITTENg]

@juliandroid Great thanks, this patch really help me a lot.