The cross-platform version of gcc ignore the attribute tag attribute((interrupt)) of my function

Question

I downloaded the intel IA-64 and 32 book because I wanted to know more in depth about how a CPU works. So I read the book and started to code some stuff. I enabled the IDT and when I want to program an interrupt handler I have that code :

extern "C"  __attribute__((interrupt)) void test (void* ptr)
{

}

int main (void)
{
    return 0;
}

when I compile with i686-elf-g++ -Wall -Wextra -O2 -c -m32 main.cpp I have the following warning : main.cpp:6:60: warning: 'interrupt' attribute directive ignored, but when I compile with g++ -Wall -Wextra -O2 -c -m32 main.cpp the compilation just works well and the code generated is like it should be with the iret instruction at the end (and that's what I want) :

Disassembly of section __TEXT,__text:
_test:
       0:       55      push    ebp
       1:       89 e5   mov     ebp, esp
       3:       fc      cld
       4:       5d      pop     ebp
       5:       cf      iretd
       6:       66 2e 0f 1f 84 00 00 00 00 00   nop     word ptr cs:[eax + eax]

Does anyone have any idea of why I have this warning with my cross platform version of gcc ? (and I am also wondering why an interrupt handler must have a pointer at parameter for gcc)

Are you on Windows with your "regular" g++ set up to build Windows object files? I was confused at first because you don't need a special i686 version of gcc to make 32-bit x86 code. — Peter Cordes
– Peter Cordes, Commented Oct 30, 2017 at 4:58
@PeterCordes I am on macOS and my g++ is clang++ 9.0.0. To tell the truth, when I started I had no idea of what I was doing, so I just followed the tutoriel on OSDev link . But I guess that if I doesn't set a prefix value to null gcc set its value to the targeted architecture (and in my case it was i686- and the elf is because of the tutoriel but maybe I don't need that) — Adrien
– Adrien, Commented Oct 30, 2017 at 8:29
@PeterCordes : I assumed from the question (using interrupt directive) that h'es doing OS development and using a cross compiler (which is recommended on OSDev wiki since the old days some distros use to tie/patch libgcc to use some host OS features). As well, on OS/X LD doesn't support many of the options needed (like linker scripts) that allow you to OS Dev (So GNU Binutils is also much handier). — Michael Petch
– Michael Petch, Commented Oct 30, 2017 at 13:33
@MichaelPetch you're right even if I wouldn't have the pretension of saying that I am developing an OS ^^ I am just trying to put the CPU in a usable mode, but I will be pretty happy if this little project could ends up in an nice working OS — Adrien
– Adrien, Commented Oct 30, 2017 at 22:09

Michael Petch · Accepted Answer · 2017-10-29 23:13:17Z

4

The interrupt attribute is only a recent addition to G++ when targeting x86/x86-64 architectures and is available in G++ 7.0 and later.I would guess that your i686-elf-g++ cross compiler is earlier than 7.0 and your host compiler g++ is 7.0 or later. You'll have to upgrade your i686 cross compiler to a newer version.

edited Oct 29, 2017 at 23:13

answered Oct 29, 2017 at 22:48

Michael Petch

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6 Comments

Adrien Over a year ago

Really ? My regular version of g++ is clang++ 9.0.0 (I am on macOS) and my i686-elf-g++ version is 6.3.0. I founded the interrupt attribute when searching in the 6.3.0 documentation of g++ it is a little bit weird to document a feature that is not present oO

Michael Petch Over a year ago

Apple's Clang/LLVM seems to have only supported the interrupt attribute since version 9 when targeting x86/x86-64. It has supported the interrupt attribute on functions for other targets like ARM and MIPS for much longer.

Michael Petch Over a year ago

@Adrien : GCC and CLANG are different projects. And Apple has its own version of CLANG/LLVM with later XCode releases. The interrupt attribute has been around a while but only properly implemented for architectures like ARM and MIPS. It has been only more recently in GCC/CLANG/Apple CLANG(since about 2016). for the x86 and x86-64 platforms.

Michael Petch Over a year ago

Older versions would ignore the interrupt attribute and usually throw a warning on unsupported platforms and it would be ignored.

Adrien Over a year ago

Thanks it works well with gcc 7+, but I remember an advice saying that I should not use the last release but a one a little bit older because the newest are not tested enough, so maybe I should find another way to program interrupt handler in C/C++ ?

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