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Date: Wed, 27 Jan 2016 17:57:28 +0100
From: Marc =?UTF-8?B?TWFyw60=?= <markmb@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v3] Add optionrom compatible with fw_cfg
	DMA version
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To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: "Gabriel L. Somlo" <somlo@cmu.edu>, qemu-devel@nongnu.org, Kevin O'Connor <kevin@koconnor.net>, Gerd Hoffmann <kraxel@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Laszlo <lersek@redhat.com>

On Wed, 27 Jan 2016 16:43:29 +0000
Stefan Hajnoczi <stefanha@redhat.com> wrote:

> On Tue, Jan 26, 2016 at 12:26:12PM +0100, Gerd Hoffmann wrote:
> > On Di, 2016-01-26 at 12:20 +0100, Marc Mar=C3=AD wrote: =20
> > > On Tue, 26 Jan 2016 11:11:54 +0000
> > > Stefan Hajnoczi <stefanha@redhat.com> wrote:
> > >  =20
> > > > On Mon, Jan 25, 2016 at 02:17:48PM +0100, Marc Mar=C3=AD wrote: =20
> > > > > +linuxboot_dma.img: linuxboot_dma.o
> > > > > +	$(call quiet-command,$(LD) $(LDFLAGS_NOPIE) -m
> > > > > elf_i386 -Ttext 0 -e _start -s -o $@ $<,"  Building
> > > > > $(TARGET_DIR)$@") + %.img: %.o
> > > > >  	$(call quiet-command,$(LD) $(LDFLAGS_NOPIE) -Ttext 0
> > > > > -e _start -s -o $@ $<,"  Building $(TARGET_DIR)$@")   =20
> > > >=20
> > > > Why is -m elf_i386 necessary for linuxboot_dma.img but not for
> > > > the other *.img files? =20
> > >=20
> > > I cannot give a precise explanation. But if I don't force an
> > > output type, I get this error:
> > >=20
> > > Building optionrom/linuxboot_dma.img
> > > ld: i386 architecture of input file `linuxboot_dma.o' is
> > > incompatible with i386:x86-64 output =20
> >=20
> > Any chance the linker needs -m32 too? =20
>=20
> I wonder why this isn't a problem for the existing firmware code.  Are
> we really building x86_64 ELF files for our firmware?

Yes they are x86_64:

pc-bios/optionrom/linuxboot.img: ELF 64-bit LSB executable, x86-64,
version 1 (SYSV), statically linked, stripped

But as they are written directly in assembly, it does not give any
problem. Whereas when mixing C and ASM, it does give problems.

Marc