[ipxe-devel] iPXE build failure on Fedora 19 (rawhide)

[Daniel P. Berrange]

On Tue, Mar 05, 2013 at 01:48:29PM +0000, Michael Brown wrote:
> On 22/02/13 15:40, Daniel P. Berrange wrote:
> >Building on Fedora 19 rawhide, which has latest gcc 4.8.0 I'm seeing the
> >following failure on the pxe_call.c file:
> >
> >   gcc  -DARCH=i386 -DPLATFORM=pcbios -march=i386 -fomit-frame-pointer -fstrength-reduce -falign-jumps=1 -falign-loops=1 -falign-functions=1 -mpreferred-stack-boundary=2 -mregparm=3 -mrtd -freg-struct-return -m32 -fshort-wchar -Ui386 -Ulinux -DNVALGRIND -Iinclude -I. -Iarch/x86/include -Iarch/i386/include -Iarch/i386/include/pcbios -Os -g -ffreestanding -Wall -W -Wformat-nonliteral   -fno-stack-protector  -fno-dwarf2-cfi-asm -fno-exceptions  -fno-unwind-tables -fno-asynchronous-unwind-tables -Wno-address  -ffunction-sections -fdata-sections -include compiler.h   -DOBJECT=pxe_call -c arch/i386/interface/pxe/pxe_call.c -o bin/pxe_call.o
> >   arch/i386/interface/pxe/pxe_call.c: In function 'pxe_start_nbp':
> >   arch/i386/interface/pxe/pxe_call.c:284:1: error: bp cannot be used in asm here
> >    }
> >    ^
> >   make: *** [bin/pxe_call.o] Error 1
> >
> ><snip>
> >
> >asm isn't my strong field, so anyone know if this is a valid ipxe bug, or
> >a mistaken report from newest gcc ?
> 
> gcc has a history of interesting failures relating to using the
> frame pointer in inline asm; see e.g
> 
>   http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11807
>   http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28686
> 
> We've had to work around this kind of problem before:
> 
>   http://git.ipxe.org/ipxe.git/commitdiff/54fbd11
> 
> The quickest hack to fix this would be to manually preserve ebp via
> a pushl/popl within the inline asm, as is currently done in
> meme820() and multiboot_exec().  However, this is an ugly fix, not
> least because it makes it impossible to refer to local variables in
> asm constraints. Slightly neater would be to explicitly specify ebp
> as an unused output operand, but it's possible gcc would then
> complain about "impossible constraints in asm".
> 
> I've applied for access to the GCC Compile Farm, to make it easier
> to try out various fixes across multiple gcc versions.  In the
> meantime, if anyone has a gcc 4.8.0 box already set up and wants to
> report on whether or not the unused-output approach works, please do
> so!

If you can provide the possible patch, I'll happily give it a spin on
a Fedora rawhide gcc 4.8.

Daniel
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