On 15.02.2010, at 12:10, Rob Landley wrote: > On Sunday 14 February 2010 08:41:00 Alexander Graf wrote: >> Am Sun 14 Feb 2010 09:36:27 AM CET schrieb Rob Landley <r...@landley.net>: >>> On Thursday 11 February 2010 06:32:12 Alexander Graf wrote: >>>> Rob Landley wrote: >>>>> Static binaries that run under the Linux kernel don't run under >>>>> qemu-ppc. For example, the prebuilt busybox binaries here: >>>>> >>>>> http://busybox.net/downloads/binaries/1.16.0/busybox-powerpc >>>>> >>>>> Don't run under qemu-ppc, but runs just fine under qemu-system-ppc >>>>> with the image at: >>>>> >>>>> >>>>> http://impactlinux.com/fwl/downloads/binaries/system-image-powerpc.tar >>>>> .bz 2 >>>>> >>>>> The reason is that the "powerpc spec" that qemu was written to is for >>>>> AIX, not for Linux, and thus the register layout qemu application >>>>> emulation provides for powerpc doesn't match what the kernel is >>>>> actually doing. >>>>> >>>>> For dynamically linked executables, the dynamic linker reorganizes the >>>>> register contents to match the AIX spec from IBM, but statically >>>>> linked binaries get what the kernel provides directly. Thus binaries >>>>> statically linked against uClibc won't run under qemu-ppc, but run >>>>> under qemu-system-ppc just fine. >>>>> >>>>> I tracked down this problem in 2007: >>>>> >>>>> http://landley.net/notes-2007.html#28-03-2007 >>>>> >>>>> And reported it on the list at the time: >>>>> >>>>> http://lists.gnu.org/archive/html/qemu-devel/2007-03/msg00713.html >>>>> http://lists.gnu.org/archive/html/qemu-devel/2007-03/msg00720.html >>>>> http://lists.gnu.org/archive/html/qemu-devel/2007-04/msg00315.html >>>>> >>>>> However, the then-maintainer of powerpc believed nobody else ever had >>>>> the right to touch "her code": >>>>> >>>>> http://lists.gnu.org/archive/html/qemu-devel/2007-04/msg00198.html >>>>> >>>>> And I was unable to convince her that insisting reality change to >>>>> match a spec which wasn't even for the right platform was not a useful >>>>> approach. Thus the binary in the first link still won't run under >>>>> qemu-ppc three years later, despite running fine under a real Linux >>>>> kernel. >>>> >>>> Patches are always welcome. The only thing you might want to make sure >>>> is that dynamically linked binaries also still continue to work :-). >>> >>> Attached. >>> >>> This may help explain the issue: >>> >>> http://sources.redhat.com/ml/libc-alpha/2003-03/msg00272.html >>> >>> It's not a question of dynamically linked Linux binaries. They work >>> just fine >>> with either register layout. The dynamic linker converts the Linux >>> layout to the AIX layout, and is reentrant so it won't do it a second >>> time if it's already been converted. >>> >>> The problem is that BSD wants the AIX layout, and hence this comment >>> in linux- >>> user/elfload.c function init_thread(): >>> >>> /* Note that isn't exactly what regular kernel does >>> * but this is what the ABI wants and is needed to allow >>> * execution of PPC BSD programs. >>> */ >>> >>> I.E. whoever wrote this already knows it's not what the Linux kernel is >>> actually doing, and they're not doing it for Linux, they're doing it for >>> BSD. >>> >>> The fix is probably to add #ifdef CONFIG_BSD around the appropriate chunk >>> of code. Attached is a patch to do that (plus tweaks to make the "you >>> have an unused variable, break the build!" logic shut up about it). >>> >>> (Yes, I tested that a dynamically linked hello world still worked for >>> me.) >> >> I don't see why it would fail. The link above states that for >> statically linked binaries, r1 points to all the variables. For >> dynamically linked ones, you also get pointers in some regs. >> >> So the only case I can imagine that this breaks anything is that >> uClibc requires register state to be 0. > > Yes, r3 (which is the exit code from the "exec" syscall, and thus 0 if it > worked). In the BSD layout, it's argc (which can never be 0). > > http://lists.gnu.org/archive/html/qemu-devel/2007-03/msg00720.html
So what you really want is something like #ifdef CONFIG_LINUX_USER /* exec return value is always 0 */ env->gpr[3] = 0; #endif just after the #endif in your patch. If you had inlined your patch I could've commented it there. Alex
