Am Sonntag, den 09.02.2014, 02:05 -0800 schrieb Andi Kleen: > > EBX is a reserved as the base register when compiling with -fPIC. > > Otherwise it get a "error: can't find a register in class 'BREG' while > > reloading 'asm'". > > In this case you have to dwarf annotate the push/pop > > > > > > Also I if this calls syscall.S:__kernel_vsyscall it clobbers more > > > registers > > > (ecx at least?) and you need to describe that to gcc with a + > > > > Sine ECX is in use as the second parameter it is still marked as > > clobbered. > > No input parameters are not clobbered. > > > I think it should word... As i know a system call will preserve all > > register expect the EAX, which is marked as in and out for this asm() > > directive. > > Yes the syscall does, but the vsyscall stub does not (for the !0x80 case) >
I cross check all kinds of vsyscall and all do save the ECX registers. So IMHO i see no register modification other than EAX, which is declared as the output register in the asm() directive. This following is what i get with objdump -d. ./arch/x86/vdso/vdso32-sysenter.so: __kernel_vsyscall: push %ecx push %edx push %ebp mov %esp,%ebp sysenter nop nop nop nop nop nop nop int $0x80 pop %ebp pop %edx pop %ecx ret ./arch/x86/vdso/vdso32-int80.so: __kernel_vsyscall: int $0x80 ret ./arch/x86/vdso/vdso32-syscall.so: __kernel_vsyscall: push %ebp mov %ecx,%ebp syscall mov $0x2b,%ecx mov %ecx,%ss mov %ebp,%ecx pop %ebp ret BTW, it is not possible to mark an input parameter with +, this can only done for an output parameter. If there is really an issue what i have overseen, a working solution would be to use an other register for the second parameter (ESI or EDI) and add ECX to the clobber list. - Stefani -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
