Messages in this thread | | | Subject | Re: [PATCH v13 8/9] Add 32 bit VDSO time support for 32 bit kernel | From | Stefani Seibold <> | Date | Sun, 09 Feb 2014 12:45:17 +0100 |
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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
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