Messages in this thread | | | Date | Wed, 12 Nov 2008 13:33:36 +0100 | From | Mikael Pettersson <> | Subject | Re: [PATCH 2/2] x86: ia32_signal: remove unnecessary padding |
| |
Ingo Molnar writes: > > * Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com> wrote: > > > From: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com> > > > > Impact: cleanup > > > > Remove unnecessary paddings, this saves 4 bytes. > > > > Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com> > > --- > > arch/x86/ia32/ia32_signal.c | 5 +---- > > 1 files changed, 1 insertions(+), 4 deletions(-) > > applied your patches to tip/x86/signal: > > 9cc3c49: x86: ia32_signal: remove unnecessary padding > 4a61204: x86: signal_32: introduce retcode and rt_retcode > > thanks! > > A question - this change: > > > @@ -427,12 +427,10 @@ int ia32_setup_frame(int sig, struct k_sigaction *ka, > > u16 poplmovl; > > u32 val; > > u16 int80; > > - u16 pad; > > } __attribute__((packed)) code = { > > 0xb858, /* popl %eax ; movl $...,%eax */ > > __NR_ia32_sigreturn, > > 0x80cd, /* int $0x80 */ > > - 0, > > }; > > > > frame = get_sigframe(ka, regs, sizeof(*frame), &fpstate); > > @@ -508,8 +506,7 @@ int ia32_setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info, > > u8 movl; > > u32 val; > > u16 int80; > > - u16 pad; > > - u8 pad2; > > + u8 pad; > > } __attribute__((packed)) code = { > > 0xb8, > > __NR_ia32_rt_sigreturn, > > does not impact any ABI, because it's only about the signal trampoline > the kernel pushes to the user-space stack - not about any > userspace-visible signal frame detail, right?
As long as the 'char retcode[8]' field isn't reduced in size (you can _never_ do that!), and the initial instruction sequence up to the 'int $0x80' isn't changed (you can't change that either), I believe this is safe.
It does cause each signal delivery to leak 2 uninitialised kernel bytes to the end of retcode[], which seems unnecessary.
| |