Hi,
On Thu, Jan 26, 2012 at 07:03:43PM +0100, Denys Vlasenko wrote:
> Hi Linus,
>
> On Thu, Jan 26, 2012 at 4:47 AM, Linus Torvalds
> <[email protected]> wrote:
> >> Please look at strace source, get_scno() function, where
> >> it reads syscall no and parameters. Let's see....
> >> - POWERPC: has 32-bit and 64-bit mode
> >> - X86_64: has 32-bit and 64-bit mode
> >> - IA64: has i386-compat mode
> >> - ARM: has more than one ABI
> >> - SPARC: has 32-bit and 64-bit mode
> >>
> >> Do you want to re-invent a different arch-specific way to report
> >> syscall type for each of these arches?
> >
> > I think an arch-specific one is better than trying to make some
> > generic one that is messy.
> >
> > As you say, many architectures have multiple system call ABIs.
> >
> > But they tend to be very *different* issues. They can be about
> > multiple ABI's, as you mention, and even when they *look* similar
> > (32-bit vs 64-bit ABI's) they are actually totally different issues.
> > [skip]
>
> I don't have a particular attachment to my solution,
> and I think we already talk about this problem for
> far too long.
>
> Looks like nobody is _strongly_ opposed to your patch
> which uses a few bits in eflags to report bitness
> of the x86 syscall.
>
> Lets just do that already. If you commit it to kernel git,
> I will immediately change strace accordingly.
Is there any progress with this (or any alternative) solution?
I see the kernel side has changed a bit, and the strace part
is in a better shape than 5 years ago (although I'm biased of course),
but I don't see any kernel interface that would allow strace to reliably
recognize this 0x80 case.
--
ldv
On Wed, Mar 8, 2017 at 3:41 PM, Dmitry V. Levin <[email protected]> wrote:
> Hi,
>
> On Thu, Jan 26, 2012 at 07:03:43PM +0100, Denys Vlasenko wrote:
>> Hi Linus,
>>
>> On Thu, Jan 26, 2012 at 4:47 AM, Linus Torvalds
>> <[email protected]> wrote:
>> >> Please look at strace source, get_scno() function, where
>> >> it reads syscall no and parameters. Let's see....
>> >> - POWERPC: has 32-bit and 64-bit mode
>> >> - X86_64: has 32-bit and 64-bit mode
>> >> - IA64: has i386-compat mode
>> >> - ARM: has more than one ABI
>> >> - SPARC: has 32-bit and 64-bit mode
>> >>
>> >> Do you want to re-invent a different arch-specific way to report
>> >> syscall type for each of these arches?
>> >
>> > I think an arch-specific one is better than trying to make some
>> > generic one that is messy.
>> >
>> > As you say, many architectures have multiple system call ABIs.
>> >
>> > But they tend to be very *different* issues. They can be about
>> > multiple ABI's, as you mention, and even when they *look* similar
>> > (32-bit vs 64-bit ABI's) they are actually totally different issues.
>> > [skip]
>>
>> I don't have a particular attachment to my solution,
>> and I think we already talk about this problem for
>> far too long.
>>
>> Looks like nobody is _strongly_ opposed to your patch
>> which uses a few bits in eflags to report bitness
>> of the x86 syscall.
>>
>> Lets just do that already. If you commit it to kernel git,
>> I will immediately change strace accordingly.
>
> Is there any progress with this (or any alternative) solution?
>
> I see the kernel side has changed a bit, and the strace part
> is in a better shape than 5 years ago (although I'm biased of course),
> but I don't see any kernel interface that would allow strace to reliably
> recognize this 0x80 case.
I am strongly opposed to fudging registers to half-arsedly slightly
improve the epicly crappy ptrace(2) interface for syscalls.
To fix this right, please just add PTRACE_GET_SYSCALL_INFO or similar
to, in one shot, read out all the syscall details. This means: arch,
no, arg0..arg5, and *whether it's entry or exit*. I propose returning
this structure:
struct ptrace_syscall_info {
u8 op; /* 0 for entry, 1 for exit */
u8 pad0;
u16 pad1;
u32 pad2;
union {
struct seccomp_data syscall_entry;
s64 syscall_exit_retval;
};
};
because struct seccomp_data already gets this right. There's plenty
of opportunity to fine-tune this. Now it works on all architectures.
Since struct seccomp_data may be extended in the future, the operation
should be:
ptrace(PTRACE_GET_SYSCALL_INFO, pid, (void *)sizeof(struct
ptrace_syscall_info), &info);
returns 0 on success and some error code if, for example, the current
ptrace stop isn't a syscall entry or exit.
--Andy
On Wed, Mar 08, 2017 at 08:39:55PM -0800, Andrew Lutomirski wrote:
> On Wed, Mar 8, 2017 at 3:41 PM, Dmitry V. Levin wrote:
[...]
> > Is there any progress with this (or any alternative) solution?
> >
> > I see the kernel side has changed a bit, and the strace part
> > is in a better shape than 5 years ago (although I'm biased of course),
> > but I don't see any kernel interface that would allow strace to reliably
> > recognize this 0x80 case.
>
> I am strongly opposed to fudging registers to half-arsedly slightly
> improve the epicly crappy ptrace(2) interface for syscalls.
>
> To fix this right, please just add PTRACE_GET_SYSCALL_INFO or similar
> to, in one shot, read out all the syscall details. This means: arch,
> no, arg0..arg5, and *whether it's entry or exit*. I propose returning
> this structure:
>
> struct ptrace_syscall_info {
> u8 op; /* 0 for entry, 1 for exit */
> u8 pad0;
> u16 pad1;
> u32 pad2;
> union {
> struct seccomp_data syscall_entry;
> s64 syscall_exit_retval;
> };
> };
>
> because struct seccomp_data already gets this right. There's plenty
> of opportunity to fine-tune this. Now it works on all architectures.
Unfortunately, the API is missing.
Unlike syscall_get_nr(), syscall_get_arch() works with the current task
only so there is no API to get the arch identifier for the given task
that would work on all architectures.
--
ldv