Am 21.12.2015 um 10:23 schrieb Mickaël Salaün:
>>>> Doesn't this break the support for changing syscall numbers using PTRACE_SETREGS?
>>>
>>> The logic is unchanged except updating the UPT_SYSCALL_NR before syscall_trace_enter(). I did my last tests with the x86_32 subarchitecture and all tests (from selftest/seccomp), including PTRACE_SETREGS for syscall numbers tests, passed. However, 2 of this tests still fail for x86_64 (only).
>>
>> No, the logic is different.
>> syscall_trace_enter(regs) enters the ptrace() path and here registers can be changed.
>> Hence "syscall = UPT_SYSCALL_NR(r);" will see the old syscall number.
>> UPT_SYSCALL_NR() returns the syscall number before the ptrace() path...
> 
> The thing is, PTRACE_SETREGS give access to *orig_ax* in the user_regs_struct from arch/x86/include/asm/user_*.h and selftest/seccomp only update this (virtual) register, not the EAX/RAX. Am I missing something?

Sorry, meant orig...

Please see the attached program. It proves that your patch is breaking stuff.
The test is extracted from UML's selftests.

Thanks,
//richard