Messages in this thread | | | Date | Fri, 27 Feb 2015 16:57:40 +0800 | From | Chung-Lin Tang <> | Subject | Re: nios2: is the ptrace ABI correct? |
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On 15/2/25 10:07 PM, Arnd Bergmann wrote: > On Wednesday 25 February 2015 08:33:16 Ezequiel Garcia wrote: >> >> /me is more confused now >> >> In arch/nios2/include/asm/ucontext.h >> >> struct ucontext { >> unsigned long uc_flags; >> struct ucontext *uc_link; >> stack_t uc_stack; >> struct mcontext uc_mcontext; >> sigset_t uc_sigmask; >> }; >> >> And in include/uapi/asm-generic/ucontext.h: >> >> struct ucontext { >> unsigned long uc_flags; >> struct ucontext *uc_link; >> stack_t uc_stack; >> struct sigcontext uc_mcontext; >> sigset_t uc_sigmask; >> }; >> >> Which one is the one that userspace sees? And why does the kernel has >> two different structures? > > Userspace sees the asm-generic header, which I assume is a bug > in this case.
Yes, I believe nios2 doesn't not need this asm-generic/ucontext.h header; OTOH it just isn't used; no real harm done, so easily fixed.
>> Given this oddities, I'm wondering how troublesome would be to just >> re-do this and break the ptrace and signal ABI. For instance, just >> pushing pt_regs in PTRACE_GETREGSET would make things much clearer. > > Could you change pt_regs to match the layout you have for PTRACE_GETREGSET > instead? It seems much more intuitive.
There is a reason for this pt_regs arrangement: the nios2 syscall interface uses r4-r9 for parameters, while the usual C conventions use only r4-r7, placing r8-r9 at the start of pt_regs creates a natural stack layout for entering C code after the asm shims in entry.S
>> I guess Linus would burn me for even suggesting to breaking users... but >> do we have any users at all? This arch has just been mainlined. Altera's >> out-of-tree is already ABI-incompatible with mainline so that's not an >> issue. >> >> The only one using this ABI is gdb, which is easily fixed. > > You can change anything you like as long as nobody complains about > regressions.
PTRACE_GET/SETREGSET is a new feature in nios2-linux that we're still about to support in upstream GDB, so things could be fixed if needed, but why can't you just use the [0...] ordering in userspace?
BTW, it's even that way in signal stacks as well; nios2 does not use/export sigcontext inside struct ucontext. We just use a int[32] array there.
Thanks, Chung-Lin
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