"ps -e" without procfs(5)

[Kostik Belousov]

On Sat, Nov 05, 2011 at 08:59:21PM +0200, Mikolaj Golub wrote:
> 
> On Sat, 5 Nov 2011 17:44:43 +0200 Kostik Belousov wrote:
> 
>  >>  KB> I think that the aux vector must be naturally aligned. You can return
>  >>  KB> ENOEXEC early if vptr is not aligned.
>  >> 
>  >> Not sure I see what you mean. vptr for auxv is calculated just couple lines
>  >> above, and I check the result here, in the part common for all vector types.
>  KB> You do not check for the alignment. Am I wrong ?
> 
> I see now. If natural alignment means "addr % sizeof(aux) == 0" then the aux
> vectors are not naturally aligned. After adding this check:
> 
>     if (vptr % sizeof(aux) != 0)
>     	return (ENOEXEC);
No, the natural alignment of the structure is the alignment of the most
demanding member. So it is 4 bytes on 32bit, and 8 bytes on 64.

> 
> I started to observe many ENOEXEC errors. Adding printf showed that the
> vectors are half size aligned.
> 
> On i386:
> 
> get_proc_vector(pid = getty[3442], type = 2): vptr (2143284876) % sizeof(aux) (8) = 4)
> 
> On amd64:
> 
> get_proc_vector(pid = getty[2425], type = 2): vptr (140737488346568) % sizeof(aux) (16) = 8)
> 
> Looking at exec_copyout_strings() from kern_exec.c, how destp is calculated, I
> think they are sizeof(char *) aligned.
> 
> Do you think it is worth adding the check for sizeof(char *) alignment?
> 
>     if (vptr % (sizeof(char *) != 0)
>     	return (ENOEXEC);
I suggest to use #if __ELF_WORD_SIZE == 32 or 64.
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