libprocstat(3): retrieve process command line args and environment

[Konstantin Belousov]

On Thu, Mar 28, 2013 at 11:18:21PM +0200, Mikolaj Golub wrote:
> On Thu, Mar 28, 2013 at 12:51:34PM +0200, Konstantin Belousov wrote:
> 
> > In the generic Elf 64bit draft specification I have, the notes sections
> > are specified to consists of entries, each of which is an array of 8-byte
> > words. I think we are right using the 8-byte alignment.
> 
> I have impression many implementations use 4-byte alignment. E.g. in
> NetBSD:
> 
> sys/kern/core_elf32.c:
> 
> #define ELFROUNDSIZE    4       /* XXX Should it be sizeof(Elf_Word)? */
> #define elfround(x)     roundup((x), ELFROUNDSIZE)
Note that this is core_elf32. I am concerned with the 64-bit cores.

> 
> Also, we have inconsistency with imgactl_elf.c/parse_notes(), which
> uses 4-byte alignment:
> 
> 		note = (const Elf_Note *)((const char *)(note + 1) +
> 		    roundup2(note->n_namesz, sizeof(Elf32_Addr)) +
> 		    roundup2(note->n_descsz, sizeof(Elf32_Addr)));
> 
> I suppose there were no issues before, because accidentally the sizes
> of all notes we had were 8 bytes aligned.
Indeed, both ABI and NOINIT notes have size which is multiple of 8.

> 
> Now, when I add new notes it will break things. I don't have strong
> opinion, it will be ok for me to leave 8-byte alignment and fix
> issues, just want to have strong support here :-)
Well, while the issue is discussed and decided, you could just make
your new notes size be multiple of 8 too.

> 
> BTW, looking at NetBSD code I see they set p_align in the note
> segement to ELFROUNDSIZE:
> 
>         /* Write out the PT_NOTE header. */
>         ws.psections->p_type = PT_NOTE;
>         ws.psections->p_offset = notestart;
>         ws.psections->p_vaddr = 0;
>         ws.psections->p_paddr = 0;
>         ws.psections->p_filesz = notesize;
>         ws.psections->p_memsz = 0;
>         ws.psections->p_flags = PF_R;
>         ws.psections->p_align = ELFROUNDSIZE;
> 
> while we set to 0:
> 
> 	/* The note segement. */
> 	phdr->p_type = PT_NOTE;
> 	phdr->p_offset = hdrsize;
> 	phdr->p_vaddr = 0;
> 	phdr->p_paddr = 0;
> 	phdr->p_filesz = notesz;
> 	phdr->p_memsz = 0;
> 	phdr->p_flags = 0;
> 	phdr->p_align = 0;
You mean, for the core dumps ?

> 
> Shouldn't we set it to alignment size too? Note also, they set
> "Segment is readable" flag.
I think both changes are fine.

I skimmed over the usermode parts of the patch. One thing I did not liked
is the mis-handling of the read() return values. If there is short read,
the errno value is meaningless, but warn() would still append it to
the message. I suggest to explicitely distinguish -1 and >= 0 returns
from reads.
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