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

[Konstantin Belousov]

On Sun, Mar 31, 2013 at 06:53:00PM +0300, Mikolaj Golub wrote:
> On Sun, Mar 31, 2013 at 04:40:47PM +0300, Konstantin Belousov wrote:
> 
> > I inspected imgact_elf.c:parse_note(), imgact_elf.c:putnote() and
> > rtld.c:digest_notes(). Only  putnote() uses 8-byte alignment.
> > Every other OS and our !coredump code assumes 4-byte alignment.
> 
> Thanks!
>  
> > Does changing the putnote() to align on the 4-byte boundary cause
> > real change in the core file notes layout ?
> 
> Currently, we store only 4 types of notes in a core file:
> 
> #define	NT_PRSTATUS	1	/* Process status. */
> #define	NT_FPREGSET	2	/* Floating point registers. */
> #define	NT_PRPSINFO	3	/* Process state info. */
> #define	NT_THRMISC	7	/* Thread miscellaneous info. */
> 
> I checked the sizes of structures inserted into the notes, and on amd64
> they all are multiple of 8:
> 
> (kgdb) p sizeof(prpsinfo_t) % 8
> $1 = 0
> (kgdb) p sizeof(prstatus_t) % 8
> $2 = 0
> (kgdb) p sizeof(prfpregset_t) % 8
> $3 = 0
> (kgdb) p sizeof(thrmisc_t) % 8
> $4 = 0
> 
> so both 4-byte and 8-byte aligned.
Well, FreeBSD supports some more 64bit architectures, besides amd64.
At least on powerpc64, I get
prpsinfo 120 0
prstatus_t 344 0
prfpregset_t 264 0
thrmisc_t 24 0

Second column is sizeof(), third is sizeof() % 8. This is in fact not
much surprising, since all ABIs define the alignment of the structure
as the alignment of the most demanding member. And, because 64bit
architectures have 8-byte registers, it is indeed expected that the
size % 8 == 0.

> 
> I believe that the patch below will not change the current core file
> notes layout, will make things consistent in our tree, and will make
> adding my procstat notes easier, if I use 4-byte alignment.
> 
> Are you ok if I commit it before introducing my changes?
Yes, I believe this is the right thing to do.

> 
> Index: sys/kern/imgact_elf.c
> ===================================================================
> --- sys/kern/imgact_elf.c	(revision 248706)
> +++ sys/kern/imgact_elf.c	(working copy)
> @@ -1538,10 +1538,10 @@ __elfN(putnote)(void *dst, size_t *off, const char
>  	*off += sizeof note;
>  	if (dst != NULL)
>  		bcopy(name, (char *)dst + *off, note.n_namesz);
> -	*off += roundup2(note.n_namesz, sizeof(Elf_Size));
> +	*off += roundup2(note.n_namesz, sizeof(Elf32_Size));
>  	if (dst != NULL)
>  		bcopy(desc, (char *)dst + *off, note.n_descsz);
> -	*off += roundup2(note.n_descsz, sizeof(Elf_Size));
> +	*off += roundup2(note.n_descsz, sizeof(Elf32_Size));
>  }
>  
>  static boolean_t
> 
> Also, shouldn't we update then the following comment in sys/elf_common.h?
> 
> /*
>  * Note header.  The ".note" section contains an array of notes.  Each
>  * begins with this header, aligned to a word boundary.  Immediately
>  * following the note header is n_namesz bytes of name, padded to the
>  * next word boundary.  Then comes n_descsz bytes of descriptor, again
>  * padded to a word boundary.  The values of n_namesz and n_descsz do
>  * not include the padding.
>  */
> 
> -- 
> Mikolaj Golub
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