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

[Mikolaj Golub]

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.

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?

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