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

[Mikolaj Golub]

Here is an updated patch set, which I think includes all kib's
suggestions. It also introduces procstat groups, umask, rlimit, and
osrel notes.

http://people.freebsd.org/~trociny/procstat_core.3.patch

Sbuf section interface looks like below:

/* start a section */
sbuf_start_section(sb, NULL);
/* write something to sbuf */
...
/* start a subsection (need to save the current section length) */
sbuf_start_section(sb, &old_len);
/* write something to sbuf */
...
/* end a subsection padding to 4 bytes with '\0' bytes 
  (need to provide the previously saved section length) */
sbuf_end_section(sb, old_len, 4, 0);
...
 /* aling the whole section to page size */
sbuf_end_section(sb, -1, PAGE_SIZE, 0);

Open issues/questions:

1) I would also like to make libprocstat(3) extract environment, args,
and auxv from the core. It looks like I don't need to store envv and
argv in notes, as it is already present in the core. But I think I
need to know psstrings to find them.

Would it be ok, if I add auxv and psstrings notes, and extract envv
and agrv from a program section in the core?

2) I started NT_PROCSTAT constants from the first not used number in
elf_common.h, i.e. 8. But in this case they conflict with those
available on other systems:

contrib/binutils/include/elf/common.h:

#define NT_PSTATUS  10      /* Has a struct pstatus */
#define NT_FPREGS   12      /* Has a struct fpregset */
#define NT_PSINFO   13      /* Has a struct psinfo */
#define NT_LWPSTATUS    16      /* Has a struct lwpstatus_t */
#define NT_LWPSINFO 17      /* Has a struct lwpsinfo_t */
#define NT_WIN32PSTATUS 18      /* Has a struct win32_pstatus */

Although note name = "FreeBSD" should have disambiguated this, readelf
looks like ignores this and its output for my core on i386 looks
confusing:

  Owner         Data size       Description
  FreeBSD               0x0000006c      NT_PRPSINFO (prpsinfo structure)
  FreeBSD               0x00000068      NT_PRSTATUS (prstatus structure)
  FreeBSD               0x000000b0      NT_FPREGSET (floating point registers)
  FreeBSD               0x00000018      NT_THRMISC (thrmisc structure)
  FreeBSD               0x00000304      Unknown note type: (0x00000008)
  FreeBSD               0x00000a6c      Unknown note type: (0x00000009)
  FreeBSD               0x000008d4      NT_PSTATUS (pstatus structure)
  FreeBSD               0x0000000c      Unknown note type: (0x0000000b)
  FreeBSD               0x00000006      NT_FPREGS (floating point registers)
  FreeBSD               0x000000d4      NT_PSINFO (psinfo structure)
  FreeBSD               0x00000008      Unknown note type: (0x0000000e)

Should I use some other range for NT_PROCSTAT notes?

3) Following our current code I align notes to sizeof(Elf_Size), which
is 4 on i386 and 8 on amd64.

But I have an issue reading the notes by readelf on amd64, which alway
uses 4 byte alignment:

contrib/binutils/binutils/readelf.c:

      next = (Elf_External_Note *)(inote.descdata + align_power (inote.descsz, 2));

where

  #define align_power(addr, align)    \
  (((addr) + ((bfd_vma) 1 << (align)) - 1) & ((bfd_vma) -1 << (align)))

Should I change alignment to 4 bytes?

4) In libprocstat I added new functions and placed them under already
existent FBSD_1.3 version section in Symbol.map.

Shouldn't I bump the version? Won't I need any additional care if I
want to MFC the code to stable/9 and may be 8?

-- 
Mikolaj Golub