Date: Thu, 28 Mar 2013 23:18:21 +0200 From: Mikolaj Golub <trociny@FreeBSD.org> To: Konstantin Belousov <kostikbel@gmail.com> Cc: Stanislav Sedov <stas@freebsd.org>, Attilio Rao <attilio@freebsd.org>, "Robert N. M. Watson" <rwatson@freebsd.org>, freebsd-hackers@freebsd.org Subject: Re: libprocstat(3): retrieve process command line args and environment Message-ID: <20130328211820.GA6657@gmail.com> In-Reply-To: <20130328105134.GO3794@kib.kiev.ua> References: <20130212215054.GA9839@gmail.com> <201302200904.15324.jhb@freebsd.org> <20130220195801.GA8679@gmail.com> <20130316180915.GA91146@gmail.com> <20130316191605.GJ3794@kib.kiev.ua> <20130316223339.GA3534@gmail.com> <20130317063033.GL3794@kib.kiev.ua> <20130317091930.GA2833@gmail.com> <20130324155426.GA87022@gmail.com> <20130328105134.GO3794@kib.kiev.ua>
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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)
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.
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 :-)
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;
Shouldn't we set it to alignment size too? Note also, they set
"Segment is readable" flag.
> >
> > 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?
> Version of what ? MFC does not require any additional actions, FBSD_1.3
> is the valid version namespace in 9 and 8.
Ok. Now I see it was rather silly question :-). Thanks. For this and
your other notes.
--
Mikolaj Golub
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