Date: Sun, 31 Mar 2013 18:53:00 +0300 From: Mikolaj Golub <trociny@FreeBSD.org> To: Konstantin Belousov <kostikbel@gmail.com> Cc: Attilio Rao <attilio@freebsd.org>, freebsd-hackers@freebsd.org, Stanislav Sedov <stas@freebsd.org>, "Robert N. M. Watson" <rwatson@freebsd.org>, Mikolaj Golub <to.my.trociny@gmail.com> Subject: Re: libprocstat(3): retrieve process command line args and environment Message-ID: <20130331155259.GA9867@gmail.com> In-Reply-To: <20130331134047.GN3794@kib.kiev.ua> References: <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> <20130328211820.GA6657@gmail.com> <20130329092245.GU3794@kib.kiev.ua> <20130329123155.GA94024@gmail.com> <20130331134047.GN3794@kib.kiev.ua>
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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
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