Date: Thu, 14 Aug 2014 10:13:26 -0600 From: Warner Losh <imp@bsdimp.com> To: John Baldwin <jhb@freebsd.org> Cc: Marcel Moolenaar <marcel@freebsd.org>, Phil Shafer <phil@juniper.net>, John-Mark Gurney <jmg@funkthat.com>, "Simon J. Gerraty" <sjg@juniper.net>, arch@freebsd.org, Poul-Henning Kamp <phk@phk.freebsd.dk>, freebsd-arch <freebsd-arch@freebsd.org>, Konstantin Belousov <kostikbel@gmail.com> Subject: Re: XML Output: libxo - provide single API to output TXT, XML, JSON and HTML Message-ID: <94A47A7D-89C9-4504-B669-2A5EDA80373B@bsdimp.com> In-Reply-To: <201408140847.00573.jhb@freebsd.org> References: <20140814052648.GM2737@kib.kiev.ua> <201408140606.s7E66XXA091972@idle.juniper.net> <20140814085257.GN2737@kib.kiev.ua> <201408140847.00573.jhb@freebsd.org>
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[-- Attachment #1 --] On Aug 14, 2014, at 6:47 AM, John Baldwin <jhb@freebsd.org> wrote: >>> Marking the binary with a libxo-specific note tells the caller that >>> the binary is capable of rendering its output in a non-traditional >>> style and gives the caller a means of triggering those styles of >>> output. In the libxo-enabled world, I see this as vital information >>> the caller needs to initialize the environment in which the command >>> will be run. Isn't this exactly the sort of information ELF targets >>> for note sections? >> >> How binary format has any relevance for an application level feature ? >> What would you do with the binaries which permissions are 'r-s--x--x', >> which is not unexpected for the tools which gather system information >> and have to access things like /dev/mem ? >> >> You removed and did not answered a crusial question, which is a litmus >> test for your proposal. Namely, how presence of the proposed note in >> the binary is different from DT_NEEDED tag for your library ? > > Yes, checking DT_NEEDED for libxo.so is the first thing I thought of as well. > It is equivalent to 'ldd foo | grep libxo'. Doesn’t work for static binaries, nor for cases where libxo is linked in by a library indirectly, nor for when the command is a shell script that may invoke a command that supports this output, nor for a python script that implements this output, etc. My question for people advocating this method: Why not require all commands that generate this kind of output to support a standard command line option that causes the command to print nothing and return 0 if it supports reporting, or anything else if it doesn’t (return 0 with output, or return non-zero with or without output). This would handle the more complicated implementation issues with using DT_NEEDED and/or the ELF note, be more in line with how things are traditionally done, and offer greater flexibility of implementation. Warner [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Comment: GPGTools - https://gpgtools.org iQIcBAEBCgAGBQJT7OAmAAoJEGwc0Sh9sBEAEPQQAJLliSBIX1ZOzojPmD3OMQjX JydNjyQxCL/8e9nwp3DbAJT3jdSuJCLNaPcyUr+9+bq49NNCGhHunyE6ORTewJRB Mn59lTRdrjNs1xFB8ZWjBuJgiWdMIyu14z9TJChm7x2wiTIjxW0bDJVfWlaGfVSU iYF+v039ethCGvHBEIFrX4nuovIqehMrcen1nnSd3MjjMSm3Q4/BZQpANpfmWVwN R2yjZkFG2YbfdxmlpRoAIMePHHcpAO3wD3UYTV0kcjHixFtkvJ3fGcdG6cowV17Q E9b3UkjbqrMmRuR+O+BzIBKepFzNmrSfmawwXxnGTU8wOhpWkSEaO6y0egtkNPCw KFYyaTspL0DjEY2jfsEw0sPqfMiexMV6qLivHQ+vNMFNJZIcE20mCJ3EhTXyW9FC 7PWoneU4L3v/QjsPmIlfwgule7rq+nuucCMPBFM4wzvegL7fZfr7gHw1VrUTScIy lKiQkD4Th+CTzGpmdj2p9EdmN9Us9Q7ZSBrTji8VyfDB+lIjtMcBzsaO6MeXiQjV Uh6M3O6O4yl8/PkTGbohQhyugJeTqN5S1hc9Y0yl+ui0q868WbW77LcSjU0DAV23 ou726heAes/0NuYgCdnwY8skV1lTX8CUVDhsCOy4x+1Fp725RPniafRr2MlqAgYl +04+85NTYfZOtHUZKmou =e42H -----END PGP SIGNATURE-----
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