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Re: bfd_arch_info.fill vs ARM (bug 13616)
- From: Roland McGrath <mcgrathr at google dot com>
- To: Roland McGrath <mcgrathr at google dot com>, "binutils at sourceware dot org" <binutils at sourceware dot org>, Richard Earnshaw <rearnsha at arm dot com>
- Date: Wed, 1 Feb 2012 09:27:15 -0800
- Subject: Re: bfd_arch_info.fill vs ARM (bug 13616)
- References: <x57jmx93y487.fsf@frobland.mtv.corp.google.com> <20120201165357.GC392@e103070-lin.arm.com>
Perhaps you missed my original posting about this, when I was first trying
to address it in the assembler (which is not sufficient, as HJ pointed out).
Some particular targets mandate that all portions of executable segments
(even unreachable code) be valid instructions. Targets with such a
requirement may vary on which, if any, trapping instructions are valid
enough for their constraints. The simplest, safest, and most efficient
(for processor instruction prefetch and so forth) choice is to use nop
instructions. (This is not an issue of ELF or even of psABIs, it's an
issue of particular systems. Systems that don't care just don't care--a
nop is as good as a zero--so it's not worth the complexity to make detail
this more specific than per-machine.)
Thanks,
Roland