This is the mail archive of the mailing list for the binutils project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: Don't add DT_DEBUG to MIPS shared libraries

Richard Sandiford wrote:
This patch is the first in a series to support prelinking on MIPS.

The prelinker uses DT_DEBUG as a heuristic to distinguish shared
libraries from position-independent executables.  However, the
"traditional MIPS" bfd target creates DT_DEBUG tags for all dynamic
objects.  This would cause all unused shared libraries to be entered
into the prelink cache as "not prelinkable", which affects -q prelinks
if those libraries are later used by new executables.

The traditional MIPS target was added for mips-dde-sysv4.2MP.
I can't find any discussion in the archives about why that target
needed DT_DEBUG tags to be added to shared libraries (or indeed
whether it was needed for correctness at all, rather than just being
something that was done for consistency with the native tools).

It's very difficult to keep a target like mips-dde-sysv4.2MP
working with so little information.  Given that the tag is of
no use on GNU/Linux targets, and given that the DT_DEBUG heuristic
could well be used by tools other than the prelinker, I think it's
best to just be consistent with other targets.  This patch therefore
removes DT_DEBUG tags from shared libraries and makes sure that the
PIEs do indeed get DT_DEBUG and DT_MIPS_RLD_MAP tags.

Tested on mips{,64}{,el}-{elf,linux-gnu} and mips-sgi-irix6.5.
OK to install?


bfd/ * elfxx-mips.c (_bfd_mips_elf_size_dynamic_sections): Add DT_DEBUG and DT_MIPS_RLD_MAP tags for position-independent executables. Do not add DT_DEBUG to shared libraries for any MIPS target.

	* ld-mips-elf/multi-got-1.d: Remove DT_DEBUG tag.  Do not require
	a specific file offset for .dynamic.  Reduce DT_HASH by 8 to account
	for removed tag.
	* ld-mips-elf/tls-multi-got-1.r: Likewise.  Also reduce DT_REL by 8.
	Reduce PLTGOT and symbol values by 16 to account for the removed tag.
	* ld-mips-elf/textrel-1.d: Remove DT_DEBUG tag.
	* ld-mips-elf/rel32-n32.d: Reduce addresses by 16 to account for
	removed DT_DEBUG tag.
	* ld-mips-elf/rel64.d: Likewise.
	* ld-mips-elf/ Likewise.
	* ld-mips-elf/ Likewise.

This may break libgcj. I think the boehm-gc uses DT_DEBUG in

Looking at the code now, It is difficult to see how it ever worked right. I have some local uClibc patches for it, but it has been a while since I worked with it, so the issue is a little unclear to me right now.

Given that I am probably a bit confused is no reason to not do this. I just wanted to note that there may be the potential for breakage.

Really I think it is a good idea as I would very much like to to pre-linking. On the off chance that it does break libgcj, I will fix it.

David Daney

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]