Bug#943798: ld.so: old Arm ABI detection patch causing problems, time to remove?

[Steve McIntyre <steve@einval.com>]

Source: glibc
Version: 2.28-10
Severity: important

Hi folks,

It looks like my old Arm ABI detection patch for ld.so is causing
problems for people using LLVM. I've been contacted by a developer,
referring to a mailing list thread:

  https://lists.llvm.org/pipermail/llvm-dev/2019-October/135993.html

It looks like the LLVM version of strip is more aggressive than the
GNU binutils version, and this is causing problems - it's stripping
the .ARM.attributes data and that's causing problems with our extra
checks for the Tag_ABI_VFP_args setting. Whether that's a valid thing
to do or not is an argument for another day, I think... However,
checking with the bzip2 binaries that the reporter provided I can see
that they have the right ABI flag in the ELF header but we're still
running the extra ABI check:

(sid-armhf)steve@mjolnir:~/abi$ LD_PRELOAD=./libbz2.so.all ./bzip2 
ERROR: ld.so: object './libbz2.so.all' from LD_PRELOAD cannot be preloaded (cannot open shared object file): ignored.
bzip2: I won't write compressed data to a terminal.
bzip2: For help, type: `bzip2 --help'.

(sid-armhf)steve@mjolnir:~/abi$ readelf -a libbz2.so.all | grep "^  Flags"
  Flags:                             0x5000400, Version5 EABI, hard-float ABI

I think this is wrong, and I can't think of why I didn't find this
earlier when I was working in this area. :-/

So: I think we have two sensible options:

1. I find time now to fix up ld.so to only do the extra check here if
   we think it's needed

OR

2. Just remove the patch for extra check here - it was always the plan
   that this would go away after a while once people were unlikely to
   still be running binaries from the pre ELF-header toolchains.

Checking history, I can see that the binutils changes for those ELF
header changes landed in Debian back in Nov 2012. (Wow, time
flies!). Given that, I'd now be strongly in favour of just dropping the
patch in

debian/patches/arm/unsubmitted-ldso-abi-check.diff

as it's now safely obsolete. What do others think?

-- System Information:
Debian Release: 10.1
  APT prefers stable-debug
  APT policy: (500, 'stable-debug'), (500, 'stable'), (500, 'oldstable')
Architecture: amd64 (x86_64)

Kernel: Linux 4.19.0-6-amd64 (SMP w/4 CPU cores)
Kernel taint flags: TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8), LANGUAGE=en_GB:en (charmap=UTF-8)
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled