1382942 - -fno-plt breaks assumption about PIC register

Status: UNCONFIRMED

(NSS :: Libraries, defect, P3)

Description

[Jan Alexander Steffens [:heftig]]

Attachment: no-plt.diff

mpi_x86.s contains macros (GET and PUT) that assume the ebx register contains the GOT pointer. When -fno-plt is in use, this is no longer true (see https://gcc.gnu.org/ml/gcc-patches/2015-05/msg00225.html, second paragraph). Instead, the calling functions place it in other registers like eax and ebp.

The NSS build doesn't finish as shlibsign segfaults.

The attached patch is my naive attempt at working around this by loading the GOT pointer into an unused register. It seems to work, although limits reuse of the macros. I also don't know a way to determine when -fno-plt is in use.

NSS 3.31
Arch Linux i686

Comment 1

[Franziskus Kiefer [:franziskus]]

I see the issue but I wonder why/when you're building with -fno-plt (I don't see you adding -fno-plt in the PKGBUILD and it's not there by default).

Comment 2

[Jan Alexander Steffens [:heftig]]

It was recently added to Arch's default CFLAGS: https://git.archlinux.org/svntogit/packages.git/commit/?h=packages/pacman&id=0cd22d4454e0e1b3ae589b95274f808001465c15

There has been some discussion on our mailing list (e.g. https://lists.archlinux.org/pipermail/arch-dev-public/2017-July/028928.html) and on IRC (no logs).