lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Message-ID: <20210211143059.GE28121@gate.crashing.org> Date: Thu, 11 Feb 2021 08:30:59 -0600 From: Segher Boessenkool <segher@...nel.crashing.org> To: Christophe Leroy <christophe.leroy@...roup.eu> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>, Paul Mackerras <paulus@...ba.org>, Michael Ellerman <mpe@...erman.id.au>, npiggin@...il.com, linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] powerpc/bug: Remove specific powerpc BUG_ON() On Thu, Feb 11, 2021 at 03:09:43PM +0100, Christophe Leroy wrote: > Le 11/02/2021 à 12:49, Segher Boessenkool a écrit : > >On Thu, Feb 11, 2021 at 07:41:52AM +0000, Christophe Leroy wrote: > >>powerpc BUG_ON() is based on using twnei or tdnei instruction, > >>which obliges gcc to format the condition into a 0 or 1 value > >>in a register. > > > >Huh? Why is that? > > > >Will it work better if this used __builtin_trap? Or does the kernel only > >detect very specific forms of trap instructions? > > We already made a try with __builtin_trap() 1,5 year ago, see > https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20510ce03cc9463f1c9e743c1d93b939de501b53.1566219503.git.christophe.leroy@c-s.fr/ > > The main problems encountered are: > - It is only possible to use it for BUG_ON, not for WARN_ON because GCC > considers it as noreturn. Is there any workaround ? A trap is noreturn by definition: -- Built-in Function: void __builtin_trap (void) This function causes the program to exit abnormally. > - The kernel (With CONFIG_DEBUG_BUGVERBOSE) needs to be able to identify > the source file and line corresponding to the trap. How can that be done > with __builtin_trap() ? The DWARF debug info should be sufficient. Perhaps you can post-process some way? You can create a trap that falls through yourself (by having a trap-on condition with a condition that is always true, but make the compiler not see that). This isn't efficient though. Could you file a feature request (in bugzilla)? It is probably useful for generic code as well, but we could implement this for powerpc only if needed. Segher
Powered by blists - more mailing lists