Date: Tue, 14 Feb 2017 16:56:44 +0000 From: Andrew Turner <andrew@fubar.geek.nz> To: Mark Millard <markmi@dsl-only.net> Cc: Shawn Webb <shawn.webb@hardenedbsd.org>, Tom Vijlbrief <tvijlbrief@gmail.com>, freebsd-arm <freebsd-arm@freebsd.org> Subject: Re: A potential fix for arm64's: sh`forkshell child-process path after fork sometimes has a bad stack pointer value Message-ID: <20170214165644.15dedf6e@zapp> In-Reply-To: <3BC697B9-4A3E-49FF-AB11-1106E2EF8399@dsl-only.net> References: <DC3CC3BE-9D8C-41ED-ADD0-AFD4019B2E90@dsl-only.net> <2D04FF37-DEC8-42CE-961D-AE8CD58A0EAA@dsl-only.net> <93064627-5F72-4167-90B1-0A98ABF4C99C@dsl-only.net> <3BC697B9-4A3E-49FF-AB11-1106E2EF8399@dsl-only.net>
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On Tue, 14 Feb 2017 08:35:54 -0800 Mark Millard <markmi@dsl-only.net> wrote: > The following change has let my test run for 8.5 hours so far without > a fork-failure in sh`forkshell : > > # svnlite diff /usr/src/sys/arm64/arm64/swtch.S > Index: /usr/src/sys/arm64/arm64/swtch.S > =================================================================== > --- /usr/src/sys/arm64/arm64/swtch.S (revision 312982) > +++ /usr/src/sys/arm64/arm64/swtch.S (working copy) > @@ -241,6 +241,12 @@ > mov fp, #0 /* Stack traceback stops here. */ > bl _C_LABEL(fork_exit) > > + /* > + * Disable interrupts to avoid > + * overwriting sp_el0 and spsr_el1 by an IRQ exception. > + */ > + msr daifset, #2 > + > /* Restore sp and lr */ > ldp x0, x1, [sp] > msr sp_el0, x0 > @@ -263,12 +269,6 @@ > ldp x28, x29, [sp, #TF_X + 28 * 8] > /* Skip x30 as it was restored above as lr */ > > - /* > - * Disable interrupts to avoid > - * overwriting spsr_el1 by an IRQ exception. > - */ > - msr daifset, #2 > - > /* Restore elr and spsr */ > ldp x0, x1, [sp, #16] > msr elr_el1, x0 > > I'm going to switch to attempting a self-hosted buildworld > buildkernel again. Can you try the patch in https://reviews.freebsd.org/D9593. It moves loading of sp_el0 until after interrupts have been disabled. Andrew
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