Date: Thu, 30 Nov 2017 23:03:46 +0000 From: bugzilla-noreply@freebsd.org To: freebsd-arm@FreeBSD.org Subject: [Bug 224008] UBLDR doesn't save registers correctly in start.S Message-ID: <bug-224008-7@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D224008 Bug ID: 224008 Summary: UBLDR doesn't save registers correctly in start.S Product: Base System Version: 11.1-RELEASE Hardware: arm OS: Any Status: New Severity: Affects Some People Priority: --- Component: arm Assignee: freebsd-arm@FreeBSD.org Reporter: parakleta@darkreality.org Created attachment 188440 --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=3D188440&action= =3Dedit Save and Restore U-Boot registers. Using `ubldr.bin` I was getting intermittent behaviour depending on which options I compiled into U-Boot. Eventually I discovered that the issue is = that the entry point in `sys/boot/arm/uboot/start.S` is not correctly saving and restoring registers. Most importantly the r9 register is the base of the global data and this is not typically a callee-saved register, but must be = for U-Boot. There is a change to this file on April 2 by "ian" which saves the argument= and return address but it doesn't go far enough. My patch is to applied to the state before that patch. Essentially the important caller-saved registers are pushed (r0, r1, r9, lr) before the relocation call, and popped after. Then r8/r9 are saved as usual for the syscall trampoline, and lr is stored in r8 (now free) as a callee-s= aved value before calling into `main`. The call to `main` can no longer be a tail call because we must restore r9 especially after main returns (although since we have used r8 to hold lr we must also restore this). I don't know how this affects the ELF version, but this patch is critical f= or the correct functioning of the binary version of UBLDR. --=20 You are receiving this mail because: You are the assignee for the bug.=
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