From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60140) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YsIFU-00021a-QG for qemu-devel@nongnu.org; Tue, 12 May 2015 18:02:02 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YsIFT-0005CF-Ry for qemu-devel@nongnu.org; Tue, 12 May 2015 18:02:00 -0400 Received: from mailapp01.imgtec.com ([195.59.15.196]:2764) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YsIFT-0005Bz-Lz for qemu-devel@nongnu.org; Tue, 12 May 2015 18:01:59 -0400 From: Leon Alrae Date: Tue, 12 May 2015 23:01:38 +0100 Message-ID: <1431468101-5419-3-git-send-email-leon.alrae@imgtec.com> In-Reply-To: <1431468101-5419-1-git-send-email-leon.alrae@imgtec.com> References: <1431468101-5419-1-git-send-email-leon.alrae@imgtec.com> MIME-Version: 1.0 Content-Type: text/plain Subject: [Qemu-devel] [PATCH v2 2/5] hw/mips: Do not clear BEV for MIPS malta kernel load List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: matthew.fortune@imgtec.com, aurelien@aurel32.net From: Matthew Fortune The BEV flag controls whether the boot exception vector is still in place when starting a kernel. When cleared the exception vector at EBASE (or hard coded address of 0x80000000) is used instead. The early stages of the linux kernel would benefit from BEV still being set to ensure any faults get handled by the boot rom exception handlers. This is a moot point for system qemu as there aren't really any BEV handlers, but there are other good reasons to change this... The UHI (semi-hosting interface) defines special behaviours depending on whether an application starts in an environment with BEV set or cleared. When BEV is set then UHI assumes that a bootloader is relatively dumb and has no advanced exception handling logic. However, when BEV is cleared then UHI assumes that the bootloader has the ability to handle UHI exceptions with its exception handlers and will unwind and forward UHI SYSCALL exceptions to the exception vector that was installed prior to running the application. Signed-off-by: Matthew Fortune Signed-off-by: Leon Alrae --- hw/mips/mips_malta.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/hw/mips/mips_malta.c b/hw/mips/mips_malta.c index d3f2cd3..e1b2e20 100644 --- a/hw/mips/mips_malta.c +++ b/hw/mips/mips_malta.c @@ -885,7 +885,7 @@ static void main_cpu_reset(void *opaque) read only location. The kernel location and the arguments table location does not change. */ if (loaderparams.kernel_filename) { - env->CP0_Status &= ~((1 << CP0St_BEV) | (1 << CP0St_ERL)); + env->CP0_Status &= ~(1 << CP0St_ERL); } malta_mips_config(cpu);