Re: [U-Boot] Unaligned memory accesses exception
On Wed, Aug 22, 2018 at 09:44:16AM +0200, Fernando AE wrote: > Hello all, > > I'm bringing up U-Boot for an iMX6UL board, and I've encountered > unaligned memory accesses exceptions while I was trying to test the > ETH commands (e.g., 'ping'). > > After investigation, I found out that the iMX6UL processor traps > unaligned memory accesses by default. As a workaround, I disabled > theses checks, hoping for negligible performance loss. > > I'm wondering if it is a bad idea to disable unaligned memory accesses > during the U-Boot execution, regarding performance issues or other > drawbacks at the kernel level. What exactly do you mean by encountered? Can you post logs? Thanks. -- Tom signature.asc Description: PGP signature ___ U-Boot mailing list U-Boot@lists.denx.de https://lists.denx.de/listinfo/u-boot
Re: [U-Boot] Unaligned memory accesses exception
Hi Fernando, On Wed, Aug 22, 2018 at 5:16 PM, Fernando AE wrote: > Hi Bin, > > The problem lies in these 2 lines, in the ping_send function: > > eth_hdr_size = net_set_ether(net_tx_packet, net_null_ethaddr, PROT_IP); > pkt = (uchar *)net_tx_packet + eth_hdr_size; > > While net_tx_packet is aligned to 32 bits, eth_hdr_size is 14. As a > result 'pkt' is not aligned to 32 bits. Thanks for the information. I see the alignment issue here. > > Further in the code structs like ip_hdr and icmp_hdr (correctly > defined with words aligned to 32 bits) will point to 'pkt', generating > the exceptions. > > Just to highlight, that I'm rather OK with U-Boot having the alignment > exception disabled. I'm just wondering if the kernel expects such > traps enabled or not, and the performance impact of userspace programs > (further developed without alignment in mind). Like I mentioned in the previous email, did you check how other ARMv7 targets behave? Do they turn off this check? My understanding is that newer ARM targets support unaligned access by default. Added Tom to this loop as he has more ARM experience than me. Regards, Bin ___ U-Boot mailing list U-Boot@lists.denx.de https://lists.denx.de/listinfo/u-boot
Re: [U-Boot] Unaligned memory accesses exception
Hi Fernando, On Wed, Aug 22, 2018 at 3:44 PM, Fernando AE wrote: > Hello all, > > I'm bringing up U-Boot for an iMX6UL board, and I've encountered > unaligned memory accesses exceptions while I was trying to test the > ETH commands (e.g., 'ping'). > Have you located the place where this unaligned memory access happens in U-Boot source codes? > After investigation, I found out that the iMX6UL processor traps > unaligned memory accesses by default. As a workaround, I disabled > theses checks, hoping for negligible performance loss. > How does other ARMv7 targets behave? Do they all turn ff the unaligned memory access trap? > I'm wondering if it is a bad idea to disable unaligned memory accesses > during the U-Boot execution, regarding performance issues or other > drawbacks at the kernel level. Regards, Bin ___ U-Boot mailing list U-Boot@lists.denx.de https://lists.denx.de/listinfo/u-boot
[U-Boot] Unaligned memory accesses exception
Hello all, I'm bringing up U-Boot for an iMX6UL board, and I've encountered unaligned memory accesses exceptions while I was trying to test the ETH commands (e.g., 'ping'). After investigation, I found out that the iMX6UL processor traps unaligned memory accesses by default. As a workaround, I disabled theses checks, hoping for negligible performance loss. I'm wondering if it is a bad idea to disable unaligned memory accesses during the U-Boot execution, regarding performance issues or other drawbacks at the kernel level. Thanks for your suggestions. Best regards, Fernando A. E. ___ U-Boot mailing list U-Boot@lists.denx.de https://lists.denx.de/listinfo/u-boot
