Dear QEMU community, I'm now trying to fix bug in glibc which became apparent on qemu 6.0.0.
The error is caused by glibc commit: bca0f5cbc9257c13322b99e55235c4f21ba0bd82 https://sourceware.org/git/?p=glibc.git;a=blobdiff;f=sysdeps/arm/dl-machine.h;h=eb13cb8b57496a0ec175c54a495f7e78db978fb7;hp=ff5e09e207f7986b1506b8895ae6c2aff032a380;hb=bca0f5cbc9257c13322b99e55235c4f21ba0bd82;hpb=34b4624b04fc8f038b2c329ca7560197320615b4 (reverting it causes the board to boot again) Other components: binutils_2.37 gcc_11.2 Yocto poky: SHA1: 1e2e9a84d6dd81d7f6dd69c0d119d0149d10ade1 Qemu start line (the problem is visible on 5.2.0 and 6.0.0): qemu-system-arm -device virtio-net-device,netdev=net0,mac=52:54:00:12:34:02 -netdev tap,id=net0,ifnam e=tap0,script=no,downscript=no -object rng-random,filename=/dev/urandom,id=rng0 -device virtio-rng-pci,rng=rng0 -drive id=disk0,file=y2038-image-devel-qemuarm.ext4,if=none,format =raw -device virtio-blk-device,drive=disk0 -device qemu-xhci -device usb-tablet -device usb-kbd -machine virt,highmem=off -cpu cortex-a15 -smp 4 -m 256 -serial mon:stdio -serial null -nographic -device VGA,edid=on -kernel zImage--5.10.62+git0+bce2813b16_machine-r0-qemuarm-20210910095636.bin -append 'root=/dev/vda rw mem=256M ip=192.168.7.2::192.168.7.1:255.255.255.0 console=ttyAMA0 console=hvc0 vmalloc=256 It has been tested with Cortex-A9 (Vexpress A9 2 core board) and Cortex-A15. I've also tested the v5.1, v5.10 and v5.14 kernels. The error is persistent. I do add -s and -S when starting qemu-system-arm. I can use gdb to debug the kernel without issues. Unfortunately, I'm not able to debug /sbin/init after switching contex to user space. Moreover, gdbserver cannot be used as the error (and kernel OOPs) is caused when early code from ld-linux.so.3 (the _dl_start function) is executed. Any hints on how to debug it? Inspecting assembler is one (awkward) option (some results presented below). I can also inspect the VMA of the code just before starting the /sbin/init process. Unfortunately, when I try to break on user space code it is not very helpful (as -S -s are supposed to be used with kernel). Some info with the eligible code (_dl_start function): ------------------------------------------------------ I think that the problem may be with having the negative value calculated. The relevant snipet: 116c: bf00 nop 116e: bf00 nop 1170: bf00 nop 1172: f8df 3508 ldr.w r3, [pc, #1288] ; 167c <_dl_start+0x520> 1176: f8df 1508 ldr.w r1, [pc, #1288] ; 1680 <_dl_start+0x524> 117a: 447b add r3, pc 117c: 4479 add r1, pc 117e: f8c3 1598 str.w r1, [r3, #1432] ; 0x598 1182: bf00 nop 1184: bf00 nop 1186: bf00 nop 1188: bf00 nop 118a: bf00 nop 118c: bf00 nop 118e: f8df 24f4 ldr.w r2, [pc, #1268] ; 1684 <_dl_start+0x528> 1192: f8d3 5598 ldr.w r5, [r3, #1432] ; 0x598 1196: 447a add r2, pc 1198: 442a add r2, r5 119a: 1a52 subs r2, r2, r1 119c: f8c3 25a0 str.w r2, [r3, #1440] ; 0x5a0 11a0: 6813 ldr r3, [r2, #0] 167c: 0002be92 .word 0x0002be92 1680: ffffee80 .word 0xffffee80 The r1 gets the 0xffffee80 (negative offset) value. It is then added to pc and used to calculate r2. For working code (aforementioned patch reverted) - there are NO such large values (like aforementioned 0xffffee80). The arithmetic is done on 1690: 00000020 .word 0x00000020 1694: 0002be7e .word 0x0002be7e which seems to work. Maybe I'm missing some flag when I do start qemu-system-arm? Thanks in advance for help and hints. -- Best regards, Łukasz Majewski
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