> the 1st instruction stores R3 at [fp, #-8] and the second instruction can not restores the value from the same address
In bare metal code this usually means you're trying to store to an address which does not actually have any RAM in it. Here R13=00011088, and for the vexpress-a9 board that has a NOR flash device at it, not RAM. RAM starts at 0x60000000. If you link your program to use the RAM at the RAM address you should find it works better. (In earlier versions of QEMU we did have RAM at the 0 address. In real hardware the 0 address is a remappable range which may point to flash or to RAM depending on board configuration. For QEMU we don't model the reconfigurability, and we picked flash because this allows us to run various BIOS-style ROM images. It does unfortunately mean we broke a few odd bare metal images which were relying on the RAM being mapped in there.) -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1549654 Title: qemu-system-arm emulator Status in QEMU: New Bug description: Hi, I don't know if this is a bug or a feature in new QEMU software. I was following an online tutorial using QEMU to develop a simple bare- metal program for qemu-system-arm. I decided to try a more recent software and I got surprised when I found the small code can not run on newer QEMU software (all newer than 2.0.0) but can run on the old QEMU from Ubuntu (Debian 2.0.0+dfsg-2ubuntu1.22) and the stock version from website. After putting the qemu-system-arm in single step and saving the log, the following is the output which you can see the 1st instruction stores R3 at [fp, #-8] and the second instruction can not restores the value from the same address to R0: 0x00010074: e50b3008 str r3, [fp, #-8] R00=00000000 R01=00000000 R02=00000000 R03=0001008c R04=00000000 R05=00000000 R06=00000000 R07=00000000 R08=00000000 R09=00000000 R10=00000000 R11=00011094 R12=00000000 R13=00011088 R14=00010008 R15=00010074 PSR=400001d3 -Z-- A S svc32 ---------------- IN: kmain 0x00010078: e51b0008 ldr r0, [fp, #-8] R00=00000000 R01=00000000 R02=00000000 R03=0001008c R04=00000000 R05=00000000 R06=00000000 R07=00000000 R08=00000000 R09=00000000 R10=00000000 R11=00011094 R12=00000000 R13=00011088 R14=00010008 R15=00010078 PSR=400001d3 -Z-- A S svc32 ---------------- IN: kmain 0x0001007c: ebffffe3 bl 0x10010 R00=00000000 R01=00000000 R02=00000000 R03=0001008c R04=00000000 R05=00000000 R06=00000000 R07=00000000 R08=00000000 R09=00000000 R10=00000000 R11=00011094 R12=00000000 R13=00011088 R14=00010008 R15=0001007c PSR=400001d3 -Z-- A S svc32 -------------------------------------- Meanwhile the older version of QEMU 2.0.0 does this very well and can execute the program normally: 0x00010074: e50b3008 str r3, [fp, #-8] R00=00000000 R01=00000000 R02=00000000 R03=0001008c R04=00000000 R05=00000000 R06=00000000 R07=00000000 R08=00000000 R09=00000000 R10=00000000 R11=00011094 R12=00000000 R13=00011088 R14=00010008 R15=00010074 PSR=400001d3 -Z-- A svc32 ---------------- IN: kmain 0x00010078: e51b0008 ldr r0, [fp, #-8] R00=00000000 R01=00000000 R02=00000000 R03=0001008c R04=00000000 R05=00000000 R06=00000000 R07=00000000 R08=00000000 R09=00000000 R10=00000000 R11=00011094 R12=00000000 R13=00011088 R14=00010008 R15=00010078 PSR=400001d3 -Z-- A svc32 ---------------- IN: kmain 0x0001007c: ebffffe3 bl 0x10010 R00=0001008c R01=00000000 R02=00000000 R03=0001008c R04=00000000 R05=00000000 R06=00000000 R07=00000000 R08=00000000 R09=00000000 R10=00000000 R11=00011094 R12=00000000 R13=00011088 R14=00010008 R15=0001007c PSR=400001d3 -Z-- A svc32 ---------------- The command line to use was: qemu-system-arm -M vexpress-a9 -cpu cortex-a9 -smp 1 -m 64M -nographic -kernel kernel.elf -singlestep -D file.log -d in_asm,cpu The kernel.elf is a simple program (elf) file, created from two sources: boot.S: .global _RESET _RESET: LDR sp, =_STACK BL kmain B . And kernel.c: # define UART0_MEM 0x10009000 volatile unsigned int * const UART0 = (unsigned int *) UART0_MEM; void dprint(const char* message){ while(*message != 0) { *UART0=*message; ++message; } } void kmain() { const char *hi="Hello!"; dprint(hi); }; The linker scripts is: ENTRY(_RESET) SECTIONS { . = 0x10000; .boot . : { boot.o(.text) } .text : { *(.text) } .data : { *(.data) } .bss : { *(.bss COMMON) } . = ALIGN(8); . = . + 0x1000; /* 4kB of stack memory */ _STACK = .; } This error cases the dprint function to find *message as 0 and do not print the output in newer QEMU software. Thank you for consideration. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1549654/+subscriptions
