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Notes for the Qemu MIPS port
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I) Example usage:
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# ln -s u-boot.bin mips_bios.bin
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start it:
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qemu-system-mips -L . /dev/null -nographic
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or
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if you use a qemu version after commit 4224
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create image:
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# dd of=flash bs=1k count=4k if=/dev/zero
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# dd of=flash bs=1k conv=notrunc if=u-boot.bin
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start it:
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# qemu-system-mips -M mips -pflash flash -monitor null -nographic
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II) How to debug U-Boot
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In order to debug U-Boot you need to start qemu with gdb server support (-s)
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and waiting the connection to start the CPU (-S)
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# qemu-system-mips -S -s -M mips -pflash flash -monitor null -nographic
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in an other console you start gdb
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1) Debugging of U-Boot Before Relocation
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Before relocation, the addresses in the ELF file can be used without any problems
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buy connecting to the gdb server localhost:1234
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# mipsel-unknown-linux-gnu-gdb u-boot
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GNU gdb 6.6
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Copyright (C) 2006 Free Software Foundation, Inc.
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GDB is free software, covered by the GNU General Public License, and you are
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welcome to change it and/or distribute copies of it under certain conditions.
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Type "show copying" to see the conditions.
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There is absolutely no warranty for GDB. Type "show warranty" for details.
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This GDB was configured as "--host=i486-linux-gnu --target=mipsel-unknown-linux-gnu"...
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(gdb) target remote localhost:1234
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Remote debugging using localhost:1234
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_start () at start.S:64
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64 RVECENT(reset,0) /* U-boot entry point */
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Current language: auto; currently asm
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(gdb) b board.c:289
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Breakpoint 1 at 0xbfc00cc8: file board.c, line 289.
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(gdb) c
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Continuing.
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Breakpoint 1, board_init_f (bootflag=<value optimized out>) at board.c:290
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290 relocate_code (addr_sp, id, addr);
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Current language: auto; currently c
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(gdb) p/x addr
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$1 = 0x87fa0000
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2) Debugging of U-Boot After Relocation
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For debugging U-Boot after relocation we need to know the address to which
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U-Boot relocates itself to 0x87fa0000 by default.
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And replace the symbol table to this offset.
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(gdb) symbol-file
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Discard symbol table from `/private/u-boot-arm/u-boot'? (y or n) y
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Error in re-setting breakpoint 1:
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No symbol table is loaded. Use the "file" command.
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No symbol file now.
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(gdb) add-symbol-file u-boot 0x87fa0000
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add symbol table from file "u-boot" at
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.text_addr = 0x87fa0000
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(y or n) y
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Reading symbols from /private/u-boot-arm/u-boot...done.
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Breakpoint 1 at 0x87fa0cc8: file board.c, line 289.
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(gdb) c
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Continuing.
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Program received signal SIGINT, Interrupt.
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0xffffffff87fa0de4 in udelay (usec=<value optimized out>) at time.c:78
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78 while ((tmo - read_c0_count()) < 0x7fffffff)
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