Hi all, Looking at stack unwinding on AVR, I noticed the current frame was not always correctly detected from the function prologue. This bug occurs only with the following prologue, referred to as "Method 2: Adjust stack pointer" in GCC: gcc/config/avr/avr.c (avr_prologue_setup_frame). --> push the old frame pointer push r28 push r29 --> allocate new space rcall .+0 push r1 --> move fp <- sp in r28, 0x3d in r29, 0x3e GCC uses "rcall .+0" and "push r1" to adjust the stack pointer, "rcall" pushing automatically 2 or 3 bytes on the stack, depending on the target. GDB should scan this prologue and find out the size of the frame but it is incorrect by one because it expects "push r0" and not "push r1". I believe this register was changed in GCC withcommit 915f904be. Best, Pierre 2014-03-18 Pierre Langlois * avr-tdep.c (avr_scan_prologue): Accept push r1 instruction for small stack allocation. ----------------------------------------------------------------------------------------- GNU gdb (AVR 8-bit toolchain (built 20140310)) 7.7.50.20140318-cvs Copyright (C) 2014 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "--host=x86_64-unknown-linux-gnu --target=avr". Type "show configuration" for configuration details. For bug reporting instructions, please see: . Find the GDB manual and other documentation resources online at: . For help, type "help". Type "apropos word" to search for commands related to "word". (gdb) file atmega-test.elf Reading symbols from atmega-test.elf...done. (gdb) target remote :51000 Remote debugging using :51000 0x00000116 in multiply (a=25, b=8) at main.c:4 4 return a * b; (gdb) monitor reset (gdb) load Loading section .text, size 0x1a4 lma 0x0 Start address 0x0, load size 420 Transfer rate: 3360 bits in <1 sec, 210 bytes/write. (gdb) b multiply Breakpoint 1 at 0x114: file main.c, line 4. (gdb) c Continuing. Program received signal SIGTRAP, Trace/breakpoint trap. 0x00000116 in multiply (a=25, b=8) at main.c:4 4 return a * b; (gdb) bt #0 0x00000116 in multiply (a=25, b=8) at main.c:4 #1 0x01e00000 in ?? () (gdb) q A debugging session is active. Inferior 1 [Remote target] will be killed. Quit anyway? (y or n)