Greg, As far as my task 2) to properly detect stack overflow, I think the source of my problem is that the __stack_start symbol is not correctly defined.
I found the flthdr -k option to enable the FLAT_FLAG_KTRACE flag for printing the executable layout. > # toolchains/freescale-coldfire-2011.09/bin/m68k-uclinux-flthdr > check-stack-overflow > check-stack-overflow > Magic: bFLT > Rev: 4 > Build Date: Wed Sep 26 16:52:43 2012 > Entry: 0x44 > Data Start: 0x3ca0 > Data End: 0x4544 > BSS End: 0x65f0 > Stack Size: 0x1000 > Reloc Start: 0x4544 > Reloc Count: 0x29 > Flags: 0x12 ( Has-PIC-GOT Kernel-Traced-Load ) When I run the program, I can see that the stack overflow checking is not preventing the stack from getting clobbered. The stack overruns into the BSS, causing the hardware watchdog timer to trip. > / # check-stack-overflow > BINFMT_FLAT: Loading file: /usr/bin/check-stack-overflow > Mapping is 4063c000, Entry point is 44, data_start is 3ca0 > Load /usr/bin/check-stack-overflow: TEXT=4063c040-4063fca0 > DATA=40608004-406088a8 BSS=406088a8-4060a954 > __stack_start = 0x406088b4 > %sp = 0x4060beec > i = 1 > %sp = 0x4060bae0 > i = 2 > %sp = 0x4060b6d4 > i = 3 > %sp = 0x4060b2c8 > i = 4 > %sp = 0x4060aebc > i = 5 > %sp = 0x4060aab0 > i = 6 > %sp > > Watchdog Timer Reset __stack_start (0x406088b4) is clearly wrong; it should have a value greater than the end of the BSS section (0x4060a954). I can see __stack_start has the wrong value in the symbol table. Here's a sorted (by section, address) list of the symbols: > # toolchains/freescale-coldfire-2011.09/bin/m68k-uclinux-objdump -t > check-stack-overflow.gdb > > check-stack-overflow.gdb: file format elf32-m68k > > SYMBOL TABLE: > > > 00000000 w *UND* 00000000 __deregister_frame_info > 00000000 w *UND* 00000000 __h_errno_location > 00000000 w *UND* 00000000 __pthread_initialize_minimal > 00000000 w *UND* 00000000 __register_frame_info > 00000000 w *UND* 00000000 _Jv_RegisterClasses > 00000000 l *ABS* 00000000 EBITS > 00000000 l *ABS* 00000000 EQUAL > 00000000 l *ABS* 00000000 have_current_got > 00000000 l *ABS* 00000000 have_current_got > 00000000 l *ABS* 00000000 NIL > 00000000 l *ABS* 00000000 NOOP [snip] > ffffffff l *ABS* 00000000 LESS > ffffffff l *ABS* 00000000 QUIET_NaN > ffffffff l *ABS* 00000000 UNKNOWN > ffffffff l *ABS* 00000000 UNKNOWN > 00000000 l df *ABS* 00000000 __C_ctype_b.c > 00000000 l df *ABS* 00000000 __errno_location.c > 00000000 l df *ABS* 00000000 __uClibc_main.c [snip] > 00000000 l df *ABS* 00000000 write.c > 00004510 g *ABS* 00000000 _edata > 00000000 l d .text 00000000 .text > 00000004 g .text 00000000 _stext > 00000004 g F .text 00000000 _start [snip] > 00003be0 l F .text 00000000 __do_global_ctors_aux > 00003c0e l F .text 00000000 call___do_global_ctors_aux > 00003c1c l O .text 00000000 __JCR_END__ > 00003c1c l O .text 00000000 __JCR_LIST__ > 00003c20 g F .text 00000000 _init > 00003c34 g F .text 00000000 _fini > 00003c60 g .text 00000000 _etext > 00003c60 g .data 00000000 __data_start > 00003c60 g .data 00000000 _sdata > 00003c60 g .data 00000000 _ssro_size > 00003c60 g .data 00000000 _ssrw_size > 00003c60 g .data 00000000 data_start > 00003c60 l O .data 00000000 _GLOBAL_OFFSET_TABLE_ > 00003c60 l d .data 00000000 .data [snip] > 00004500 l .data 00000000 __fini_array_end > 00004500 l .data 00000000 __fini_array_start > 00004500 l .data 00000000 __init_array_end > 00004500 l .data 00000000 __init_array_start > 00004500 l .data 00000000 __preinit_array_end > 00004500 l .data 00000000 __preinit_array_start > 00004500 l O .eh_frame 00000000 __EH_FRAME_BEGIN__ > 00004500 l O .eh_frame 00000000 __FRAME_END__ > 00004500 l d .eh_frame 00000000 .eh_frame > 00004504 g .bss 00000000 __bss_start > 00004504 g .bss 00000000 _sbss > 00004504 l O .bss 00000001 completed.4562 > 00004504 l d .bss 00000000 .bss > 00004506 l O .bss 00000004 dtor_idx.4564 > 0000450a l O .bss 00000018 object.4577 > 00004524 g O .bss 00000004 _stdio_openlist_del_count > 00004528 g O .bss 00000004 _stdio_openlist_use_count > 0000452c l O .bss 00002000 _fixed_buffers > 0000652c l O .bss 0000000a _bss_custom_printf_spec > 00006538 l O .bss 00000004 __rtld_fini > 0000653c l O .bss 00000004 __app_fini > 00006540 g O .bss 00000004 __pagesize > 00006544 w O .bss 00000004 environ > 00006544 g O .bss 00000004 __environ > 00006548 g O .bss 00000004 __libc_stack_end > 0000654c l O .bss 00000004 been_there_done_that.3075 > 00006550 l O .bss 00000004 __exit_cleanup > 00006554 w O .bss 00000004 _h_errno > 00006554 g O .bss 00000004 h_errno > 00006558 w O .bss 00000004 _errno > 00006558 g O .bss 00000004 errno > 0000655c l O .bss 00000028 _custom_printf_arginfo > 00006584 g O .bss 00000028 .hidden _custom_printf_handler > 000065b0 g .bss 00000000 _ebss > 000065b0 g .bss 00000000 _end > 000065b0 g .bss 00000000 end > 00004510 g .comment 00000000 __stack_start > 00000000 l d .comment 00000000 .comment > 00000000 l d .debug_abbrev 00000000 .debug_abbrev > 00000000 l d .debug_aranges 00000000 .debug_aranges > 00000000 l d .debug_frame 00000000 .debug_frame > 00000000 l d .debug_info 00000000 .debug_info > 00000000 l d .debug_line 00000000 .debug_line > 00000000 l d .debug_loc 00000000 .debug_loc > 00000000 l d .debug_ranges 00000000 .debug_ranges > 00000000 l d .debug_str 00000000 .debug_str I don't know the ld scripting language. I will try to figure out how to define __start_stack to have the same value as, for example, .bss _end. In the mean time, I'll try using _end instead of __stack_start for the stack limit symbol. Larry Baker US Geological Survey 650-329-5608 ba...@usgs.gov
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