If gcc is configured with --enable-linker-build-id (as became the case for Arch Linux's avr-gcc package recently when it was bumped to 4.8.0), then it passes --build-id to the linker, and a '.note.gnu.build-id' section is allocated in avr executables at address zero (where the interrupt vector table should be). (See http://gcc.gnu.org/ml/gcc-patches/2010-10/msg00332.html for more on this, in the context of making --enable-linker-build-id the default behavior, which apparently didn't happen.) Strictly speaking, this is a configuration problem, so I will report it to my distribution's package maintainers. However, I suggest that the linker scripts should explicitly shove this section into a black hole, or at least handle it similarly to the '.comment' or debug information sections (i.e., don't allocate any memory for it). Peeking into the avr linker scripts, there doesn't seem to be any any particular handling for it right now. ld's default behavior is apparently just to drop sections it doesn't know about at address zero; and then to dutifully shift the .text section (including the vector table, of course) and all of the jump addresses over by 36 bytes so you can't just strip out the problem section. Steps to reproduce: 1. configure avr-gcc with --enable-linker-build-id 2. compile and link pretty much any avr program 3. run 'avr-objdump -h' or 'readelf -S' (You could also use -Wl,--build-id when linking, but that would just be idiotic.) broken.elf: file format elf32-avr Sections: Idx Name Size VMA LMA File off Algn 0 .note.gnu.build-id 00000024 00000000 00000000 00000094 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 1 .data 00000000 00800100 000000ca 0000015e 2**0 CONTENTS, ALLOC, LOAD, DATA 2 .text 000000a6 00000024 00000024 000000b8 2**1 CONTENTS, ALLOC, LOAD, READONLY, CODE 3 .stab 00000738 00000000 00000000 00000160 2**2 CONTENTS, READONLY, DEBUGGING 4 .stabstr 000000a1 00000000 00000000 00000898 2**0 CONTENTS, READONLY, DEBUGGING 5 .comment 00000011 00000000 00000000 00000939 2**0 CONTENTS, READONLY Disassembly of section .note.gnu.build-id: 00000000 <.note.gnu.build-id>: 0: 04 00 .word 0x0004 ; ???? 2: 00 00 nop 4: 14 00 .word 0x0014 ; ???? 6: 00 00 nop 8: 03 00 .word 0x0003 ; ???? a: 00 00 nop c: 47 4e sbci r20, 0xE7 ; 231 e: 55 00 .word 0x0055 ; ???? 10: c5 c7 rjmp .+3978 ; 0xf9c <__stack+0x69d> 12: 03 77 andi r16, 0x73 ; 115 14: fc 8d ldd r31, Y+28 ; 0x1c 16: c6 07 cpc r28, r22 18: 7f d8 rcall .-3842 ; 0xfffff118 <__eeprom_end+0xff7ef118> 1a: 61 e8 ldi r22, 0x81 ; 129 1c: 68 32 cpi r22, 0x28 ; 40 1e: 49 38 cpi r20, 0x89 ; 137 20: c5 69 ori r28, 0x95 ; 149 22: c4 85 ldd r28, Z+12 ; 0x0c Disassembly of section .text: 00000024 <__vectors>: 24: 0c 94 50 00 jmp 0xa0 ; 0xa0 <__ctors_end> 28: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 2c: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 30: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 34: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 38: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 3c: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 40: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 44: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 48: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 4c: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 50: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 54: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 58: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 5c: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 60: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 64: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 68: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 6c: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 70: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 74: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 78: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 7c: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 80: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 84: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 88: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 8c: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 90: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 94: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 98: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt> 9c: 0c 94 5a 00 jmp 0xb4 ; 0xb4 <__bad_interrupt>
CVSROOT: /cvs/src Module name: src Changes by: nickc@sourceware.org 2013-04-24 15:28:12 Modified files: ld : ChangeLog ld/scripttempl : avr.sc Log message: PR ld/15389 * scripttempl/avr.sc: Add .note.gnu.build-id section. Patches: http://sourceware.org/cgi-bin/cvsweb.cgi/src/ld/ChangeLog.diff?cvsroot=src&r1=1.2579&r2=1.2580 http://sourceware.org/cgi-bin/cvsweb.cgi/src/ld/scripttempl/avr.sc.diff?cvsroot=src&r1=1.17&r2=1.18
Hi Justin, Thanks for the bug report. I have updated the built-in linker script for the AVR linker to add an explicit .note.gnu.build-id section which then ensures that this section does not interfere with the placement of the .text section. Cheers Nick