[avr-gcc-list] Growing .data section when compiling with GCC 4.0 instead of GCC 3.4.3

[Bernard Fouché]

Hi there.

Since GCC 4.0 has been released, I wanted to give it a try. First I was 
very happy with the optimizer improvements, however I'm stuck with 
something that I don't understand: using the same C code, the same 
avr-libc, I see the .data section growing 218 bytes without any reason.

Here is the .data section compiled with avr-gcc-3.4.3:

Contents of section .data:

800100 6d61696e 2e6300e8 03000017 002d0044  main.c.......-.D
800110 005a0071 0087009e 00b400cb 00e100f8  .Z.q............
800120 000e0125 013b0152 0101bc0b bcff0707  ...%.;.R........
800130 03010000 02040007 7a000100 0001250a  ........z.....%.
800140 0d002e2e 00256c75 002e2e2f 67736d38  .....%lu.../gsm8
800150 2e630070 696e2063 6f646520 3a20000a  .c.pin code : ..
800160 0d002e2e 2f67736d 392e6300 0a0d0047  ..../gsm9.c....G
800170 5053206f 66660a0d 00475053 206f6e0a  PS off...GPS on.
800180 0d00743d 256c750a 0d000d41 542b4346  ..t=%lu....AT+CF
800190 554e3d35 0d000d41 542b4350 494e3d30  UN=5...AT+CPIN=0
8001a0 3030300d 0000                        000... 

Here is the .data section compiled with avr-gcc-4.0:      

Contents of section .data:
800100 6d61696e 2e6300e8 03000017 002d0044  main.c.......-.D
800110 005a0071 0087009e 00b400cb 00e100f8  .Z.q............
800120 000e0125 013b0152 0101bc0b bcff0707  ...%.;.R........
800130 03010000 02040007 7a000100 0001250a  ........z.....%.
800140 0d002e2e 00b8408f 356935b3 3a7d3506  address@hidden:}5.
800150 368c408c 408c4073 358a358c 400f358c  address@hidden@address@hidden@.5.
800160 408c408c 408c408c 408c408c 408c408c  
@address@hidden@address@hidden@address@hidden@address@hidden
800170 408c408c 408c408c 408c40b0 3a6e358c  
@address@hidden@address@hidden@address@hidden:n5.
800180 40b2358c 40ef3823 398c408c 402d398c  @address@hidden@address@hidden
800190 403f39a5 39d039dd 3ae43a0d 3b0e3b9e  @?9.9.9.:.:.;.;.
8001a0 3b043c51 3c513c8f 3ce83ce8 3c293dbe  ;.<Q<Q<.<.<.<)=.
8001b0 3d3e3f9f 3fb83f72 408c408c 408c408c  =>address@hidden@address@hidden@.
8001c0 408c408c 40bb36e6 36f0367a 378d37ef  @address@hidden@.6.6.6z7.7.
8001d0 37093856 3896388c 408c408c 408c408c  address@hidden@address@hidden@.
8001e0 408c40cd 388c408c 40613925 6c75002e  @address@hidden@address@hidden
8001f0 2e2f6773 6d382e63 0070696e 20636f64  ./gsm8.c.pin cod
800200 65203a20 000a0d00 4e4a814a a34aba4a  e : ....NJ.J.J.J
800210 ed4a844b 964bdc4b f54b084c 1b4c4b4c  .J.K.K.K.K.L.LKL
800220 634c904c a74cc94c fe4c0d4d cf4c1e4d  cL.L.L.L.L.M.L.M
800230 244d2a4d 304d384d 4c4d6a4d 2e2e2f67  $M*M0M8MLMjM../g
800240 736d392e 63000a0d 00475053 206f6666  sm9.c....GPS off
800250 0a0d0047 5053206f 6e0a0d00 743d256c  ...GPS on...t=%l
800260 750a0d00 0d41542b 4346554e 3d350d00  u....AT+CFUN=5..
800270 0d41542b 4350494e 3d303030 300d0000  .AT+CPIN=0000...

As one can see, from offset 800145, there are 'unknown' bytes included 
in the .data section. That also happens at offset 80016F.

Do I miss something obvious, or is this a bug in gcc-4.0 ?

Any hint welcome!

 Bernard