Sixteen or more bytes of uninitialized data will cause ld to generate an
incorrect opcode in __do_clear_bss in the startup for the avr target as
shown in this example.
Source file, a.S:
.comm x,16,1
.global __do_copy_data
.global __do_clear_bss
.global main
main:
cpi r26,lo8(16)
rjmp main
Compile script:
FLAGS="-m avr4 -Tdata 0x800100 -L/usr/local/lib/gcc/avr/4.0.2/avr4"
avr-as a.S -o a.o
avr-ld $FLAGS -o a.hex /usr/local/avr/lib/avr4/crtm88.o --oformat=ihex \
a.o -lgcc -lc
avr-ld $FLAGS -o a.elf /usr/local/avr/lib/avr4/crtm88.o a.o -lgcc -lc
avr-objdump -dSCg a.elf > a.lst
Output a.lst, lines 68,69,77,78:
00000060 <.do_clear_bss_start>:
60: a0 31 cpi r26, 0x10 ; 16
0000006a <main>:
6a: a0 31 cpi r26, 0x10 ; 16
Output a.hex, lines 8,11:
:100056001160A0E1B16001C01D92B031B107E1F7B6
:04006A00A031FECFF4
The listing is correct for both cpi instructions, "a0 31", but the hex
file is wrong for the first, "B031", though it's correct for the second,
"A031". And, indeed, test programs fail to execute on real hardware with
16 or more bytes of BSS, but _do_ execute with less.
The first cpi instruction is in function __do_clear_bss in source file
gcc-4.0.2/gcc/config/avr/libgcc.S. But gcc itself doesn't seem be be
involved, other than supplying the code, which is assembled by avr-as (or
directly by avr-ld?). It's not clear how the hex is generated or where
the error occurs.
I'm using Mandriva Linux 2006 (2.6.12-12mdk) and compiled from source
binutils-2.16.1, gcc-4.0.2, and avr-libc-1.4.3.
$ avr-ld -V
GNU ld version 2.16.1
Supported emulations:
avr2
avr1
avr3
avr4
avr5
Note: I thank everyone that works on binutils.
--
Summary: Incorrect opcode in __do_clear_bss if bss has more than
15 bytes
Product: binutils
Version: 2.16
Status: NEW
Severity: normal
Priority: P2
Component: ld
AssignedTo: unassigned at sources dot redhat dot com
ReportedBy: KenJackson at ieee dot org
CC: bug-binutils at gnu dot org
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: avr
http://sourceware.org/bugzilla/show_bug.cgi?id=2378
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