http://sourceware.org/bugzilla/show_bug.cgi?id=13697
Bug #: 13697
Summary: [avr ] Wrong symbol values with --gc-sections
Product: binutils
Version: 2.23 (HEAD)
Status: NEW
Severity: normal
Priority: P2
Component: ld
AssignedTo: unassig...@sourceware.org
ReportedBy: g...@gcc.gnu.org
Classification: Unclassified
Suppose the following small C program:
int main (void)
{
extern char __heap_start;
return (int) & __heap_start;
}
Compile with:
avr-gcc heap-start.c -mmcu=atmega168 -o heal-start.elf -Os -save-temps
-Wl,-Map,heap-start.map -Wl,--gc-sections
Assembler output is:
.file "heap-start.c"
__SP_H__ = 0x3e
__SP_L__ = 0x3d
__SREG__ = 0x3f
__tmp_reg__ = 0
__zero_reg__ = 1
.section .text.startup,"ax",@progbits
.global main
.type main, @function
main:
.L__stack_usage = 0
ldi r24,lo8(__heap_start)
ldi r25,hi8(__heap_start)
ret
.size main, .-main
.ident "GCC: (GNU) 4.7.0 20120206 (experimental)"
ATmega168 has RAM start at 0x100 but the generated map file reads
...
*(.data)
*(.data*)
*(.rodata)
*(.rodata*)
*(.gnu.linkonce.d*)
0x00800100 . = ALIGN (0x2)
0x00800100 _edata = .
0x00800100 PROVIDE (__data_end, .)
.bss 0x00800060 0x0
0x00800060 PROVIDE (__bss_start, .)
*(.bss)
*(.bss*)
*(COMMON)
0x00800060 PROVIDE (__bss_end, .)
0x0000008a __data_load_start = LOADADDR (.data)
0x0000008a __data_load_end = (__data_load_start
+ SIZEOF (.data))
.noinit 0x00800060 0x0
0x00800060 PROVIDE (__noinit_start, .)
*(.noinit*)
0x00800060 PROVIDE (__noinit_end, .)
0x00800060 _end = .
0x00800060 PROVIDE (__heap_start, .)
...
That is obviously wrong because .bss starts at RAM 0x60.
Notice that the program does not define data in the static storage.
If data in static storage is added or --gc-sectons is removed, the values are
as expected.
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