significance of address 0x8048080

why when i debug asm source in gdb is 0x8048080 the address chosen for the starting entry开发者_JAVA技巧 point into code? this is just a relative offset, not an actual offset of into memory of an instruction, correct?

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There is no special significance to address 0x8048080, but there is one for address 0x08048000.

The latter address is the default address, on which ld starts the first PT_LOAD segment on Linux/x86. On Linux/x86_64, the default is 0x400000, and you can change the default by using a "custom" linker script. You can also change where .text section starts with -Wl,-Ttext,0xNNNNNNNN flag.

After ld starts at 0x08048000, it adds space for program headers, and proceeds to link the rest of the executable according to its built-in linker script, which you can see if you pass in -Wl,--verbose to your link line.

For your program, the size of program headers appears to always be 0x80, so your .text section always starts at 0x8048080, but that is by no means universal.

When I link a trivial int main() { return 0; } program, I get &_start == &.text at 0x8048300, 0x8048178 or 0x8048360, depending on which compiler I use.

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0×8048080 is the default entry point in virtual memory used by the Linux ld linker. You can change it to whatever you want.

for more details check out: http://eli.thegreenplace.net/2011/01/27/how-debuggers-work-part-2-breakpoints/