Most of these are various methods to execute code before or after the “main” program itself and most live in crtstuff.c ( https://github.com/gcc-mirror/gcc/blob/master/libgcc/crtstuff.c ). They exist to support features of various C-like programming languages, but they can be accessed in C as well. It perhaps seems over complicated because some of these represent legacy baggage … Read more
The problem is that replacing call printf@PLT with call [printf@GOTPLT] requires that the compiler knows that the function printf exists in a shared library and not a static library (or even in just a plain object file). The linker can change call printf into call printf@PLT, jmp printf into jmp printf@PLT or even mov eax, … Read more
You can also skip the ar command and use readelf, via something like: readelf -h <archive>.a | grep ‘Class\|File\|Machine’ [00:32:15] /usr/lib $ readelf -h libxslt.a | grep ‘Class\|File\|Machine’ File: libxslt.a(attrvt.o) Class: ELF32 Machine: Intel 80386 File: libxslt.a(xslt.o) Class: ELF32 Machine: Intel 80386 … #Trimmed this, it goes on a bit File: libxslt.a(transform.o) Class: ELF32 Machine: … Read more
Use the -O binary output format: objcopy -O binary –only-section=.text foobar.elf foobar.text Just verified with avr-objcopy and an AVR ELF image’s .text section. Note that if, as Tim points out below, your section doesn’t have the ALLOC flag, you may have to add –set-section-flags .text=alloc to be able to extract it.
If everything else fails, you could read the documentation, starting with man strip. Seriously, maybe your application has a lot of symbols and code. At one extreme, the biggest size reduction would be rm elf but then your program won’t run anymore. It all depends on your program and what you coded into it. As … Read more
Has been some time since i worked with ELF. But i think i still remember this stuff. No, it does not physically contain those zeros. If you look into an ELF file program header, then you will see each header has two numbers: One is the size in the file. And another is the size … Read more
What is a DSO? A DSO is a Dynamic Shared Object, or less formally a shared library. What is a hidden symbol? A hidden symbol is a symbol (i.e. name of function or data object) that has been compiled with hidden linkage, e.g. as per the (GCC specific) declaration: int x __attribute__ ((visibility (“hidden”))); If … Read more
from binutils/readelf.c: /* The difference between readelf and objdump: Both programs are capabale of displaying the contents of ELF format files, so why does the binutils project have two file dumpers ? The reason is that objdump sees an ELF file through a BFD filter of the world; if BFD has a bug where, say, … Read more
The R_X86_64_32S and R_X86_64_64 are names of relocation types, for code compiled for the amd64 architecture. You can look all of them up in the amd64 ABI. According to it, R_X86_64_64 is broken down to: R_X86_64 – all names are prefixed with this 64 – Direct 64 bit relocation and R_X86_64_32S to: R_X86_64 – prefix … Read more
Consider the following: Symbol table .symtab contains 1203 entries: Num: Value Size Type Bind Vis Ndx Name 310: a0008120 0 NOTYPE GLOBAL DEFAULT ABS _gp 734: a0000010 32 OBJECT GLOBAL DEFAULT 77 v 818: 9d000018 496 FUNC GLOBAL DEFAULT 71 main 849: a0000124 4 OBJECT GLOBAL DEFAULT 78 phrase 955: a0000000 9 OBJECT GLOBAL DEFAULT … Read more