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Executable and Linkable Format
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Executable and Linkable Format
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================================================================================
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================================================================================
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ELF (Executable and Linkable Format) is a standard file format for executable files and shared libraries. Linux as many UNIX-like operating systems uses this format. Let's look on structure of the ELF-64 Object File Format and some defintions in the linux kernel source code related with it.
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ELF (Executable and Linkable Format) is a standard file format for executable files and shared libraries. Linux, as well as, many UNIX-like operating systems uses this format. Let's look on structure of the ELF-64 Object File Format and some defintions in the linux kernel source code related with it.
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An ELF object file consists of the following parts:
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An ELF object file consists of the following parts:
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@ -16,7 +16,7 @@ Now let's look closer on these components.
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It's located in the beginning of the object file. It's main point is to locate all other parts of the object file. File header contains following fields:
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It's located in the beginning of the object file. It's main point is to locate all other parts of the object file. File header contains following fields:
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* ELF identification - array of bytes which helps to identify the file as an ELF object file and also provides information about general object file characteristic;
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* ELF identification - array of bytes which helps to identify the file as an ELF object file and also provides information about general object file characteristic;
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* Object file type - identifies the object file type. This field can describe that ELF file is relocatable object file, executable file, etc...;
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* Object file type - identifies the object file type. This field can describe that ELF file is a relocatable object file, executable file, etc...;
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* Target architecture;
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* Target architecture;
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* Version of the object file format;
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* Version of the object file format;
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* Virtual address of the program entry point;
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* Virtual address of the program entry point;
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@ -51,7 +51,7 @@ This structure defined in the [elf.h](https://github.com/torvalds/linux/blob/mas
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**Sections**
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**Sections**
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All data stores in a sections in an Elf object file. Sections identified by index in the section header table. Section header contains following fields:
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All data is stored in sections in an Elf object file. Sections identified by index in the section header table. Section header contains following fields:
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* Section name;
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* Section name;
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* Section type;
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* Section type;
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@ -102,12 +102,12 @@ in the linux kernel source code.
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`elf64_phdr` defined in the same [elf.h](https://github.com/torvalds/linux/blob/master/include/uapi/linux/elf.h).
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`elf64_phdr` defined in the same [elf.h](https://github.com/torvalds/linux/blob/master/include/uapi/linux/elf.h).
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And ELF object file also contains other fields/structures which you can find in the [Documentation](http://www.uclibc.org/docs/elf-64-gen.pdf). Better let's look on the `vmlinux`.
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And ELF object file also contains other fields/structures which you can find in the [Documentation](http://www.uclibc.org/docs/elf-64-gen.pdf). Now let's look on the `vmlinux`.
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vmlinux
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vmlinux
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--------------------------------------------------------------------------------
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--------------------------------------------------------------------------------
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`vmlinux` is relocatable ELF object file too. So we can look on it with the `readelf` util. First of all let's look on a header:
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`vmlinux` is relocatable ELF object file too. So we can look at it with the `readelf` util. First of all let's look on a header:
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```
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```
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$ readelf -h vmlinux
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$ readelf -h vmlinux
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