Program Execution Flow¶

Reference: Execution Angleboye@Bamboofox.

Static Execution¶

Here is the basic process of static program execution.

Dynamic Execution¶

Here is another more detailed diagram.

Basic Operation Description¶

sys_execve¶

This function is mainly used to execute a new program, i.e., to execute the program we want to run. It checks the corresponding argv, envp, and other parameters.

do_execve¶

This function opens the target image file and reads a specified length (currently 128) of bytes from the beginning of the target file to obtain the basic information of the target file.

search_binary_handler¶

This function searches the binary file type queue that supports handling the current type, in order to allow the handlers of various executable programs to perform the appropriate processing.

load_elf_binary¶

The main processing flow of this function is as follows:

• Check and obtain the header information of the ELF file.

• If the target file uses dynamic linking, use the .interp section to determine the loader path.

• Map the corresponding segments recorded in the program header into memory. The program header contains the following important information:

• The address to which each segment needs to be mapped.

• The corresponding permissions of each segment.
• Records which sections belong to which segments.

The specific mapping is as follows:

Handle different cases:

• In the case of dynamic linking, change the return address of sys_execve to the entry point of the loader (ld.so).
• In the case of static linking, change the return address of sys_execve to the entry point of the program.

ld.so¶

This file has the following functions:

• Mainly used to load the shared libraries recorded in DT_NEED of the ELF file.
• Initialization work:
• Initialize the GOT table.
• Merge the symbol table into the global symbol table.

_start¶

The _start function passes the following items to libc_start_main:

• Starting address of environment variables
• .init
• Initialization work before starting the main function.
• fini
• Cleanup work before program termination.