hello_world_len
points to the special st_shndx == SHN_ABS == 0xF1FF
.0xF1FF
is chosen so as to not conflict with other sections.st_value == 0xD == 13
which is the value we have stored there on the assembly: the length of the string Hello World!
.This is small optimization that our assembler does for us and which has ELF support.
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