20 KiB
| title | TARGET DECK | FILE TAGS | tags | |||
|---|---|---|---|---|---|---|
| ELF | Obsidian::STEM | linker::elf x86-64 |
|
Overview
Modern x86-64/index Linux systems use the ELF (Executable and Linkable Format) object file format.
%%ANKI Basic What object file format do modern x86-64 Linux machines typically use? Back: ELF. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI Basic What is the ELF object file format an acronym for? Back: Executable and Linkable Format. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI Basic What is ELF an example of? Back: An object file format. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
Relocatable Object Files
!
%%ANKI Basic A relocatable object file is typically broken up into what three regions? Back: The header, sections, and the section header table. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI Basic In a relocatable object file, what exists between the header and section header table? Back: The sections. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI Cloze A relocatable object file consists of a {header}, {sections}, and a {section header table}, in that order. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI Basic Where in a relocatable object file does the section header table exist? Back: At the end. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
Sections
A typical ELF object file contains the following sections:
.text
The machine code of the compiled program.
%%ANKI
Basic
What does the .text section of an ELF file contain?
Back: The machine code of the compiled program.
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI
Basic
Which ELF section typically contains the machine code of the compiled program?
Back: .text
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI
Cloze
The {.text} section contains the {machine code} of the compiled program.
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
.rodata
Read-only data such as the format strings in c17/strings/printf statements and conditions#JMP for switch statements.
%%ANKI
Basic
What does the .rodata section of an ELF file contain?
Back: Read-only data.
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI
Basic
Which ELF section typically contains read-only data?
Back: .rodata
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI
Basic
Why is the .rodata section named the way it is?
Back: It stands for read-only data.
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI
Basic
In what section of an ELF file would a printf format string be found in?
Back: .rodata
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: c17::printf
END%%
%%ANKI
Basic
In what section of an ELF file would a jump table be found in?
Back: .rodata
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
.data
Global and static C variables initialized to a non-zero value.
%%ANKI
Basic
What kind of global/static C variables does the .data section of an ELF file contain?
Back: Those initialized to a non-zero value.
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: c17
END%%
%%ANKI
Basic
Which ELF section contains global C variables initialized to a non-zero value?
Back: .data
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: c17
END%%
%%ANKI
Basic
Which ELF section contains static C variables initialized to a non-zero value?
Back: .data
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: c17
END%%
%%ANKI Basic Which ELF section contains local C variables initialized to a non-zero value? Back: N/A. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016. Tags: c17
END%%
%%ANKI
Basic
Consider the following translation unit. Which ELF section will foo end up in?
int foo = 1;
Back: .data
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: c17
END%%
%%ANKI
Basic
Consider the following translation unit. Which ELF section will bar end up in?
int foo() {
int bar = 0;
}
Back: N/A. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016. Tags: c17
END%%
%%ANKI
Basic
Consider the following translation unit. Which ELF section will bar end up in?
int foo() {
static int bar = 1;
}
Back: .data.
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: c17
END%%
.tdata
Thread-local global and static C variables initialized to a non-zero value.
%%ANKI
Basic
What kind of global/static C variables does the .tdata section of an ELF file contain?
Back: Thread-local variables initialized to a non-zero value.
Reference: Ulrich Drepper, “ELF Handling For Thread-Local Storage,” n.d.
Tags: c17
END%%
%%ANKI
Basic
Which ELF section contains global thread-local C variables initialized to a non-zero value?
Back: .tdata
Reference: Ulrich Drepper, “ELF Handling For Thread-Local Storage,” n.d.
Tags: c17
END%%
%%ANKI
Basic
Which ELF section contains static thread-local C variables initialized to a non-zero value?
Back: .tdata
Reference: Ulrich Drepper, “ELF Handling For Thread-Local Storage,” n.d.
Tags: c17
END%%
%%ANKI
Basic
Consider the following translation unit. Which ELF section will foo end up in?
_Thread_local int foo = 1;
Back: .tdata
Reference: Ulrich Drepper, “ELF Handling For Thread-Local Storage,” n.d.
Tags: c17
END%%
%%ANKI
Basic
Consider the following translation unit. Which ELF section will bar end up in?
int foo() {
static _Thread_local int bar = 1;
}
Back: .tdata.
Reference: Ulrich Drepper, “ELF Handling For Thread-Local Storage,” n.d.
Tags: c17
END%%
%%ANKI
Basic
Consider the following translation unit. Which ELF section will bar end up in?
int foo() {
_Thread_local int bar = 1;
}
Back: N/A. Compilation error - bar must have global storage.
Reference: Ulrich Drepper, “ELF Handling For Thread-Local Storage,” n.d.
Tags: c17
END%%
.bss
Uninitialized global and static C variables, along with any global or static variables initialized to zero.
%%ANKI
Basic
What kind of global/static C variables does the .bss section of an ELF file contain?
Back: Unitialized variables or those initialized to zero.
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: c17
END%%
%%ANKI
Basic
Which ELF section contains uninitialized global C variables?
Back: .bss
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: c17
END%%
%%ANKI
Basic
Which ELF section contains global C variables initialized to a zero value?
Back: .bss
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: c17
END%%
%%ANKI
Basic
Which two ELF sections contain global/static C variables?
Back: .data and .bss
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: c17
END%%
%%ANKI
Basic
Consider the following translation unit. Which ELF section will foo end up in?
int foo = 0;
Back: .bss
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: c17
END%%
%%ANKI
Basic
Consider the following translation unit. Which ELF section will foo end up in?
int foo;
Back: .bss
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: c17
END%%
%%ANKI
Basic
Both .bss and .data hold what kind of C variables?
Back: Global or static variables.
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: c17
END%%
%%ANKI
Basic
Which of .data and/or .bss is considered a placeholder?
Back: .bss
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI
Basic
What does Bryant et al. mean by saying .bss is "merely a placeholder"?
Back: The .bss section occupies no actual space in the object file.
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI
Basic
How does the size of the .bss section compare to that of the .data section?
Back: Less than or equal since the .bss section is always empty.
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI
Basic
What mneumonic does Bryant et al. suggest to remember the .bss and .data distinction?
Back: .bss is a backronym for "Better Save Space!"
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI
Basic
Consider the following translation unit. Which ELF section will bar end up in?
int foo() {
static int bar = 0;
}
Back: .bss.
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: c17
END%%
.tbss
Uninitialized global and static thread-local C variables, along with any global or static thread-local variables initialized to zero.
%%ANKI
Basic
What kind of global/static C variables does the .tbss section of an ELF file contain?
Back: Unitialized thread-local variables or those initialized to zero.
Reference: Ulrich Drepper, “ELF Handling For Thread-Local Storage,” n.d.
Tags: c17
END%%
%%ANKI
Basic
Which ELF section contains uninitialized thread-local global C variables?
Back: .tbss
Reference: Ulrich Drepper, “ELF Handling For Thread-Local Storage,” n.d.
Tags: c17
END%%
%%ANKI
Basic
Which ELF section contains global thread-local C variables initialized to a zero value?
Back: .tbss
Reference: Ulrich Drepper, “ELF Handling For Thread-Local Storage,” n.d.
Tags: c17
END%%
%%ANKI
Basic
Which two ELF sections contain global/static thread-local C variables?
Back: .tdata and .bss
Reference: Ulrich Drepper, “ELF Handling For Thread-Local Storage,” n.d.
Tags: c17
END%%
%%ANKI
Basic
Consider the following translation unit. Which ELF section will foo end up in?
_Thread_local int foo = 0;
Back: .tbss
Reference: Ulrich Drepper, “ELF Handling For Thread-Local Storage,” n.d.
Tags: c17
END%%
%%ANKI
Basic
Consider the following translation unit. Which ELF section will foo end up in?
_Thread_local int foo;
Back: .tbss
Reference: Ulrich Drepper, “ELF Handling For Thread-Local Storage,” n.d.
Tags: c17
END%%
%%ANKI
Basic
Both .tbss and .tdata hold what kind of C variables?
Back: Global or static thread-local variables.
Reference: Ulrich Drepper, “ELF Handling For Thread-Local Storage,” n.d.
Tags: c17
END%%
%%ANKI
Basic
Which of .tdata and/or .tbss is considered a "placeholder"?
Back: .tbss
Reference: Ulrich Drepper, “ELF Handling For Thread-Local Storage,” n.d.
Tags: c17
END%%
%%ANKI
Basic
How does the size of the .tbss section compare to that of the .tdata section?
Back: Less than or equal since the .tbss section is always empty.
Reference: Ulrich Drepper, “ELF Handling For Thread-Local Storage,” n.d.
Tags: c17
END%%
%%ANKI
Basic
Consider the following translation unit. Which ELF section will bar end up in?
int foo() {
static _Thread_local int bar = 0;
}
Back: .tbss.
Reference: Ulrich Drepper, “ELF Handling For Thread-Local Storage,” n.d.
Tags: c17
END%%
.symtab
A symbol table with information about functions and global variables defined and referenced in the program.
%%ANKI
Basic
What does the .symtab section of an ELF file contain?
Back: A symbol table for functions and global variables.
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI
Basic
Which ELF section contains a symbol table for functions and global variables?
Back: .symtab
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI
Basic
Why is the .symtab ELF section named the way it is?
Back: It's short for symbol table.
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
.rel.text
A list of locations in the .text section that will need to be modified when the linker combines this object file with others.
%%ANKI
Basic
What does the .rel.text section of an ELF file contain?
Back: Relocation entries for the .text section.
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI
Basic
Why is the .rel.text ELF section named the way it is?
Back: It's short for relocation entries for the .text section.
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI
Cloze
The {.rel.text} section contains {relocation entries} for the .text section.
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
.rel.data
A list of locations in the .data section that will need to be modified when the linker combines this object file with others.
%%ANKI
Basic
What does the .rel.data section of an ELF file contain?
Back: Relocation entries for the .data section.
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI
Basic
Why is the .rel.data ELF section named the way it is?
Back: It's short for relocation entries for the .data section.
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI
Cloze
The {.rel.data} section contains {relocation entries} for the .data section.
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
.strtab
A string table for the symbol tables in the .symtab section as well as for section names in the section headers. It is a sequence of NUL-terminated character strings.
%%ANKI
Basic
What does the .strtab section of an ELF file contain?
Back: A string table.
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI
Basic
Why is the .strtab ELF section named the way it is?
Back: It is short for string table.
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI
Basic
The .strtab provides information for what other, non-debug ELF section?
Back: .symtab
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
%%ANKI
Basic
Section names are contained in what ELF section?
Back: .strtab
Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
END%%
Bibliography
- Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
- Ulrich Drepper, “ELF Handling For Thread-Local Storage,” n.d.