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Split elf.inc, main asm files manage segments #45

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Jun 18, 2024
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Split elf.inc, main asm files manage segments #45

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4 changes: 2 additions & 2 deletions blue.asm
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Original file line number Diff line number Diff line change
@@ -1,13 +1,13 @@
format elf64 executable 3

include "elf.inc"

segment readable writeable

include "defs.inc"
include "elf_template.inc"

segment readable executable

include "elf.inc"
include "linux.inc"
include "code_buffer.inc"

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109 changes: 0 additions & 109 deletions elf.inc
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@@ -1,113 +1,4 @@

segment readable writeable

;
; adapted from https://kevinboone.me/elfdemo.html
;

elf_binary:
.base_address = 0x400000

elf_binary_headers:
elf_header:
db 0x7f, 0x45, 0x4c, 0x46 ; magic number
db 0x02 ; 64 bit
db 0x01 ; little endian
db 0x01 ; elf version
db 0x00 ; target abi
dq 0x00 ; target abi version + 7 bytes undefined
dw 0x02 ; executable binary
dw 0x3e ; amd64 architecture
dd 0x01 ; elf version
.start_address:
dq -0x01 ; start address
dq 0x40 ; offset to program header
.section_header_offset:
dq -0x01 ; offset to section header
dd 0x00 ; architecture flags
dw 0x40 ; size of header
dw 0x38 ; size of program header
dw 0x01 ; number of program headers
dw 0x40 ; size of section header
dw 0x03 ; number of section headers
dw 0x02 ; index of strtab section header

.length = $ - elf_header
assert .length = 0x40

program_header:
dd 0x01 ; entry type: loadable segment
dd 0x05 ; segment flags: RX
dq 0x00 ; offset within file
dq elf_binary.base_address ; load position in virtual memory
dq elf_binary.base_address ; load position in physical memory
.sizes:
.size_in_file:
dq -0x01 ; size of the loaded section (file)
.size_in_memory:
dq -0x01 ; size of the loaded section (memory)
dq 0x200000 ; alignment boundary for sections

.length = $ - program_header
assert .length = 0x38

shstrtab:
db ".shstrtab"
db 0x00
db ".text"
db 0x00

.length = $ - shstrtab
assert .length = 0x10

elf_binary_section_headers:
section_header_0:
dq 0x00, 0x00, 0x00, 0x00 ; 64 bytes of 0s
dq 0x00, 0x00, 0x00, 0x00

.length = $ - section_header_0
assert .length = 0x40

program_code_section_header:
dd 0x0a ; offset to name in shstrtab
dd 0x01 ; type: program data
dq 0x06 ; flags - executable | in memory
.address:
dq -0x01 ; addr in virtual memory of section
.offset:
dq -0x01 ; offset in the file of this section
.size:
dq -0x01 ; size of this section in the file
dq 0x00 ; sh_link - not used
dq 0x01 ; alignment code (default??)
dq 0x00 ; sh_entsize - not used

.length = $ - program_code_section_header
assert .length = 0x40

shstrtab_section_header:
dd 0x00 ; offset to name in shstrtab
dd 0x03 ; type: string table
dq 0x00 ; flags - none
dq 0x00 ; addr in virtual memory of section - not used
.offset:
dq -0x01 ; offset in the file of this section
.size:
dq -0x01 ; size of this section in the file
dq 0x00 ; sh_link - not used
dq 0x01 ; alignment code (default??)
dq 0x00 ; sh_entsize - not used

.length = $ - shstrtab_section_header
assert .length = 0x40

elf_binary_wrapper_length = $ - elf_binary
elf_binary_headers_length = elf_header.length + program_header.length
elf_binary_section_headers_length = $ - elf_binary_section_headers
elf_binary_section_headers_offset = elf_binary_section_headers - elf_binary

segment readable executable

;
; expects
; - program code entry offset in eax
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105 changes: 105 additions & 0 deletions elf_template.inc
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@@ -0,0 +1,105 @@

;
; adapted from https://kevinboone.me/elfdemo.html
;

elf_binary:
.base_address = 0x400000

elf_binary_headers:
elf_header:
db 0x7f, 0x45, 0x4c, 0x46 ; magic number
db 0x02 ; 64 bit
db 0x01 ; little endian
db 0x01 ; elf version
db 0x00 ; target abi
dq 0x00 ; target abi version + 7 bytes undefined
dw 0x02 ; executable binary
dw 0x3e ; amd64 architecture
dd 0x01 ; elf version
.start_address:
dq -0x01 ; start address
dq 0x40 ; offset to program header
.section_header_offset:
dq -0x01 ; offset to section header
dd 0x00 ; architecture flags
dw 0x40 ; size of header
dw 0x38 ; size of program header
dw 0x01 ; number of program headers
dw 0x40 ; size of section header
dw 0x03 ; number of section headers
dw 0x02 ; index of strtab section header

.length = $ - elf_header
assert .length = 0x40

program_header:
dd 0x01 ; entry type: loadable segment
dd 0x05 ; segment flags: RX
dq 0x00 ; offset within file
dq elf_binary.base_address ; load position in virtual memory
dq elf_binary.base_address ; load position in physical memory
.sizes:
.size_in_file:
dq -0x01 ; size of the loaded section (file)
.size_in_memory:
dq -0x01 ; size of the loaded section (memory)
dq 0x200000 ; alignment boundary for sections

.length = $ - program_header
assert .length = 0x38

shstrtab:
db ".shstrtab"
db 0x00
db ".text"
db 0x00

.length = $ - shstrtab
assert .length = 0x10

elf_binary_section_headers:
section_header_0:
dq 0x00, 0x00, 0x00, 0x00 ; 64 bytes of 0s
dq 0x00, 0x00, 0x00, 0x00

.length = $ - section_header_0
assert .length = 0x40

program_code_section_header:
dd 0x0a ; offset to name in shstrtab
dd 0x01 ; type: program data
dq 0x06 ; flags - executable | in memory
.address:
dq -0x01 ; addr in virtual memory of section
.offset:
dq -0x01 ; offset in the file of this section
.size:
dq -0x01 ; size of this section in the file
dq 0x00 ; sh_link - not used
dq 0x01 ; alignment code (default??)
dq 0x00 ; sh_entsize - not used

.length = $ - program_code_section_header
assert .length = 0x40

shstrtab_section_header:
dd 0x00 ; offset to name in shstrtab
dd 0x03 ; type: string table
dq 0x00 ; flags - none
dq 0x00 ; addr in virtual memory of section - not used
.offset:
dq -0x01 ; offset in the file of this section
.size:
dq -0x01 ; size of this section in the file
dq 0x00 ; sh_link - not used
dq 0x01 ; alignment code (default??)
dq 0x00 ; sh_entsize - not used

.length = $ - shstrtab_section_header
assert .length = 0x40

elf_binary_wrapper_length = $ - elf_binary
elf_binary_headers_length = elf_header.length + program_header.length
elf_binary_section_headers_length = $ - elf_binary_section_headers
elf_binary_section_headers_offset = elf_binary_section_headers - elf_binary
5 changes: 4 additions & 1 deletion elf_test.asm
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Original file line number Diff line number Diff line change
@@ -1,9 +1,12 @@
format elf64 executable 3

include "elf.inc"
segment readable writeable

include "elf_template.inc"

segment readable executable

include "elf.inc"
include "linux.inc"

program_code:
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10 changes: 6 additions & 4 deletions elf_test_hello_world.asm
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Original file line number Diff line number Diff line change
@@ -1,16 +1,17 @@
format elf64 executable 3

include "linux.inc"
include "elf.inc"

segment readable writeable

include "elf_template.inc"

fstat_buffer:
rb 48
.file_size:
rq 1
rb 88

segment readable executable

program_code:
.entry_offset = $ - program_code
db 0x48, 0xc7, 0xc0 ; mov rax, 1 - sys_write
Expand All @@ -32,7 +33,8 @@ program_code:

.length = $ - program_code

segment readable executable
include "elf.inc"
include "linux.inc"

expected_output_size = elf_binary_wrapper_length + program_code.length

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