ilo-amd64-openbsd: use libc instead of direct syscalls
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crc
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commit
a4832ca8c9
2 changed files with 72 additions and 87 deletions
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@ -1,6 +1,7 @@
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/* AMD64 ilo, (c) 2023 Christopher Leonard, MIT License */
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.global _start
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.global main
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.extern open, read, write, close, exit, lseek
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/* rax: top of stack */
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/* rbx: data stack */
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@ -10,40 +11,6 @@
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/* r14: opcode shift register */
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/* r15: memory */
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.section ".note.openbsd.ident", "a"
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.p2align 2
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.long 0x8
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.long 0x4
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.long 0x1
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.ascii "OpenBSD\0"
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.long 0x0
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.p2align 2
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.section ".openbsd.syscalls"
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.long rd0
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.long $5
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.long rd1
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.long $5
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.long rd2
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.long $6
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.long rd3
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.long $3
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.long rd4
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.long $4
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.long rd5
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.long $0xA6
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.long rd6
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.long $3
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.long rd6
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.long $4
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.long rd7
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.long $4
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.long rd8
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.long $3
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.long rd9
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.long $1
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.bss
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.align 8
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@ -78,24 +45,18 @@ io_table:
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.text
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rdonly: mov $5, %eax /* sys_open */
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xor %esi, %esi /* O_RDONLY */
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mov $0666, %edx
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rd0: syscall
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rdonly:
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mov $0, %esi /* O_RDONLY */
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call open
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mov %eax, %edi
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ret
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wronly: mov $5, %eax /* sys_open */
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wronly:
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mov $1, %esi /* O_WRONLY */
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mov $0666, %edx
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rd1: syscall
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call open
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mov %eax, %edi
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ret
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close: mov $6, %eax /* sys_close */
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rd2: syscall
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ret
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load_image:
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mov rom(%rip), %rdi
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call rdonly
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@ -103,8 +64,7 @@ load_image:
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jz 1f
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mov %r15, %rsi
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mov $65536 * 4, %edx
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mov $3, %eax /* sys_read */
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rd3: syscall
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call read
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call close
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xor %eax, %eax
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lea dstack-4(%rip), %rbx
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@ -120,28 +80,36 @@ save_image:
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jz 1f
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mov %r15, %rsi
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mov $65536 * 4, %edx
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mov $4, %eax
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rd4: syscall
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call write
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call close
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1: pop %rax
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ret
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block_common:
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mov $0xA6, %eax /* sys_lseek */
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mov (%rbx), %esi
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shl $12, %esi
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xor %edx, %edx /* SEEK_SET */
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rd5: syscall
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mov $3, %eax /* sys_read */
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or %r10b, %r10b
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jz 1f
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mov $4, %al /* sys_write */
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1: lea (%r15,%r8,4), %rsi
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mov $4096, %edx
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rd6: syscall
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mov -4(%rbx), %esi
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sub $8, %rbx
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ret
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block_read:
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mov (%rbx), %esi # Get the block number
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shl $12, %esi # Multiply by 4096 (block size)
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xor %edx, %edx # SEEK_SET
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mov %rax, %rdi # File descriptor (from %rax)
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call lseek # Call lseek
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mov $4096, %edx # Number of bytes to read
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lea (%r15, %r8, 4), %rsi # Buffer location
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call read # Call read
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mov -4(%rbx), %esi # Retrieve value from the stack
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sub $8, %rbx # Update the stack pointer
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ret
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block_write:
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mov (%rbx), %esi # Get the block number
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shl $12, %esi # Multiply by 4096 (block size)
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xor %edx, %edx # SEEK_SET
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mov %rax, %rdi # File descriptor (from %rax)
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call lseek # Call lseek
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mov $4096, %edx # Number of bytes to read
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lea (%r15, %r8, 4), %rsi # Buffer location
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call write
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mov -4(%rbx), %esi # Retrieve value from the stack
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sub $8, %rbx # Update the stack pointer
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ret
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.align 32
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table: ret
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@ -271,7 +239,7 @@ an: and (%rbx), %eax
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or: or (%rbx), %eax
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sub $4, %rbx
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ret
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.align 32
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.align 32
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xo: xor (%rbx), %eax
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sub $4, %rbx
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ret
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@ -324,48 +292,64 @@ io: mov %eax, %ecx
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1: ret
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ioa: push %rax
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mov $4, %eax /* sys_write */
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mov $1, %edi
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mov %rsp, %rsi
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mov $1, %edx
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rd7: syscall
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mov %rsp, %rsi /* buffer pointer */
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mov $1, %edx /* write one byte */
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mov $1, %edi /* file descriptor (stdout) */
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call write
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pop %rax
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mov (%rbx), %eax
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sub $4, %rbx
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ret
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iob: add $4, %rbx
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xiob: add $4, %rbx
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mov %eax, (%rbx)
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mov $3, %eax /* sys_read */
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push %rax
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xor %edi, %edi
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mov %rsp, %rsi
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mov $1, %edx
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rd8: syscall
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xor %edi, %edi /* file descriptor (stdin) */
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mov %rsp, %rsi /* buffer pointer */
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mov $1, %edx /* read one byte */
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call read
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pop %rax
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ret
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iob: add $4, %rbx
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mov %eax, (%rbx)
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xor %edi, %edi # %edi = 0 (stdin)
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lea a(%rip), %rsi # Load address of 'a' into %rsi (buffer)
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mov $1, %edx # %edx = 1 (read one byte)
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call read # Call libc read: read(0, a, 1)
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movzx a(%rip), %eax # Move the byte from 'a' into %eax (zero-extend)
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ret
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ioc: mov %eax, %r8d
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mov blocks(%rip), %rdi
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call rdonly
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xor %r10d, %r10d
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call block_common
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mov $0, %rsi
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mov $0, %rdx
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call open /* open file (read-only) */
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call block_read
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call close
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mov %esi, %eax
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ret
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iod: mov %eax, %r8d
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mov blocks(%rip), %rdi
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call wronly
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mov $1, %r10b
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call block_common
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mov $1, %rsi
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mov $0, %rdx
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call open /* open file (write-only) */
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call block_write
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call close
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mov %esi, %eax
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ret
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ioe: jmp save_image
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iof: call load_image
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xor %rax, %rax
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xor %r13, %r13
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jmp _execute
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iog: mov $65536, %r13d
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ret
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ioh: add $8, %rbx
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mov %eax, -4(%rbx)
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lea astack-4(%rip), %rdx
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@ -377,7 +361,9 @@ ioh: add $8, %rbx
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shr $2, %eax
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ret
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_start: xor %eax, %eax
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main:
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xor %eax, %eax
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lea memory(%rip), %r15
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lea dstack-4(%rip), %rbx
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lea astack-4(%rip), %r12
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@ -434,6 +420,5 @@ _execute:
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1: inc %r13
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3: cmp $65536, %r13
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jl 2b
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mov $1, %eax /* sys_exit */
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xor %edi, %edi
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rd9: syscall
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call exit /* exit program */
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