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Diffstat (limited to 'snippets/allocate.s')
| -rw-r--r-- | snippets/allocate.s | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/snippets/allocate.s b/snippets/allocate.s new file mode 100644 index 0000000..ef80957 --- /dev/null +++ b/snippets/allocate.s @@ -0,0 +1,20 @@ +# void *allocate(int n) +# +# A naive memory allocator that simply retrieves some new space from the OS. +# It is not possible to deallocate the memory again. +.globl allocate +.type allocate, @function +allocate: + push %rdi + # 1. Find the current end of the data segment. + movq $12, %rax # brk + xorq %rdi, %rdi # 0 means we retrieve the current end. + syscall + # 2. Add the amount of memory we want to allocate. + pop %rdi # the argument + push %rax # current end, which is where the allocated memory will start + addq %rax, %rdi # compute the new end + movq $12, %rax # brk + syscall + pop %rax # the old end, which is the address of our allocated memory + ret |