hi all;
i've make a small program in linux(asm source), i use syscall(int 0x80) in most case to IO program, but i can only used sys_write and sys_read, sys_lseek. a problem when i progress in file IO, i can know file size but don't know how to alloc memory, somebody can tell me how to do that

You can use libc from your source. You need to import needed functions from the dynamic libraries. (As a variant - you can compile to object file and then to link to the static c libraries).
You can download FreshLib sources from here
The documentation is published here
You can choose to use the FreshLib to access files as well as memory allocations - in result you will have portable application for Win32 and Linux.
On the other hand, you simply can use Linux import macros to import functions you need.

Regards

Since you seem to want to use syscalls exclusively, you may want to look at brk() and mmap() with the MAP_ANONYMOUS and MAP_PRIVATE flags.

Read this: http://x86asm.net/articles/memory-allocation-in-linux/index.html

thank for all