Lantronix EDS2100 Linux SDK - User Guide - Page 75

B. Differences between uClinux and Standard Linux

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B. Differences Between µClinux and Standard Linux The µClinux kernel is a collection of patches to make the standard Linux kernel run on CPUs that do not have an MMU. As a consequence you will encounter some differences between the µClinux and the standard Linux behavior. While porting existing Linux applications to µClinux/ColdFire you should be aware of these limitations:  no fork() - consider using vfork() instead but beware of the difference of their semantics  no daemon() - it is usually implemented on top of fork and cannot be easily replaced without changing the semantics.  fixed stack size -- the stack of an application is set at execution time and cannot grow during runtime. The default stack size is 4k! It can be increased with the "-s" option of m68k-uClinuxelf2flat.  limited libc compared to glibc -- either add more to libc, or remove some functionality.  no support for ELF binary file format  very limited support for shared libraries due to missing MMU -- all applications get linked statically  mmap() is very inefficient  no paging -- applications have to be loaded completely into RAM, the heap is very susceptible to fragmentation.  processes do not run in their isolated virtual memory -- they can corrupt other processes and even the kernel. Linux Software Developers Kit (SDK) User Guide 75

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Linux Software Developers Kit (SDK) User Guide
75
B. Differences Between μClinux and Standard
Linux
The µClinux kernel is a collection of patches to make the standard Linux kernel run on CPUs that
do not have an MMU. As a consequence you will encounter some differences between the
µClinux and the standard Linux behavior. While porting existing Linux applications to
µClinux/ColdFire you should be aware of these limitations:
no fork() – consider using vfork() instead but beware of the difference of their semantics
no daemon() – it is usually implemented on top of fork and cannot be easily replaced without
changing the semantics.
fixed stack size -- the stack of an application is set at execution time and cannot grow during
runtime. The default stack size is 4k! It can be increased with the "-s" option of m68k-uClinux-
elf2flat.
limited libc compared to glibc -- either add more to libc, or remove some functionality.
no support for ELF binary file format
very limited support for shared libraries due to missing MMU -- all applications get linked
statically
mmap() is very inefficient
no paging -- applications have to be loaded completely into RAM, the heap is very
susceptible to fragmentation.
processes do not run in their isolated virtual memory -- they can corrupt other processes and
even the kernel.