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I was having trouble with the linker for the embedded arm gcc compiler, and I found a tutorial somewhere online saying that I could fix my linker errors in arm-none-eabi-gcc by including the argument -specs=nosys.specs, which worked for me, and it was able to compile my code.

My chip is an ATSAM7SE256 microcontroller, which to my understanding is an arm7tdmi processor using the armv4t and thumb instruction sets, and I've been compiling my code using:

arm-none-eabi-gcc -march=armv4t -mtune=arm7tdmi -specs=nosys.specs -o <exe_name>.elf <input_files>

And the code compiles with no issue, but I have no idea if it's doing what I think it's doing.

What is the significance of a spec file? What other values can you set with -specs=, and in what situations would you want to? Is nosys.specs the value I want for a completely embedded arm microcontroller?

Willis Hershey
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    Knowing what the linker errors were would be useful so that others might know when the solution is appropriate. A link to the "tutorial somewhere" would make this less vague too. – Clifford Jun 11 '21 at 17:43

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It is documented at: https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Overall-Options.html#Overall-Options

It is a file containing switches to override standard defaults for various build components such as the compiler, assembler and linker. For example it can be used to replace the default C library.

I have never seen it used; typically bare-metal embedded system builds explicitly specify --nostdlib then explicitly link the required library. It could be used for environment specific build environments to link other default code such as an RTOS I guess. Personally I'd rather make all that explicit on the command line that hiding it in a file somewhere.

Essentially it applies the switches specified in the file as if they were defaults, so can be used to define defaults for specific build and execution environments.

The format of the specs file is documented at https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Spec-Files.html#Spec-Files

Without seeing both the linker errors and the content of the nosys.specs file in this case it is difficult to say how or why it solved your linker problem. The alternative solution of course would be to apply whatever switches are in the specs file directly.

Clifford
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