ARM GCC Linker flags to use external newlib libraries?

Question

I have been trying to link separate libraries that I've built from newlib to a pre-built package of ARM GCC 12, which I got from their developer site. I've rebuilt newlib using modified flags gotten from the file in ARM GCC 12.2.mpacbti-rel1-x86_64-arm-none-eabi-manifest.txt. Specifically I removed the --enable-newlib-mb flag as it causes a lot of extra build space to be generated. I have ran several builds of newlib and have verified that the newlib configuration flags being used do not affect the errors being produced.

Using the compilation flag '-nostdlib', which from my knowledge is necessary to use external libraries instead of the default ones, results in some undefined references to C library functions. Some of these include 'memcpy', 'memset' or 'malloc'.

The current linker flags I've used for this are: -nostdlib -L[gcc path]/lib -lgcc -lc -lm

With the built newlib libraries being located in the [gcc-install]/lib directory. This currently causes the undefined references.

Edit: Compiler output contains undefined references to: 'memset', 'mktime' 'setvbuf', 'strlen', 'strcmp', 'memcpy', 'strftime', '__aeabi_dcmplt', '__aeabi_f2d', '__aeabi_dadd', '__aeabi_dmul, '__aeabi_d2ulz', 'memmove', 'modf', 'localtime_r', 'mallinfo', '_ctype_', 'gettimeofday', '_errno', 'malloc', and 'write'.

Answer 1

Using the flag -nostdlib caused linking errors due to the GCC not linking the startup file (as per KamilCuk's response). Omitting this flag and instead only using -L to provide the newlib library path solved the undefined function references.

Moreover, I had to spend some time resolving floating point ABI issues. The linker complained that my project's .elf file was using hardfp floating point ABI operations while my libraries were using softfp. I provided the following path for newlib, which solved the issue (version 4.3.0):

-L[path to newlib build]/arm-none-eabi/thumb/autofp/v7/fpu/newlib -lc