How is this gcc instruction being interpreted?

I downloaded libopencm3 (https://github.com/libopencm3/libopencm3) library and compiled it. It worked. I found a small project that uses this library and copied the instructions from its makefile.

all:
arm-none-eabi-gcc \
    -Os \
    -ggdb3 \
    -mthumb \
    -mcpu=cortex-m0 \
    -msoft-float \
    -Wall \
    -Wextra \
    -Wundef \
    -Wshadow \
    -Wredundant-decls \
    -fno-common \
    -ffunction-sections \
    -fdata-sections \
    -std=c11 \
    -MD \
    -DSTM32F0 \
    -I./libopencm3/include \
    -o main.o \
    -c main.c

arm-none-eabi-gcc \
    --static \
    -nostartfiles \
    -Tstm32f0.ld \
    -mthumb \
    -mcpu=cortex-m0 \
    -msoft-float \
    -ggdb3 \
    -Wl,-Map=main.map \
    -Wl,--cref \
    -Wl,--gc-sections \
    -L./libopencm3/lib \
    main.o \
    -lopencm3_stm32f0 \
    -Wl,--start-group -lc -lgcc -lnosys -Wl,--end-group \
    -o main.elf

I created a folder for the project, pasted libopencm3 folder inside it and compiled. It’s working, but I don’t understand how this part works:

-L./libopencm3/lib main.o -lopencm3_stm32f0

If I am right, it is instructing to find opencm3_stm32f0 library inside /libopencm3/lib, but inside that folder I found libopencm3_stm32f0.a instead.

I want to know why they changed the name and omitted the extension and it still worked.

>Solution :

This isn’t related to makefiles or to any specific library, or to embedded systems, so those tags on your question are not needed.

If you look up the -l option in the documentation of the linker, you’ll understand how it works.