C sum example

examples/C/sum/Makefile

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+TARGET = sum
+
+$(TARGET).objdump: $(TARGET)
+	riscv64-unknown-elf-objdump -S $(TARGET) > $(TARGET).objdump
+    
+$(TARGET): $(TARGET).c Makefile
+	riscv64-unknown-elf-gcc -o $(TARGET) -g -O \
+	  -march=rv64gc -mabi=lp64d -mcmodel=medany \
+	  -nostartfiles -T../common/test.ld -I../common \
+	  $(TARGET).c ../common/crt.S ../common/syscalls.c
+# Compiler flags:
+#  -o $(TARGET) defines the name of the output file
+#  -g generates debugging symbols for gdb
+#  -O turns on basic optimization
+#  -march=rv64gc -mabi=lp64d =mcmodel=medany generates code for RV64GC with doubles and long/ptrs = 64 bits
+#  -nostartfiles avoids inserting standard startup files because we are using crt.s
+#  -T specifies the linker file
+#  -I specifies the include path (e.g. for util.h)
+#  The last line defines the C files to compile.  
+#    crt.S is needed as our startup file to initialize the processor
+#    syscalls.c implements printf through the HTIF for Spike
+# other flags from riscv-tests makefiles that don't seem to be important
+#	  -ffast-math -DPREALLOCATE=1 -std=gnu99 -fno-tree-loop-distribute-patterns 
+#     -fno-common -static  -fno-builtin-printf -nostdlib -lm -lgcc 
+
+clean:
+	rm -f $(TARGET) $(TARGET).objdump

examples/C/sum/sum.c

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+// sum.C
+// David_Harris@hmc.edu 24 December 2021
+// Simple illustration of compiling C code
+
+#include <stdio.h>  // supports printf
+#include "util.h"   // supports verify
+
+long sum(long N) {
+  long result, i;
+   result = 0;
+   for (i=1; i<=N; i++) {
+       result = result + i;
+   }
+   return result;
+}
+
+int main(void) {
+    int s[1], expected[1];
+    s[0] = sum(4);
+    printf("s = %d\n", s[0]);
+    expected[0] = 10;
+    return verify(1, s, expected); // 0 means success
+}