Load ELF into emulator

.gitignore

@@ -1 +1,2 @@
 *.exe
+*.bin

build.bat

@@ -1,2 +1,6 @@
-clang main.c -o riscv.exe -std=c11
+clang emulator/main.c -o emulator.exe -std=c11 -D_CRT_SECURE_NO_WARNINGS
+REM clang linker/main.c -o linker.exe -std=c11 -D_CRT_SECURE_NO_WARNINGS
+
+clang --target=riscv32 -march=rv32i -e _main -nostdlib main.asm -o main.bin
+
 

emulator/main.c

@@ -3,6 +3,134 @@
 #include <inttypes.h>
 #include <assert.h>
 #include <stdbool.h>
+#include <string.h>
+
+#define ET_NONE 0x00
+#define ET_REL  0x01
+#define ET_EXEC 0x02
+#define ET_DYN  0x03
+#define ET_CORE 0x04
+
+struct Elf32Header
+{
+    uint8_t  ident[16];
+    uint16_t type;
+    uint16_t machine;
+    uint32_t version;
+    uint32_t entry;
+    uint32_t phoff;
+    uint32_t shoff;
+    uint32_t flags;
+    uint16_t ehsize;
+    uint16_t phentsize;
+    uint16_t phnum;
+    uint16_t shentsize;
+    uint16_t shnum;
+    uint16_t shstrndx;
+};
+
+#define PT_NULL    0x00000000
+#define PT_LOAD    0x00000001
+#define PT_DYNAMIC 0x00000002
+#define PT_INTERP  0x00000003
+#define PT_NOTE    0x00000004
+#define PT_SHLIB   0x00000005
+#define PT_PHDR    0x00000006
+#define PT_TLS     0x00000007
+
+#define PF_X 0x1
+#define PF_W 0x2
+#define PF_R 0x4
+
+struct Elf32ProgramHeader
+{
+    uint32_t type;
+    uint32_t offset;
+    uint32_t vaddr;
+    uint32_t paddr;
+    uint32_t filesz;
+    uint32_t memsz;
+    uint32_t flags;
+    uint32_t align;
+};
+
+bool load_elf(const char* file, char* mem, uint32_t mem_size, uint32_t* start_address)
+{
+    FILE* fp = fopen(file, "rb");
+    if (fp == NULL)
+    {
+        printf("Couldn't open input file\n");
+        return false;
+    }
+
+    struct Elf32Header header;
+    size_t read = fread(&header, sizeof(struct Elf32Header), 1, fp);
+    if (read != 1)
+    {
+        printf("ELF header too small\n");
+        return false;
+    }
+
+    static uint8_t kValidIdent[7] = {
+        0x7f, 0x45, 0x4c, 0x46,
+        1, 1, 1
+    };
+    if (memcmp(kValidIdent, header.ident, 7) != 0)
+    {
+        printf("Invalid ELF header\n");
+        return false;
+    }
+
+    if (header.type != ET_EXEC)
+    {
+        printf("Can only link EXEC ELF files\n");
+        return false;
+    }
+
+    memset(mem, 0, mem_size);
+    
+    assert(header.phnum == 0 || header.phentsize == sizeof(struct Elf32ProgramHeader));
+    for (uint32_t i = 0; i < header.phnum; ++i)
+    {
+        struct Elf32ProgramHeader pheader;
+
+        fseek(fp, header.phoff + i * header.phentsize, SEEK_SET);
+        read = fread(&pheader, sizeof(struct Elf32ProgramHeader), 1, fp);
+        if (read != 1)
+        {
+            printf("Error reading program header at index %u\n", i);
+            return false;
+        }
+
+        if (pheader.type == PT_LOAD)
+        {
+            if (pheader.paddr + pheader.memsz > mem_size)
+            {
+                printf("Memory not large enough for ELF file\n");
+                return false;
+            }
+
+            fseek(fp, pheader.offset, SEEK_SET);
+            read = fread(mem + pheader.paddr, pheader.filesz, 1, fp);
+            if (read != 1)
+            {
+                printf("Error when copying ELF segment\n");
+                return false;
+            }
+        }
+    }
+
+    if (header.entry > mem_size)
+    {
+        printf("Entry address out of bounds\n");
+        return false;
+    }
+
+    *start_address = header.entry;
+    fclose(fp);
+
+    return true;
+}
 
 inline uint32_t sign_extend(uint32_t word, uint32_t size)
 {
@@ -639,5 +767,34 @@ void test()
 int main(int argc, char* argv[])
 {
     test();
+
+    if (argc < 2)
+    {
+        printf("Usage: %s <input elf>\n", argv[0]);
+        return EXIT_FAILURE;
+    }
+
+    uint32_t mem_size = 16 * 1024 * 1024;
+    char* mem = (char*)malloc(mem_size);
+    uint32_t start_address = 0;
+
+    if (!load_elf(argv[1], mem, mem_size, &start_address))
+    {
+        printf("Error loading ELF into memory\n");
+        return EXIT_FAILURE;
+    }
+
+    struct Hart hart = {0};
+    hart.pc = start_address;
+
+    while (true)
+    {
+        uint32_t instruction = *(uint32_t*)(mem + hart.pc);
+        execute(&hart, instruction);
+        printf("pc=%x x1=%d x2=%d x3=%d x4=%d\n",
+            hart.pc, hart.regs[1], hart.regs[2], hart.regs[3], hart.regs[4]);
+        fgetc(stdout);
+    }
+    
     return EXIT_SUCCESS;
 }

main.asm

@@ -0,0 +1,9 @@
+.section .text
+.global _main
+_main:
+    li      x1, 5
+    addi    x2, x1, 45
+
+loop:
+    addi    x2, x2, 1
+    j       loop