3 files changed, 177 insertions, 0 deletions
diff --git a/README.md b/README.md
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+++ b/README.md
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+# minias
+
+An assembler for elf x86_64, written for fun and learning.
+
+Goals:
+
+- Assemble the output of [cproc](https://github.com/michaelforney/cproc)/[qbe](https://c9x.me/compile/).
+- x86_64 elf output.
+- Static linking.
+- A simple, tiny, fast implementation (in that order).
+
+Stretch goals:
+
+- Assemble what is needed to compile musl libc.
+- Dynamic linking.
+
+Non Goals:
+
+- Assemble every assembly instruction.
+- Work as a library.
+
+# Resources
+
+- [goas](https://github.com/DQNEO/goas)
+- [neatas](https://repo.or.cz/neatas.git)
+\ No newline at end of file
diff --git a/main.c b/main.c
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+++ b/main.c
@@ -0,0 +1,119 @@
+#include "minias.h"
+
+typedef struct {
+  Elf64_Shdr hdr;
+  size_t capacity;
+  uint8_t *data;
+} Section;
+
+#define MAXSECTIONS 32
+static Section sections[MAXSECTIONS];
+static size_t nsections = 0;
+
+static Section *strtab = NULL;
+static Section *symtab = NULL;
+static Section *textsec = NULL;
+
+void secappend(Section *s, uint8_t *bytes, size_t n) {
+  while (s->capacity < s->hdr.sh_size + n) {
+    s->capacity = s->capacity * 2;
+    s->data = xrealloc(s->data, s->capacity);
+  }
+  memcpy(s->data + s->hdr.sh_size, bytes, n);
+  s->hdr.sh_size += n;
+}
+
+Elf64_Word elfstr(const char *s) {
+  Elf64_Word i;
+  for (i = 0; i < strtab->hdr.sh_size; i++) {
+    if (i == 0 || (strtab->data[i - 1] == 0))
+      if (strcmp(s, (char *)&strtab->data[i]) == 0)
+        return i;
+  }
+  secappend(strtab, (uint8_t *)s, strlen(s) + 1);
+  return i;
+}
+
+Section *newsection(const char *name) {
+  Section *s;
+  s = &sections[nsections++];
+  if (nsections > MAXSECTIONS)
+    die("too many sections");
+  s->hdr.sh_name = elfstr(name);
+  s->capacity = 16;
+  s->data = xmalloc(s->capacity);
+  return s;
+}
+
+void initsections(void) {
+  /* Manually init string table */
+  strtab = &sections[nsections++];
+  strtab->hdr.sh_type = SHT_STRTAB;
+  strtab->capacity = 16;
+  strtab->data = xmalloc(strtab->capacity);
+  strtab->hdr.sh_name = elfstr(".strtab");
+  strtab->hdr.sh_entsize = 1;
+
+  symtab = newsection(".symtab");
+  symtab->hdr.sh_type = SHT_SYMTAB;
+  symtab->hdr.sh_link = 1;
+  symtab->hdr.sh_entsize = sizeof(Elf64_Sym);
+
+  textsec = newsection(".text");
+  textsec->hdr.sh_type = SHT_PROGBITS;
+  textsec->hdr.sh_flags = SHF_EXECINSTR | SHF_ALLOC;
+  textsec->hdr.sh_entsize = 1;
+}
+
+void out(uint8_t *buf, size_t n) {
+  if (write(STDOUT_FILENO, buf, n) != n)
+    die("io error");
+}
+
+void outelf(void) {
+  size_t i;
+  uint64_t offset = 0;
+  Elf64_Ehdr ehdr = {0};
+
+  ehdr.e_ident[0] = 0x7f;
+  ehdr.e_ident[1] = 'E';
+  ehdr.e_ident[2] = 'L';
+  ehdr.e_ident[3] = 'F';
+  ehdr.e_ident[4] = ELFCLASS64;
+  ehdr.e_ident[5] = ELFDATA2LSB;
+  ehdr.e_ident[6] = 1;
+  ehdr.e_type = ET_REL;
+  ehdr.e_machine = EM_X86_64;
+  ehdr.e_flags = 0;
+  ehdr.e_version = 1;
+  ehdr.e_ehsize = sizeof(Elf64_Ehdr);
+  ehdr.e_shentsize = sizeof(Elf64_Shdr);
+  ehdr.e_shoff = sizeof(Elf64_Ehdr);
+  ehdr.e_shnum = nsections;
+  ehdr.e_shstrndx = 1;
+  offset = sizeof(Elf64_Shdr) * nsections;
+  /*
+  textsec->shdr.sh_offset = offset;
+  textsec->shdr.sh_size = 0;
+  offset += textsec->shdr.sh_size * textsec->shdr.sh_entsize;
+  symstrsec->shdr.sh_size = 0;
+  symstrsec->shdr.sh_offset = offset;
+  offset += symstrsec->shdr.sh_size * symstrsec->shdr.sh_entsize;
+  */
+
+  out((uint8_t *)&ehdr, sizeof(ehdr));
+  for (i = 0; i < nsections; i++) {
+    sections[i].hdr.sh_offset = offset;
+    out((uint8_t *)&sections[i].hdr, sizeof(Elf64_Shdr));
+    offset += sections[i].hdr.sh_size;
+  }
+  for (i = 0; i < nsections; i++) {
+    out(sections[i].data, sections[i].hdr.sh_size);
+  }
+}
+
+int main() {
+  initsections();
+  outelf();
+  return 0;
+}
+\ No newline at end of file
diff --git a/minias.h b/minias.h
new file mode 100644
index 0000000..f694f79
--- /dev/null
+++ b/minias.h
@@ -0,0 +1,33 @@
+#include <elf.h>
+#include <stddef.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+static void die(char *s) {
+  write(STDERR_FILENO, s, strlen(s));
+  exit(1);
+}
+
+static void *xcalloc(size_t nmemb, size_t n) {
+  void *p;
+  p = calloc(nmemb, n);
+  if (!p)
+    die("out of memory");
+  return p;
+}
+
+static void *xmalloc(size_t n) {
+  void *p;
+  p = malloc(n);
+  if (!p)
+    die("out of memory");
+  return p;
+}
+
+static void *xrealloc(void *p, size_t n) {
+  p = realloc(p, n);
+  if (!p)
+    die("out of memory");
+  return p;
+}
+\ No newline at end of file