align segments

masm/asm.c

@@ -17,6 +17,8 @@ extern char *current_file;
 #define SYMSEC_STUB -1
 #define SYMSEC_EXTERN -1
 
+#define SEC_ALIGN 0x1000
+
 static int create_symbol(struct assembler *assembler,
 			 const char name[MAX_LEX_LENGTH],
 			 ssize_t section_idx,
@@ -338,7 +340,7 @@ static int assemble_phdr(struct assembler *assembler, Elf32_Phdr **res,
 		hdr->p_paddr = 0;
 		hdr->p_filesz = htonl(size);
 		hdr->p_memsz = htonl(size);
-		hdr->p_align = htonl(0x1000);
+		hdr->p_align = htonl(SEC_ALIGN);
 	}
 
 	*res = phdr;
@@ -530,17 +532,30 @@ static void update_offsets(struct assembler *assembler, Elf32_Ehdr *ehdr)
 		ptr += len * sizeof(Elf32_Rela);
 	}
 
+	// section padding
+	{
+		uint32_t mod = ptr % SEC_ALIGN;
+		if (mod != 0)
+			assembler->secalign = (SEC_ALIGN - mod);
+		else
+			assembler->secalign = 0;
+		ptr += assembler->secalign;
+	}
+
 	// sections
+	size_t v_addr = 0x00400000;
 	for (uint32_t i = 0; i < assembler->sectab.len; i++) {
 		struct section *sec = &assembler->sectab.sections[i];
-		int idx = sec->shdr_idx;
+		uint32_t idx = sec->shdr_idx;
+		uint32_t size = ntohl(phdr[i].p_filesz);
 		phdr[i].p_offset = htonl(ptr);
-		phdr[i].p_vaddr = htonl(ptr);
-		phdr[i].p_paddr = htonl(ptr);
+		phdr[i].p_vaddr = htonl(v_addr);
+		phdr[i].p_paddr = htonl(v_addr);
 		shdr[idx].sh_offset = htonl(ptr);
 		shdr[idx].sh_size = phdr[i].p_filesz;
 		shdr[idx].sh_addr = phdr[i].p_vaddr;
-		ptr += ntohl(phdr[i].p_filesz);
+		v_addr += size;
+		ptr += size;
 	}
 
 	// symtab
@@ -567,8 +582,7 @@ static void update_offsets(struct assembler *assembler, Elf32_Ehdr *ehdr)
 
 static void update_sym_shindx(struct assembler *assembler)
 {
-	for (size_t i = 0; i < assembler->symtab.len; i++)
-	{
+	for (size_t i = 0; i < assembler->symtab.len; i++) {
 		Elf32_Sym *sym = &assembler->symtab.symbols[i];
 		ssize_t sec = assembler->symtab.sections[i];
 
@@ -605,6 +619,12 @@ static int write_file(struct assembler *assembler, Elf32_Ehdr *ehdr,
 		fwrite(ptr, sizeof(Elf32_Rela), len, out);
 	}
 
+	// section padding
+	for (uint32_t i = 0; i < assembler->secalign; i++) {
+		uint8_t zero = 0;
+		fwrite(&zero, 1, 1, out);
+	}
+
 	// sections
 	for (uint32_t i = 0; i < assembler->sectab.len; i++) {
 		struct section *sec = &assembler->sectab.sections[i];

masm/asm.h

@@ -213,6 +213,7 @@ struct assembler {
 
 	/// Segments
 	struct section_table sectab;
+	uint32_t secalign; // align sections to 0x1000 when writing
 
 	/// program header
 	Elf32_Phdr *phdr;

masm/test.asm

@@ -1,3 +1,8 @@
+.rodata
+gay:
+.word 3
+
+
 .data
 
 str: