Allow for ELF files without program headers e.g. unlinked object files.

* Add more section types to prevent "unknown" from printing
* Add alloc, exec, and write flags of sections to output table

src/elfpatch.c

@@ -30,6 +30,19 @@
 #include <fort.h>
 #include <inttypes.h>
 #include <patchelfcrc/crc-output-struct.h>
+#include <byteswap.h>
+
+static const union  {
+	uint8_t data[4];
+	uint32_t val;
+} _endianess_check_union = {{1u, 2u, 3u, 4u}};
+
+enum endianess {
+	END_LITTLE = 0x04030201ul,
+	END_BIG = 0x01020304ul,
+};
+
+#define HOST_ENDIANESS (_endianess_check_union.value)
 
 struct elf_section {
 	GElf_Shdr section_header;
@@ -77,15 +90,16 @@ static uint32_t get_uint32_from_byte_string(const uint8_t *data, bool little_end
 	uint32_t out = 0ul;
 	int i;
 
+	/* Always shift in in big endian format */
 	for (i = 0; i < 4; i++) {
-		if (little_endian)
-			out >>= 8u;
-		else
 			out <<= 8u;
-
+		out |= (uint32_t)data[i];
-		out |= (((uint32_t)data[i]) << (little_endian ? 24u : 0u));
 	}
 
+	/* Swap bytes if little endian */
+	if (little_endian)
+		out = bswap_32(out);
+
 	return out;
 }
 
@@ -96,14 +110,12 @@ static void write_crc_to_byte_array(uint8_t *byte_array, uint32_t crc, uint8_t c
 	if (!byte_array)
 		return;
 
+	if (!little_endian)
+		crc = bswap_32(crc);
+
 	for (i = 0; i < crc_size_bytes; i++) {
-		if (little_endian) {
+		byte_array[i] = (uint8_t)(crc & 0xFFul);
-			byte_array[i] = (uint8_t)(crc & 0xFFul);
+		crc >>= 8u;
-			crc >>= 8u;
-		} else {
-			byte_array[i] = (uint8_t)((crc & 0xFF000000ul) >> 24u);
-			crc <<= 8u;
-		}
 	}
 }
 
@@ -136,6 +148,14 @@ static const char *section_type_to_str(Elf64_Word type)
 		return "INIT_ARRAY";
 	case SHT_FINI_ARRAY:
 		return "FINI_ARRAY";
+	case SHT_PREINIT_ARRAY:
+		return "PREINIT_ARRAY";
+	case SHT_DYNAMIC:
+		return "DYNAMIC";
+	case SHT_ARM_ATTRIBUTES:
+		return "ARM_ATTRIBUTES";
+	case SHT_ARM_PREEMPTMAP:
+		return "ARM_PREEMPTMAP";
 	default:
 		break;
 	}
@@ -147,6 +167,7 @@ static void print_sections(elfpatch_handle_t *ep)
 	SlList *iter;
 	ft_table_t *table;
 	const struct elf_section *section;
+	bool alloc, write, exec;
 
 	ret_if_ep_err(ep);
 
@@ -162,15 +183,23 @@ static void print_sections(elfpatch_handle_t *ep)
 
 	/* Write header */
 	ft_set_cell_prop(table, 0, FT_ANY_COLUMN, FT_CPROP_ROW_TYPE, FT_ROW_HEADER);
-	ft_write_ln(table, "Section", "Type", "Size", "VMA", "LMA", "File Offset");
+	ft_write_ln(table, "Section", "Type", "ALLOC", "WRITE", "EXEC", "Size", "VMA", "LMA", "File Offset");
 
 	for (iter = ep->sections; iter; iter = sl_list_next(iter)) {
 		section = (const struct elf_section *)iter->data;
 		if (!section)
 			continue;
-		ft_printf_ln(table, "%s|%s|%lu|%p|%p|%p",
+
+		alloc = !!(section->section_header.sh_flags & SHF_ALLOC);
+		write = !!(section->section_header.sh_flags & SHF_WRITE);
+		exec = !!(section->section_header.sh_flags & SHF_EXECINSTR);
+
+		ft_printf_ln(table, "%s|%s|%s|%s|%s|%lu|%p|%p|%p",
 			     section->name,
 			     section_type_to_str(section->section_header.sh_type),
+			     alloc ? "x" : "",
+			     write ? "x" : "",
+			     exec ? "x" : "",
 			     section->section_header.sh_size,
 			     (void *)section->section_header.sh_addr,
 			     (void *)section->lma,
@@ -261,6 +290,12 @@ static int elf_patch_read_program_headers(elfpatch_handle_t *ep)
 		return -1;
 	}
 
+	if (header_count == 0) {
+		/* No program headers found. This ELF file is probably not linked */
+		ep->program_headers_count = 0;
+		return 0;
+	}
+
 	ep->program_headers = (GElf_Phdr *)malloc(header_count * sizeof(GElf_Phdr));
 	if (!ep->program_headers) {
 		/* Mem error. Abort. Program will crash eventually */
@@ -306,9 +341,11 @@ static void resolve_section_lmas(elfpatch_handle_t *ep)
 		if (!sec)
 			continue;
 
+		/* By default each sections LMA is assumed to be its LMA as well */
+		sec->lma = (uint64_t)sec->section_header.sh_addr;
+
 		if (sec->section_header.sh_type == SHT_NOBITS) {
 			/* Section does not contain data. It may be allocated but is not loaded. Therefore, LMA=VMA. */
-			sec->lma = (uint64_t)sec->section_header.sh_addr;
 			continue;
 		}