Add DW_AT_comp_dir to elf files.

This commit adds the compilation directory debug information for ELF files.
This feature helps debuggers locate the source file when debugging.
The feature is already present for Mach-O files.

Signed-off-by: Marco Vanotti <mvanotti@dc.uba.ar>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

output/outelf.c

@@ -84,6 +84,7 @@ static struct hash_table section_by_name;
 static struct elf_symbol *fwds;
 
 static char elf_module[FILENAME_MAX];
+static char elf_dir[FILENAME_MAX];
 
 extern const struct ofmt of_elf32;
 extern const struct ofmt of_elf64;
@@ -552,8 +553,10 @@ static void elf_init(void)
         ".shstrtab", ".strtab", ".symtab", ".symtab_shndx", NULL
     };
     const char * const *p;
+    const char * cur_path = nasm_realpath(inname);
 
     strlcpy(elf_module, inname, sizeof(elf_module));
+    strlcpy(elf_dir, nasm_dirname(cur_path), sizeof(elf_dir));
     sects = NULL;
     nsects = sectlen = 0;
     syms = saa_init((int32_t)sizeof(struct elf_symbol));
@@ -3307,7 +3310,8 @@ static void dwarf_generate(void)
         saa_write32(pinforel, (dwarf_linesym << 8) +  R_386_32); /* reloc to line */
         saa_write32(pinforel, 0);
         saa_write32(pinfo,0);       /* DW_AT_stmt_list */
-        saa_wbytes(pinfo, elf_module, strlen(elf_module)+1);
+        saa_wbytes(pinfo, elf_module, strlen(elf_module)+1); /* DW_AT_name */
+        saa_wbytes(pinfo, elf_dir, strlen(elf_dir)+1); /* DW_AT_comp_dir */
         saa_wbytes(pinfo, nasm_signature(), nasm_signature_len()+1);
         saa_write16(pinfo,DW_LANG_Mips_Assembler);
         saa_write8(pinfo,2);        /* abbrviation number LEB128u */
@@ -3346,7 +3350,8 @@ static void dwarf_generate(void)
         saa_write32(pinforel, (dwarf_linesym << 8) + R_X86_64_32); /* reloc to line */
         saa_write32(pinforel, 0);
         saa_write32(pinfo,0);			/* DW_AT_stmt_list */
-        saa_wbytes(pinfo, elf_module, strlen(elf_module)+1);
+        saa_wbytes(pinfo, elf_module, strlen(elf_module)+1); /* DW_AT_name */
+        saa_wbytes(pinfo, elf_dir, strlen(elf_dir)+1); /* DW_AT_comp_dir */
         saa_wbytes(pinfo, nasm_signature(), nasm_signature_len()+1);
         saa_write16(pinfo,DW_LANG_Mips_Assembler);
         saa_write8(pinfo,2);			/* abbrviation number LEB128u */
@@ -3386,7 +3391,8 @@ static void dwarf_generate(void)
         saa_write64(pinforel, (dwarf_linesym << 32) +  R_X86_64_32); /* reloc to line */
         saa_write64(pinforel, 0);
         saa_write32(pinfo,0);			/* DW_AT_stmt_list */
-        saa_wbytes(pinfo, elf_module, strlen(elf_module)+1);
+        saa_wbytes(pinfo, elf_module, strlen(elf_module)+1); /* DW_AT_name */
+        saa_wbytes(pinfo, elf_dir, strlen(elf_dir)+1); /* DW_AT_comp_dir */
         saa_wbytes(pinfo, nasm_signature(), nasm_signature_len()+1);
         saa_write16(pinfo,DW_LANG_Mips_Assembler);
         saa_write8(pinfo,2);			/* abbrviation number LEB128u */
@@ -3424,6 +3430,8 @@ static void dwarf_generate(void)
     saa_write8(pabbrev,DW_FORM_data4);
     saa_write8(pabbrev,DW_AT_name);
     saa_write8(pabbrev,DW_FORM_string);
+    saa_write8(pabbrev,DW_AT_comp_dir);
+    saa_write8(pabbrev,DW_FORM_string);
     saa_write8(pabbrev,DW_AT_producer);
     saa_write8(pabbrev,DW_FORM_string);
     saa_write8(pabbrev,DW_AT_language);