[Tinycc-devel] tcc --emit-relocs

[Barath Aron]

Hi,

The OS that I use loads all executable to random addresses and relocates 
them. There are a few reasons behind this, and it isn't important. 
Executables built with gcc works fine if the "-Wl,--emit-relocs" is 
passed. TCC compiles a good relocatable ELF, except it removes the 
relocation entries related to the data section.
For instance, if the program contains some stuff like this:

char* my_str = "Hello!";

will crash at runtime due to the totally different addresses stored in 
the data section and in the reality. For example, the ELF could be 
loaded at 0x10001AA0000 or at 0x10003F40000. The actual load address is 
unknown at compile time for sure.

I have a hack that allows to keep the data relocations I want, but I'm 
pretty sure the patch won't work for all the cases. I'm was in a rush to 
make tcc work on the OS I use, so here it is [1] (in svn diff format).

Can you help me with? :)

Áron



 [1]:


Index: libtcc.c
===================================================================
--- libtcc.c    (revision 22252)
+++ libtcc.c    (working copy)
@@ -1439,6 +1439,8 @@
             ignoring = 1;
         } else if (link_option(option, "O", &p)) {
             ignoring = 1;
+        } else if (link_option(option, "q", &p) || link_option(option, 
"emit-relocs", &p)) {
+            s->emit_relocs = 1;
         } else if (link_option(option, "rpath=", &p)) {
             s->rpath = copy_linker_arg(p);
         } else if (link_option(option, "section-alignment=", &p)) {
Index: tcc.h
===================================================================
--- tcc.h    (revision 22252)
+++ tcc.h    (working copy)
@@ -600,6 +600,7 @@
     int rdynamic; /* if true, all symbols are exported */
     int symbolic; /* if true, resolve symbols in the current module 
first */
     int alacarte_link; /* if true, only link in referenced objects 
from archive */
+    int emit_relocs; /* if true, leave relocation sections and contets 
in fully linked executables (ELF only) */

     char *tcc_lib_path; /* CONFIG_TCCDIR or -B option */
     char *soname; /* as specified on the command line (-soname) */
Index: tccelf.c
===================================================================
--- tccelf.c    (revision 22252)
+++ tccelf.c    (working copy)
@@ -48,6 +48,8 @@

 ST_FUNC void tccelf_new(TCCState *s)
 {
+    int symtab_sh_flags = 0;
+
     /* no section zero */
     dynarray_add((void ***)&s->sections, &s->nb_sections, NULL);

@@ -57,7 +59,9 @@
     bss_section = new_section(s, ".bss", SHT_NOBITS, SHF_ALLOC | 
SHF_WRITE);

     /* symbols are always generated for linking stage */
-    symtab_section = new_symtab(s, ".symtab", SHT_SYMTAB, 0,
+    if(s->emit_relocs)
+        symtab_sh_flags |= SHF_ALLOC;
+    symtab_section = new_symtab(s, ".symtab", SHT_SYMTAB, symtab_sh_flags,
                                 ".strtab",
                                 ".hashtab", SHF_PRIVATE);
     strtab_section = symtab_section->link;
@@ -787,10 +791,10 @@
         tgt += rel->r_addend;
 #endif
         addr = s->sh_addr + rel->r_offset;
-    relocate(s1, rel, type, ptr, addr, tgt);
+        relocate(s1, rel, type, ptr, addr, tgt);
     }
     /* if the relocation is allocated, we change its symbol table */
-    if (sr->sh_flags & SHF_ALLOC)
+    if (!s->emit_relocs && (sr->sh_flags & SHF_ALLOC))
         sr->link = s1->dynsym;
 }