Text relocations in PIEs

[Joseph S. Myers]

If uClibc's ld.so encounters text relocations in a shared library - one 
containing an object built without -fpic/-fPIC - then:

* If __FORCE_SHAREABLE_TEXT_SEGMENTS__, then it gives an error "Can't 
modify %s's text section. Use GCC option -fPIC for shared objects, 
please.\n" and exits.

* Otherwise, it makes the library's pages writable and relocates it.

If it encounters text relocations in a position-independent executable - 
one containing an object built without -fpie/-fPIE/-fpic/-fPIC - then:

* If __FORCE_SHAREABLE_TEXT_SEGMENTS__, it does nothing about making the 
pages writable, leading to a crash.

* Otherwise, the loop to make the pages writable uses the same variable 
ppnt as used in an outer loop, messing up that outer loop and also causing 
a crash.

This patch fixes both cases, by giving an error if 
__FORCE_SHAREABLE_TEXT_SEGMENTS__ and saving and restoring ppnt otherwise.  
Tested in both cases on ARM EABI.

Index: ldso/ldso/ldso.c
===================================================================
--- ldso/ldso/ldso.c	(revision 20342)
+++ ldso/ldso/ldso.c	(working copy)
@@ -286,6 +286,7 @@
 			_dl_debug_early("calling mprotect on the application program\n");
 			/* Now cover the application program. */
 			if (app_tpnt->dynamic_info[DT_TEXTREL]) {
+				ElfW(Phdr) *ppnt_outer = ppnt;
 				ppnt = (ElfW(Phdr) *) auxvt[AT_PHDR].a_un.a_val;
 				for (i = 0; i < auxvt[AT_PHNUM].a_un.a_val; i++, ppnt++) {
 					if (ppnt->p_type == PT_LOAD && !(ppnt->p_flags & PF_W))
@@ -294,7 +295,13 @@
 							     (unsigned long) ppnt->p_filesz,
 							     PROT_READ | PROT_WRITE | PROT_EXEC);
 				}
+				ppnt = ppnt_outer;
 			}
+#else
+			if (app_tpnt->dynamic_info[DT_TEXTREL]) {
+				_dl_dprintf(_dl_debug_file, "Can't modify application's text section; use the GCC option -fPIE for position-independent executables.\n");
+				_dl_exit(1);
+			}
 #endif
 
 #ifndef ALLOW_ZERO_PLTGOT

-- 
Joseph S. Myers
joseph at codesourcery.com