ldso/mips: dlsym() incorrectly matches undefined symbols

check_match() relies on checking for (sym->st_value == 0) to see if the
symbol is undefined.  This works reasonably well on most architectures,
such as ARM or i386:

$ readelf -s /lib32/libcap.so.2 | grep -E "\<malloc\>"
    17: 00000000     0 FUNC    GLOBAL DEFAULT  UND malloc@GLIBC_2.0 (2)

However, on MIPS, libbfd puts nonzero data in the st_value field to
facilitate resetting the symbol's GOT entry if the library that defines
the symbol gets unloaded:

$ mipsel-linux-readelf -s libfoo.so | grep -E "\<malloc\>"
    74: 00003140     0 FUNC    GLOBAL DEFAULT  UND malloc

This can cause check_match to report a false positive when examining the
external symbol reference.  Consequently dlsym() will return a bad pointer
to the caller.

Use the special MIPS logic from glibc-ports-2.13 to avoid this situation.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Signed-off-by: Carmelo Amoroso <carmelo.amoroso@st.com>

ldso/ldso/dl-hash.c

@@ -187,6 +187,10 @@ check_match (const ElfW(Sym) *sym, char *strtab, const char* undef_name, int typ
 		 * code/data definitions
 		 */
 		return NULL;
+#endif
+#ifdef ARCH_SKIP_RELOC
+	if (ARCH_SKIP_RELOC(type_class, sym))
+		return NULL;
 #endif
 	if (_dl_strcmp(strtab + sym->st_name, undef_name) != 0)
 		return NULL;

ldso/ldso/mips/dl-sysdep.h

@@ -113,6 +113,9 @@ else if ((dpnt->d_tag == DT_MIPS_RLD_MAP) && (dpnt->d_un.d_ptr)) \
      *(ElfW(Addr) *)(dpnt->d_un.d_ptr) =  (ElfW(Addr)) debug_addr; \
 } while (0)
 
+#define ARCH_SKIP_RELOC(type_class, sym) \
+     ((sym)->st_shndx == SHN_UNDEF && !((sym)->st_other & STO_MIPS_PLT))
+
 /* Initialization sequence for the application/library GOT.  */
 #define INIT_GOT(GOT_BASE,MODULE)						\
 do {										\