[PATCH]mips: ldso: dlopen with flag RTLD_NOW should look up the symbols

[Andrew Bennett]

Hi Jean,

Many thanks for the patch.  If my reading of your patch is correct it looks as if it 
will not respect lazy function binding, as it always resolves the function entries.  You 
will therefore need to predicate this to happen only if RTLD_NOW is used.  

Having saying this I am not sure if the fix is in the correct place.  The issue here
is about how the dynamic loader loads different types of ELF files and then deals with 
resolving the ELF's symbols.  I would therefore be happier if the fix was made to the 
core dynamic loader code to handle this case.

Finally, it would be good if your testcase could be added to the tests in tests/dlopen 
so that we can check for this issue in the future.

Many thanks,


Andrew



From: Jean Lee [mailto:xiaoyur347 at gmail.com] 
Sent: 16 March 2015 07:37
To: Bernhard Reutner-Fischer
Cc: Andrew Bennett; Florian Fainelli; Gregory Fong; uclibc
Subject: Re: [PATCH]mips: ldso: dlopen with flag RTLD_NOW should look up the symbols

After reading eglibc code, I find it's much similar to uclibc ldso/ldso/mips/elfinterp.c:_dl_perform_mips_global_got_relocations.
See "http://www.eglibc.org/svn/branches/eglibc-2_18/libc/ports/sysdeps/mips/dl-machine.h" elf_machine_got_rel function for more inspect.
I slightly modify my last patch to speed the fixup function. 
Last patch: Go through the whole symtab.
This patch: Go through symtab[tpnt->dynamic_info[DT_MIPS_GOTSYM_IDX], the last item of symtab]. Actually this is the .got section. And .got section is subset of symtab.



 [PATCH] MIPS: Scan the symtab for the dependency of the library to
 avoid runtime empty function pointer. The dependency =
 SHN_UNDEF && STB_GLOBAL && (STT_FUNC || STT_OBJECT)


Signed-off-by: Jean Lee <xiaoyur347 at gmail.com>
---
 ldso/ldso/mips/elfinterp.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/ldso/ldso/mips/elfinterp.c b/ldso/ldso/mips/elfinterp.c
index dfe37c5..a83da8d 100644
--- a/ldso/ldso/mips/elfinterp.c
+++ b/ldso/ldso/mips/elfinterp.c
@@ -162,6 +162,7 @@ int _dl_parse_relocation_information(struct dyn_elf *xpnt,
 #endif
 
 	struct symbol_ref sym_ref;
+	ElfW(Sym) *psym = NULL;
 	/* Now parse the relocation information */
 	rel_size = rel_size / sizeof(ElfW(Rel));
 	rpnt = (ELF_RELOC *) rel_addr;
@@ -170,6 +171,33 @@ int _dl_parse_relocation_information(struct dyn_elf *xpnt,
 	strtab = (char *) tpnt->dynamic_info[DT_STRTAB];
 	got = (unsigned long *) tpnt->dynamic_info[DT_PLTGOT];
 
+	i = tpnt->dynamic_info[DT_MIPS_SYMTABNO_IDX] -
+		tpnt->dynamic_info[DT_MIPS_GOTSYM_IDX];
+	psym = symtab + tpnt->dynamic_info[DT_MIPS_GOTSYM_IDX];
+	for (; i != 0; --i, ++psym) {
+		if (psym->st_name == 0) {
+			continue;
+		}
+
+		if (psym->st_shndx != SHN_UNDEF
+			|| ELF_ST_BIND(psym->st_info) != STB_GLOBAL
+			|| (ELF_ST_TYPE(psym->st_info) != STT_FUNC
+				&& ELF_ST_TYPE(psym->st_info) != STT_OBJECT)) {
+			continue003B
+		}
+		symname = strtab + psym->st_name;
+		
+		sym_ref.tpnt = NULL;
+		sym_ref.sym = psym;
+		symbol_addr = (unsigned long)_dl_find_hash(symname,
+								scope,
+								tpnt,
+								ELF_RTYPE_CLASS_PLT, &sym_ref);
+		if (symbol_addr == 0) {
+			_dl_dprintf (2, "%s: undefined symbol: %s\n",tpnt->libname, symname);
+			return 1;
+		}
+	}
 
 	for (i = 0; i < rel_size; i++, rpnt++) {
 		reloc_addr = (unsigned long *) (tpnt->loadaddr +