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[PATCH] gold: Fix segfault on sparc with STT_SPARC_REGISTER and --gc-sections


gold/
 * symtab.cc (Symbol_table::add_from_relobj): Handle NULL symbols,
 which will be present for STT_SPARC_REGISTER.
 (Symbol_table::add_from_pluginobj): Likewise.
 (Symbol_table::add_from_dynobj): Likewise.
 (Symbol_table::add_from_incrobj): Removed dead code.
---

Easy reproduction:

    $ cat main.c
    int main() {
        return 0;
    }
    $ gcc -o main -Wl,--gc-sections main.c
    $ gcc -fuse-ld=gold -o main -Wl,--gc-sections main.c
    collect2: fatal error: ld terminated with signal 11 [Segmentation fault]
    compilation terminated.

This is because res->is_externally_visible inside Symbol_table::add_from_relobj
when res is NULL (since this is an STT_SPARC_REGISTER dummy symbol).

With this patch I've done the obvious bare minimum to get this to work, but
given these NULLs are floating around now I highly suspect there will be other
places where they crop up.

 gold/symtab.cc | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/gold/symtab.cc b/gold/symtab.cc
index 5ce5c31..b31794a 100644
--- a/gold/symtab.cc
+++ b/gold/symtab.cc
@@ -1325,6 +1325,9 @@ Symbol_table::add_from_relobj(
       res = this->add_from_object(relobj, name, name_key, ver, ver_key,
 				  is_default_version, *psym, st_shndx,
 				  is_ordinary, orig_st_shndx);
+
+      if (res == NULL)
+	continue;
       
       if (is_forced_local)
 	this->force_local(res);
@@ -1406,6 +1409,9 @@ Symbol_table::add_from_pluginobj(
 		              is_default_version, *sym, st_shndx,
 			      is_ordinary, st_shndx);
 
+  if (res == NULL)
+    return NULL;
+
   if (is_forced_local)
     this->force_local(res);
 
@@ -1602,6 +1608,9 @@ Symbol_table::add_from_dynobj(
 	    }
 	}
 
+      if (res == NULL)
+	continue;
+
       // Note that it is possible that RES was overridden by an
       // earlier object, in which case it can't be aliased here.
       if (st_shndx != elfcpp::SHN_UNDEF
@@ -1640,7 +1649,6 @@ Symbol_table::add_from_incrobj(
 
   Stringpool::Key ver_key = 0;
   bool is_default_version = false;
-  bool is_forced_local = false;
 
   Stringpool::Key name_key;
   name = this->namepool_.add(name, true, &name_key);
@@ -1650,9 +1658,6 @@ Symbol_table::add_from_incrobj(
 		              is_default_version, *sym, st_shndx,
 			      is_ordinary, st_shndx);
 
-  if (is_forced_local)
-    this->force_local(res);
-
   return res;
 }
 
-- 
2.9.1


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