When libexec/rtld-elf/rtld.c is compiled with clang, the r_debug_state()

function (a hook necessary for gdb support), is inlined, but since the
function contains no code, no calls to it are generated.  When gdb is
debugging a dynamically linked program, this causes backtraces to be
corrupted.

Fix it by marking the function __noinline, and inserting an empty asm
statement, that pretends to clobber memory.  This forces the compiler to
emit calls to r_debug_state() throughout rtld.c.

Approved by:	re (kib)

1 files changed, 9 insertions, 1 deletions

diff --git a/libexec/rtld-elf/rtld.c b/libexec/rtld-elf/rtld.c
index 0f5aabae734a..874f4bc61ffd 100644
--- a/libexec/rtld-elf/rtld.c
+++ b/libexec/rtld-elf/rtld.c
@@ -144,7 +144,7 @@ static void ld_utrace_log(int, void *, void *, size_t, int, const char *);
 static void rtld_fill_dl_phdr_info(const Obj_Entry *obj,
     struct dl_phdr_info *phdr_info);
 
-void r_debug_state(struct r_debug *, struct link_map *);
+void r_debug_state(struct r_debug *, struct link_map *) __noinline;
 
 /*
  * Data declarations.
@@ -2782,6 +2782,14 @@ linkmap_delete(Obj_Entry *obj)
 void
 r_debug_state(struct r_debug* rd, struct link_map *m)
 {
+    /*
+     * The following is a hack to force the compiler to emit calls to
+     * this function, even when optimizing.  If the function is empty,
+     * the compiler is not obliged to emit any code for calls to it,
+     * even when marked __noinline.  However, gdb depends on those
+     * calls being made.
+     */
+    __asm __volatile("" : : : "memory");
 }
 
 /*