make dlerror produce informative results

note that dlerror is specified to be non-thread-safe, so no locking is
performed on the error flag or message aside from the rwlock already
held by dlopen or dlsym. if 2 invocations of dlsym are generating
errors at the same time, they could clobber each other's results, but
the resulting string, albeit corrupt, will still be null-terminated.
any use of dlerror in such a situation could not be expected to give
meaningful results anyway.

diff --git a/src/ldso/dynlink.c b/src/ldso/dynlink.c
index e0013ec0eecfe698dd717135e79cb55b44214e78..0533bbb2c3811aca2126ac1d336aca34309d03e7 100644 (file)
--- a/src/ldso/dynlink.c
+++ b/src/ldso/dynlink.c
@@ -18,6 +18,7 @@
 #include <dlfcn.h>
 
 static int errflag;
+static char errbuf[128];
 
 #ifdef __PIC__
 
@@ -142,8 +143,11 @@ static void do_relocs(unsigned char *base, size_t *rel, size_t rel_size, size_t
                        ctx = IS_COPY(type) ? dso->next : dso;
                        sym_val = (size_t)find_sym(ctx, name, IS_PLT(type));
                        if (!sym_val && sym->st_info>>4 != STB_WEAK) {
+                               snprintf(errbuf, sizeof errbuf,
+                                       "Error relocating %s: %s: symbol not found",
+                                       dso->name, name);
                                if (runtime) longjmp(rtld_fail, 1);
-                               dprintf(2, "%s: symbol not found\n", name);
+                               dprintf(2, "%s\n", errbuf);
                                _exit(127);
                        }
                        sym_size = sym->st_size;
@@ -405,9 +409,11 @@ static void load_deps(struct dso *p)
                        if (p->dynv[i] != DT_NEEDED) continue;
                        dep = load_library(p->strings + p->dynv[i+1]);
                        if (!dep) {
-                               if (runtime) longjmp(rtld_fail, 1);
-                               dprintf(2, "%s: %m (needed by %s)\n",
+                               snprintf(errbuf, sizeof errbuf,
+                                       "Error loading shared library %s: %m (needed by %s)",
                                        p->strings + p->dynv[i+1], p->name);
+                               if (runtime) longjmp(rtld_fail, 1);
+                               dprintf(2, "%s\n", errbuf);
                                _exit(127);
                        }
                        if (runtime) {
@@ -634,9 +640,13 @@ void *dlopen(const char *file, int mode)
                tail = orig_tail;
                tail->next = 0;
                p = 0;
+               errflag = 1;
+               goto end;
        } else p = load_library(file);
 
        if (!p) {
+               snprintf(errbuf, sizeof errbuf,
+                       "Error loading shared library %s: %m", file);
                errflag = 1;
                goto end;
        }
@@ -694,6 +704,7 @@ static void *do_dlsym(struct dso *p, const char *s, void *ra)
                        return p->deps[i]->base + sym->st_value;
        }
        errflag = 1;
+       snprintf(errbuf, sizeof errbuf, "Symbol not found: %s", s);
        return 0;
 }
 
@@ -720,7 +731,7 @@ char *dlerror()
 {
        if (!errflag) return 0;
        errflag = 0;
-       return "unknown error";
+       return errbuf;
 }
 
 int dlclose(void *p)