tccelf: consider DSO symbols for PROVIDE

An input shared object can be the only place where a conventional boundary name is referenced or defined. In that case the regular symbol table has no entry, but native ELF linkers still synthesize the executable definition so that it participates in dynamic symbol resolution.

Consult the input dynamic symbol table before treating a plain boundary name as unreferenced. Exercise the case with a DSO-defined end symbol whose address must be interposed by the executable's final boundary.

tccelf.c

@@ -1586,9 +1586,13 @@ static void provide_linker_sym(TCCState *s1, const char *name,
 {
     int sym_index = find_elf_sym(symtab_section, name);
 
-    if (!sym_index
-        || ((ElfW(Sym) *)symtab_section->data)[sym_index].st_shndx != SHN_UNDEF)
+    if (sym_index) {
+        if (((ElfW(Sym) *)symtab_section->data)[sym_index].st_shndx != SHN_UNDEF)
+            return;
+    } else if (!s1->dynsymtab_section
+               || !find_elf_sym(s1->dynsymtab_section, name)) {
         return;
+    }
     set_linker_sym(s1, name, sec, offs);
 }
 

tests/tests2/151+_dso_linker_symbol.c

@@ -0,0 +1,6 @@
+char end = 7;
+
+char *get_dso_end(void)
+{
+    return &end;
+}

tests/tests2/151_dso_linker_symbol.c

@@ -0,0 +1,12 @@
+#include <stdio.h>
+
+extern char _end[];
+extern char *get_dso_end(void);
+
+int main(void)
+{
+    int errors = get_dso_end() != _end;
+
+    printf("DSO linker symbol errors: %d\n", errors);
+    return errors;
+}

tests/tests2/151_dso_linker_symbol.expect

@@ -0,0 +1 @@
+DSO linker symbol errors: 0

tests/tests2/Makefile

@@ -38,7 +38,7 @@ ifeq ($(CONFIG_bcheck),no)
 endif
 ifeq ($(CONFIG_dll),no)
  SKIP += 113_btdll.test 147_def_library.test # no shared lib support yet
- SKIP += 149_end_copy_reloc.test
+ SKIP += 149_end_copy_reloc.test 151_dso_linker_symbol.test
 endif
 ifeq (-$(findstring gcc,$(CC))-,--)
  SKIP += $(patsubst %.expect,%.test,$(GEN-ALWAYS))
@@ -56,7 +56,7 @@ ifeq (-$(CONFIG_WIN32)-,-yes-)
  SKIP += 124_atomic_counter.test # No pthread support
  SKIP += 144_tls.test 146_tls_extern.test # TLS runtime not supported
  SKIP += 148_linker_symbols.test 149_end_copy_reloc.test # ELF linker tests
- SKIP += 150_linker_boundaries.test
+ SKIP += 150_linker_boundaries.test 151_dso_linker_symbol.test
 endif
 ifneq (,$(filter OpenBSD FreeBSD NetBSD,$(TARGETOS)))
  SKIP += 106_versym.test # no pthread_condattr_setpshared
@@ -70,7 +70,7 @@ endif
 ifeq ($(CONFIG_OSX),yes)
  SKIP += 144_tls.test 146_tls_extern.test # TLS runtime not supported on Mach-O
  SKIP += 148_linker_symbols.test 149_end_copy_reloc.test # ELF linker tests
- SKIP += 150_linker_boundaries.test
+ SKIP += 150_linker_boundaries.test 151_dso_linker_symbol.test
 endif
 ifeq ($(CONFIG_pie),yes)
  SKIP += 149_end_copy_reloc.test # PIE executables do not use copy relocations
@@ -183,6 +183,15 @@ GEN-ALWAYS =
 	./$(basename $@).exe \
     )
 
+# A linker symbol needed only by a DSO must be provided by the executable.
+151_dso_linker_symbol.test: NORUN = true
+151_dso_linker_symbol.test: T1 = ( \
+	$(TCC) -shared $(subst 151,151+,$1) -o 151_dso_linker_symbol$(DLLSUF) && \
+	$(TCC) $1 ./151_dso_linker_symbol$(DLLSUF) -Wl,-rpath=. \
+		-o $(basename $@).exe && \
+	./$(basename $@).exe \
+    )
+
 112_backtrace.test: FLAGS += -dt -b
 112_backtrace.test 113_btdll.test 126_bound_global.test: FILTER += \
     -e 's;[0-9A-Fa-fx]\{5,\};........;g' \