fix 879 - support for --gc-sections

- pin .deh_eh and .minfo by emitting fake references in dso startup code

- enable --gc-sections linker switch

src/backend/elfobj.c

@@ -2673,8 +2673,6 @@ static size_t writeaddrval(int targseg, size_t offset, targ_size_t val, size_t s
 size_t ElfObj::writerel(int targseg, size_t offset, unsigned reltype,
                         IDXSYM symidx, targ_size_t val)
 {
-    assert(reltype != R_X86_64_NONE);
-
     size_t sz;
     if (I64)
     {
@@ -3164,7 +3162,7 @@ static void obj_rtinit()
 {
 #if TX86
     // create brackets for .deh_eh and .minfo sections
-    IDXSYM deh_beg, deh_end, minfo_beg, minfo_end, dso_rec;
+    IDXSYM deh_beg, deh, deh_end, minfo_beg, minfo, minfo_end, dso_rec;
     IDXSTR namidx;
     int seg;
 
@@ -3174,7 +3172,8 @@ static void obj_rtinit()
     seg = ElfObj::getsegment(".deh_beg", NULL, SHT_PROGDEF, shf_flags, NPTRSIZE);
     deh_beg = MAP_SEG2SYMIDX(seg);
 
-    ElfObj::getsegment(".deh_eh", NULL, SHT_PROGDEF, shf_flags, NPTRSIZE);
+    seg = ElfObj::getsegment(".deh_eh", NULL, SHT_PROGDEF, shf_flags, NPTRSIZE);
+    deh = MAP_SEG2SYMIDX(seg);
 
     seg = ElfObj::getsegment(".deh_end", NULL, SHT_PROGDEF, shf_flags, NPTRSIZE);
     deh_end = MAP_SEG2SYMIDX(seg);
@@ -3183,7 +3182,8 @@ static void obj_rtinit()
     seg = ElfObj::getsegment(".minfo_beg", NULL, SHT_PROGDEF, shf_flags, NPTRSIZE);
     minfo_beg = MAP_SEG2SYMIDX(seg);
 
-    ElfObj::getsegment(".minfo", NULL, SHT_PROGDEF, shf_flags, NPTRSIZE);
+    seg = ElfObj::getsegment(".minfo", NULL, SHT_PROGDEF, shf_flags, NPTRSIZE);
+    minfo = MAP_SEG2SYMIDX(seg);
 
     seg = ElfObj::getsegment(".minfo_end", NULL, SHT_PROGDEF, shf_flags, NPTRSIZE);
     minfo_end = MAP_SEG2SYMIDX(seg);
@@ -3444,6 +3444,12 @@ static void obj_rtinit()
         // ret
         buf->writeByte(0xC3);
         off += 2;
+
+        // add fake references to pin .minfo and .deh_eh sections (--gc-sections)
+        reltype = I64 ? R_X86_64_NONE : RI_TYPE_NONE;
+        off += ElfObj::writerel(codseg, off, reltype, minfo, 0);
+        off += ElfObj::writerel(codseg, off, reltype, deh, 0);
+
         Offset(codseg) = off;
 
         // put a reference into .ctors/.dtors each

src/link.c

@@ -555,21 +555,21 @@ int runLINK()
         argv.push(global.params.mapfile);
     }
 
-    if (0 && global.params.exefile)
-    {
-        /* This switch enables what is known as 'smart linking'
-         * in the Windows world, where unreferenced sections
-         * are removed from the executable. It eliminates unreferenced
-         * functions, essentially making a 'library' out of a module.
-         * Although it is documented to work with ld version 2.13,
-         * in practice it does not, but just seems to be ignored.
-         * Thomas Kuehne has verified that it works with ld 2.16.1.
-         * BUG: disabled because it causes exception handling to fail
-         * because EH sections are "unreferenced" and elided
-         */
-        argv.push("-Xlinker");
-        argv.push("--gc-sections");
-    }
+    /* This switch enables what is known as 'smart linking'
+     * in the Windows world, where unreferenced sections
+     * are removed from the executable. It eliminates unreferenced
+     * functions, essentially making a 'library' out of a module.
+     * Although it is documented to work with ld version 2.13,
+     * in practice it does not, but just seems to be ignored.
+     * Thomas Kuehne has verified that it works with ld 2.16.1.
+     */
+#if __linux__
+    /* Only works on linux because the linkers shipped with other
+     * OSes don't yet support this flag.
+     */
+    argv.push("-Xlinker");
+    argv.push("--gc-sections");
+#endif
 
     for (size_t i = 0; i < global.params.linkswitches->dim; i++)
     {   const char *p = (*global.params.linkswitches)[i];