Re: [patch][gold] Don't put rodata and text in the same segment.

[Rafael Espindola <espindola at google dot com>]

> I think it would be OK to have an option to put read-only data in a
> different segment.

I see. The attached patch moves the it behind an option.

2010-09-01  Rafael Espindola  <espindola@google.com>

	* layout.cc (Layout::attach_allocated_section_to_segment): Add support
	for --rosegment.
	(Layout::find_first_load_seg): Search all segments to find the first
	one.
	(Layout::set_segment_offsets): Align the address of a read only segment
	that follows a read only one.
	* Makefile.am: Add a --rosegment bootstrap test.
	* Makefile.in: Regenerate.
	* options.h (rosegment): New.

> Ian
>

Cheers,
-- 
Rafael Ãvila de EspÃndola

diff --git a/gold/Makefile.am b/gold/Makefile.am
index df5e66c..5f366b4 100644
--- a/gold/Makefile.am
+++ b/gold/Makefile.am
@@ -219,6 +219,7 @@ gcctestdir1/ld: ld-new
 	rm -f gcctestdir1/ld
 	(cd gcctestdir1 && $(LN_S) ../ld-new ld)
 
+# regular bootstrap
 ld1_SOURCES = $(sources_var)
 ld1_DEPENDENCIES = $(deps_var) gcctestdir1/ld
 ld1_LDADD = $(ldadd_var)
@@ -240,6 +241,29 @@ bootstrap-test: ld2
 	echo "cmp ld1 ld2" > $@
 	chmod +x $@
 
+# --rosegment bootstrap
+ld1_ro_SOURCES = $(sources_var)
+ld1_ro_DEPENDENCIES = $(deps_var) gcctestdir1/ld
+ld1_ro_LDADD = $(ldadd_var)
+ld1_ro_LDFLAGS = -Bgcctestdir1/ -Wl,--rosegment
+
+gcctestdir2-ro/ld: ld1-ro
+	test -d gcctestdir2-ro || mkdir -p gcctestdir2-ro
+	rm -f gcctestdir2/ld-ro
+	(cd gcctestdir2-ro && $(LN_S) ../ld1-ro ld)
+
+ld2_ro_SOURCES = $(sources_var)
+ld2_ro_DEPENDENCIES = $(deps_var) gcctestdir2-ro/ld
+ld2_ro_LDADD = $(ldadd_var)
+ld2_ro_LDFLAGS = -Bgcctestdir2-ro/ -Wl,--rosegment
+
+bootstrap-test-ro: ld2-ro
+	rm -f $@
+	echo "#!/bin/sh" > $@
+	echo "cmp ld1-ro ld2-ro" > $@
+	chmod +x $@
+
+# -r bootstrap
 libgold-1-r.o: gcctestdir1/ld libgold.a
 	gcctestdir1/ld -o $@ -r --whole-archive libgold.a
 
@@ -267,8 +291,8 @@ bootstrap-test-r: ld2-r
 	echo "cmp ld1-r ld2-r" > $@
 	chmod +x $@
 
-check_PROGRAMS = ld1 ld2 ld1-r ld2-r
-TESTS = bootstrap-test bootstrap-test-r
+check_PROGRAMS = ld1 ld2 ld1-r ld2-r ld1-ro ld2-ro
+TESTS = bootstrap-test bootstrap-test-r bootstrap-test-ro
 
 endif
 endif
diff --git a/gold/layout.cc b/gold/layout.cc
index 5edba48..81e15a4 100644
--- a/gold/layout.cc
+++ b/gold/layout.cc
@@ -1166,10 +1166,11 @@ Layout::attach_allocated_section_to_segment(Output_section* os)
   bool is_address_set = parameters->options().section_start(os->name(), &addr);
 
   // In general the only thing we really care about for PT_LOAD
-  // segments is whether or not they are writable, so that is how we
-  // search for them.  Large data sections also go into their own
-  // PT_LOAD segment.  People who need segments sorted on some other
-  // basis will have to use a linker script.
+  // segments is whether or not they are writable or executable,
+  // so that is how we search for them.
+  // Large data sections also go into their own PT_LOAD segment.
+  // People who need segments sorted on some other basis will
+  // have to use a linker script.
 
   Segment_list::const_iterator p;
   for (p = this->segment_list_.begin();
@@ -1181,6 +1182,9 @@ Layout::attach_allocated_section_to_segment(Output_section* os)
       if (!parameters->options().omagic()
 	  && ((*p)->flags() & elfcpp::PF_W) != (seg_flags & elfcpp::PF_W))
 	continue;
+      if (parameters->options().rosegment()
+          && ((*p)->flags() & elfcpp::PF_X) != (seg_flags & elfcpp::PF_X))
+        continue;
       // If -Tbss was specified, we need to separate the data and BSS
       // segments.
       if (parameters->options().user_set_Tbss())
@@ -1449,6 +1453,7 @@ Layout::define_group_signatures(Symbol_table* symtab)
 Output_segment*
 Layout::find_first_load_seg()
 {
+  Output_segment* best = NULL;
   for (Segment_list::const_iterator p = this->segment_list_.begin();
        p != this->segment_list_.end();
        ++p)
@@ -1457,8 +1462,13 @@ Layout::find_first_load_seg()
 	  && ((*p)->flags() & elfcpp::PF_R) != 0
 	  && (parameters->options().omagic()
 	      || ((*p)->flags() & elfcpp::PF_W) == 0))
-	return *p;
+        {
+          if (best == NULL || this->segment_precedes(*p, best))
+            best = *p;
+        }
     }
+  if (best != NULL)
+    return best;
 
   gold_assert(!this->script_options_->saw_phdrs_clause());
 
@@ -2616,13 +2626,22 @@ Layout::set_segment_offsets(const Target* target, Output_segment* load_seg,
 	      // page in the file, but the loader will put them on
 	      // different pages in memory.
 
+	      // If both the last segment and this one are readonly,
+	      // align so that the dynamic linker will not overlap
+	      // them in memory.
+
 	      addr = align_address(addr, (*p)->maximum_alignment());
 	      aligned_addr = addr;
 
-	      if (was_readonly && ((*p)->flags() & elfcpp::PF_W) != 0)
+	      if (was_readonly)
 		{
-		  if ((addr & (abi_pagesize - 1)) != 0)
-		    addr = addr + abi_pagesize;
+		  if (((*p)->flags() & elfcpp::PF_W) != 0)
+		    {
+		      if ((addr & (abi_pagesize - 1)) != 0)
+			addr = addr + abi_pagesize;
+		    }
+		  else
+		    addr = align_address(addr, abi_pagesize);
 		}
 
 	      off = orig_off + ((addr - orig_addr) & (abi_pagesize - 1));
diff --git a/gold/options.h b/gold/options.h
index c5e24cc..4e4730b 100644
--- a/gold/options.h
+++ b/gold/options.h
@@ -808,6 +808,10 @@ class General_options
               N_(" Only search directories specified on the command line."),
               NULL);
 
+  DEFINE_bool(rosegment, options::TWO_DASHES, '\0', false,
+              N_(" Use a distinct segment for ro but not executable sections."),
+              NULL);
+
   DEFINE_string(m, options::EXACTLY_ONE_DASH, 'm', "",
                 N_("Ignored for compatibility"), N_("EMULATION"));