Linker scripts and Section Reordering.
Sriraman Tallam
tmsriram@google.com
Wed Jan 9 23:40:00 GMT 2013
On Wed, Jan 9, 2013 at 3:22 PM, Ian Lance Taylor <iant@google.com> wrote:
> On Wed, Jan 9, 2013 at 2:46 PM, Sriraman Tallam <tmsriram@google.com> wrote:
>>
>> I moved this to Output_section_definition::set_section_addresses. I
>> dont think this is necessary in
>> Orphan_output_section::set_section_addresses for the following reason.
>> Orphan_output_sections are for those not seen in the linker script.
>> Such an output section is created for every input section that is not
>> caught in the linker script. Such input sections are not grouped by
>> prefix as the output_section_name method in script-sections.cc is used
>> to group them. So, these input sections cannot be handled by section
>> ordering.
It seems like this is needed in
Orphan_output_section::set_section_addresses too. I can have cases
where there are multiple input sections with the same name that are
not referenced by the linker script. They will all be grouped under
one Orphan_output_section and this can be reordered later. I have
attached the new patch with this correction. Sorry about the
confusion. I have attached the new patch. I duplicated the code in
set_section_addresses. I did not create a new function as only the
comments are long and repeating.
Thanks,
Sri
>
> This patch is OK.
>
> Thanks.
>
> Ian
-------------- next part --------------
* output.h (sort_attached_input_sections): Change to be public.
* script-sections.cc
(Output_section_definition::set_section_addresses): Sort
attached input sections according to section order before linker
script assigns section addresses.
(Orphan_output_section::set_section_addresses): Sort
attached input sections according to section order before linker
script assigns section addresses.
* Makefile.am (final_layout.sh): Use a simple linker script to
check if section ordering still works.
* Makefile.in: Regenerate.
Index: output.h
===================================================================
RCS file: /cvs/src/src/gold/output.h,v
retrieving revision 1.144
diff -u -u -p -r1.144 output.h
--- output.h 12 Dec 2012 03:41:40 -0000 1.144
+++ output.h 9 Jan 2013 23:35:57 -0000
@@ -3300,6 +3300,10 @@ class Output_section : public Output_dat
this->dynsym_index_ = index;
}
+ // Sort the attached input sections.
+ void
+ sort_attached_input_sections();
+
// Return whether the input sections sections attachd to this output
// section may require sorting. This is used to handle constructor
// priorities compatibly with GNU ld.
@@ -4253,10 +4257,6 @@ class Output_section : public Output_dat
add_output_merge_section(Output_section_data* posd, bool is_string,
uint64_t entsize);
- // Sort the attached input sections.
- void
- sort_attached_input_sections();
-
// Find the merge section into which an input section with index SHNDX in
// OBJECT has been added. Return NULL if none found.
Output_section_data*
Index: script-sections.cc
===================================================================
RCS file: /cvs/src/src/gold/script-sections.cc,v
retrieving revision 1.56
diff -u -u -p -r1.56 script-sections.cc
--- script-sections.cc 14 Aug 2012 08:31:56 -0000 1.56
+++ script-sections.cc 9 Jan 2013 23:35:57 -0000
@@ -2294,6 +2294,15 @@ Output_section_definition::set_section_a
uint64_t old_dot_value = *dot_value;
uint64_t old_load_address = *load_address;
+ // If input section sorting is requested via --section-ordering-file or
+ // linker plugins, then do it here. This is important because we want
+ // any sorting specified in the linker scripts, which will be done after
+ // this, to take precedence. The final order of input sections is then
+ // guaranteed to be according to the linker script specification.
+ if (this->output_section_ != NULL
+ && this->output_section_->input_section_order_specified())
+ this->output_section_->sort_attached_input_sections();
+
// Decide the start address for the section. The algorithm is:
// 1) If an address has been specified in a linker script, use that.
// 2) Otherwise if a memory region has been specified for the section,
@@ -2865,6 +2874,15 @@ Orphan_output_section::set_section_addre
uint64_t address = *dot_value;
address = align_address(address, this->os_->addralign());
+ // If input section sorting is requested via --section-ordering-file or
+ // linker plugins, then do it here. This is important because we want
+ // any sorting specified in the linker scripts, which will be done after
+ // this, to take precedence. The final order of input sections is then
+ // guaranteed to be according to the linker script specification.
+ if (this->os_ != NULL
+ && this->os_->input_section_order_specified())
+ this->os_->sort_attached_input_sections();
+
// For a relocatable link, all orphan sections are put at
// address 0. In general we expect all sections to be at
// address 0 for a relocatable link, but we permit the linker
Index: testsuite/Makefile.am
===================================================================
RCS file: /cvs/src/src/gold/testsuite/Makefile.am,v
retrieving revision 1.203
diff -u -u -p -r1.203 Makefile.am
--- testsuite/Makefile.am 4 Jan 2013 23:50:27 -0000 1.203
+++ testsuite/Makefile.am 9 Jan 2013 23:35:57 -0000
@@ -251,8 +251,10 @@ final_layout.o: final_layout.cc
$(CXXCOMPILE) -O0 -c -ffunction-sections -fdata-sections -g -o $@ $<
final_layout_sequence.txt:
(echo "*_Z3barv*" && echo ".text._Z3bazv" && echo "*_Z3foov*" && echo "*global_varb*" && echo "*global_vara*" && echo "*global_varc*") > final_layout_sequence.txt
-final_layout: final_layout.o final_layout_sequence.txt gcctestdir/ld
- $(CXXLINK) -Bgcctestdir/ -Wl,--section-ordering-file,final_layout_sequence.txt final_layout.o
+final_layout_script.lds:
+ (echo ""SECTIONS { .text : { *(.text*) } .bss : { *(.bss*) } }") > final_layout_script.lds
+final_layout: final_layout.o final_layout_sequence.txt final_layout_script.lds gcctestdir/ld
+ $(CXXLINK) -Bgcctestdir/ -Wl,--section-ordering-file,final_layout_sequence.txt -Wl,-T,final_layout_script.lds final_layout.o
final_layout.stdout: final_layout
$(TEST_NM) -n --synthetic final_layout > final_layout.stdout
Index: testsuite/Makefile.in
===================================================================
RCS file: /cvs/src/src/gold/testsuite/Makefile.in,v
retrieving revision 1.214
diff -u -u -p -r1.214 Makefile.in
--- testsuite/Makefile.in 4 Jan 2013 23:50:27 -0000 1.214
+++ testsuite/Makefile.in 9 Jan 2013 23:35:58 -0000
@@ -125,6 +125,7 @@ check_PROGRAMS = $(am__EXEEXT_1) $(am__E
@GCC_TRUE@@NATIVE_LINKER_TRUE@ icf_safe_test icf_safe_so_test \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ final_layout \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ final_layout_sequence.txt \
+@GCC_TRUE@@NATIVE_LINKER_TRUE@ final_layout_script.lds \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ text_section_grouping \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ icf_virtual_function_folding_test \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ icf_preemptible_functions_test \
@@ -4355,8 +4356,10 @@ uninstall-am:
@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(CXXCOMPILE) -O0 -c -ffunction-sections -fdata-sections -g -o $@ $<
@GCC_TRUE@@NATIVE_LINKER_TRUE@final_layout_sequence.txt:
@GCC_TRUE@@NATIVE_LINKER_TRUE@ (echo "*_Z3barv*" && echo ".text._Z3bazv" && echo "*_Z3foov*" && echo "*global_varb*" && echo "*global_vara*" && echo "*global_varc*") > final_layout_sequence.txt
-@GCC_TRUE@@NATIVE_LINKER_TRUE@final_layout: final_layout.o final_layout_sequence.txt gcctestdir/ld
-@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(CXXLINK) -Bgcctestdir/ -Wl,--section-ordering-file,final_layout_sequence.txt final_layout.o
+@GCC_TRUE@@NATIVE_LINKER_TRUE@final_layout_script.lds:
+@GCC_TRUE@@NATIVE_LINKER_TRUE@ (echo "SECTIONS { .text : { *(.text*) } .bss : { *(.bss*) } }") > final_layout_script.lds
+@GCC_TRUE@@NATIVE_LINKER_TRUE@final_layout: final_layout.o final_layout_sequence.txt final_layout_script.lds gcctestdir/ld
+@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(CXXLINK) -Bgcctestdir/ -Wl,--section-ordering-file,final_layout_sequence.txt -Wl,-T,final_layout_script.lds final_layout.o
@GCC_TRUE@@NATIVE_LINKER_TRUE@final_layout.stdout: final_layout
@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(TEST_NM) -n --synthetic final_layout > final_layout.stdout
@GCC_TRUE@@NATIVE_LINKER_TRUE@text_section_grouping.o: text_section_grouping.cc
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