[ELF] Test case for correct input section order, when sections are listed in linker script

[evgeny777]

Summary

Current version does not maintain correct input section order, when sections are listed in linker script. Input sections always have the same order as in object files, which is not correct.
Consider this linker script

SECTIONS {
  .foo { *(.foo.*) *(.bar.*) }
}

The result ELF image should have all .foo.* sections placed before all .bar.* sections. This patch implements this adding order value to SectionRule and then sorting input sections properly in case ScriptConfig->DoLayout is true

[ruiu]

Currently we are creating output sections only in Writer.cpp, but George is working on doing it in LinkerScript.cpp if a linker script is given. If the logic is in LinkerScript.cpp, we can create output sections as we visit each SECTIONS subcommand in linker scripts, so we don't need to ask about it to getOutputSections. Therefore, I think you want to wait for that change.

[evgeny777]

Okay, great. Is someone working on symbol assignment within input section list? If not, I'd like to implement this.

[ruiu]

Is it different from your http://reviews.llvm.org/D22088?

[evgeny777]

Yes it is. I'd like to be able to do this:

SECTIONS {
    .foo : { *(.foo.*) end_foo = .; *(.bar.*) end_bar=.; } }
}

[ruiu]

I think no one is working on it, but I guess it also depends on the
George's work, as it can be done as we visit each SECTIONS command. If it
is not, feel free to write a patch.

[evgeny777]

Input section order problem was fixed by
https://reviews.llvm.org/D22455
and
https://reviews.llvm.org/D22617

This patch adds test case, so it won't be broken occasionally

[ruiu]

LGTM. Please update the commit message as this change now contains only a test.

test/ELF/linkerscript-input-order.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+
+# This test case should place input sections in script order: 
+# .foo.1 .foo.2 .bar.1 .bar.2
+# RUN: echo "SECTIONS { . = 0x1000; .foo : {*(.foo.*) *(.bar.*)  } }" > %t.script
+# RUN: ld.lld -o %t1 --script %t.script %t
+# RUN: llvm-objdump -section=.foo -s %t1 | FileCheck --check-prefix=SCRIPT_ORDER %s
+# SCRIPT_ORDER: Contents of section .foo:
+# SCRIPT_ORDER-NEXT: 1000 00000000 00000000 ffffffff eeeeeeee
+
+# This test case should place input sections in native order:
+# .bar.1 .foo.1 .bar.2 .foo.2
+# RUN: echo "SECTIONS { . = 0x1000; .foo : {*(.foo.* .bar.*)} }" > %t.script
+# RUN: ld.lld -o %t1 --script %t.script %t
+# RUN: llvm-objdump -section=.foo -s %t1 | FileCheck --check-prefix=FILE_ORDER %s
+# FILE_ORDER: Contents of section .foo:
+# FILE_ORDER-NEXT: 1000 ffffffff 00000000 eeeeeeee 00000000
+
+.global _start
+_start:
+ nop
+
+.section .bar.1,"a"
+bar1:
+ .long 0xFFFFFFFF
+
+.section .foo.1,"a"
+foo1:
+ .long 0
+
+.section .bar.2,"a"
+bar2:
+ .long 0xEEEEEEEE
+
+.section .foo.2,"a"
+foo2:
+ .long 0