[ELF] Support INSERT [AFTER|BEFORE] for orphan sections

D43468+D44380 added INSERT [AFTER|BEFORE] for non-orphan sections. This patch
makes INSERT work for orphan sections as well.

`SECTIONS {...} INSERT [AFTER|BEFORE] .foo` does not set `hasSectionCommands`, so the result
will be similar to a regular link without a linker script. The differences when `hasSectionCommands` is set include:

* image base is different
* -z noseparate-code/-z noseparate-loadable-segments are unavailable
* some special symbols such as `_end _etext _edata` are not defined

The behavior is similar to GNU ld:
INSERT is not considered an external linker script.

This feature makes the section layout more flexible. It can be used to:

* Place .nv_fatbin before other readonly SHT_PROGBITS sections to mitigate relocation overflows.
* Disturb the layout to expose address sensitive application bugs.

Reviewed By: grimar

Differential Revision: https://reviews.llvm.org/D74375

1 files changed, 32 insertions, 0 deletions

diff --git a/lld/test/ELF/linkerscript/insert-duplicate.test b/lld/test/ELF/linkerscript/insert-duplicate.test
new file mode 100644
index 0000000..8fa7e2c
--- /dev/null
+++ b/lld/test/ELF/linkerscript/insert-duplicate.test
@@ -0,0 +1,32 @@
+# REQUIRES: x86
+## Test that we can handle cases where an output section is specified by multiple
+## INSERT commands. Each output section description creates a new instance.
+## A redundant description matches no input sections and thus is a no-op.
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %p/Inputs/insert-after.s -o %t.o
+# RUN: ld.lld -T %s %t.o -o %t
+# RUN: llvm-readelf -S -l %t | FileCheck %s
+
+# CHECK:      Name      Type     Address          Off
+# CHECK-NEXT:           NULL     0000000000000000 000000
+# CHECK-NEXT: .text     PROGBITS 00000000002011c8 0001c8
+# CHECK-NEXT: .foo.data PROGBITS 00000000002021d0 0001d0
+# CHECK-NEXT: .foo.text PROGBITS 00000000002031d8 0001d8
+# CHECK:      Type
+# CHECK-NEXT: PHDR {{.*}} R
+# CHECK-NEXT: LOAD {{.*}} R
+# CHECK-NEXT: LOAD {{.*}} R E
+# CHECK-NEXT: LOAD {{.*}} RW
+# CHECK-NEXT: LOAD {{.*}} R E
+# CHECK-NEXT: LOAD {{.*}} RW
+# CHECK-NEXT: GNU_STACK {{.*}} RW
+
+## First, move .foo.data after .foo.text
+SECTIONS { .foo.data : { *(.foo.data) } } INSERT AFTER .foo.text;
+
+## Next, move .foo.text after .foo.data
+SECTIONS { .foo.text : { *(.foo.text) } } INSERT AFTER .foo.data;
+
+## No-op. The .foo.data output section is a different instance and matches no
+## input sections.
+SECTIONS { .foo.data : { *(.foo.data) } } INSERT AFTER .foo.text;