[llvm] edfb2f8 - [yaml2obj] - Support the "Offset" key for the .dynsym section.

[Georgii Rymar via llvm-commits]

Author: Georgii Rymar
Date: 2020-10-28T14:22:29+03:00
New Revision: edfb2f8b235ff72f00375ae2424f7eb98da08234

URL: https://github.com/llvm/llvm-project/commit/edfb2f8b235ff72f00375ae2424f7eb98da08234
DIFF: https://github.com/llvm/llvm-project/commit/edfb2f8b235ff72f00375ae2424f7eb98da08234.diff

LOG: [yaml2obj] - Support the "Offset" key for the .dynsym section.

Our "implicit" sections are handled separately from regular ones.
It turns out that the "Offset" key is not handled properly for them.

Perhaps we can generalize handling in one place, but before doing that I'd like
to add support and test cases for each implicit section.
(I need this particular single change to unblock another patch that is already on review,
and I guess doing it independently for each section will be cleaner, see below).

In this patch I've removed `explicit-dynsym-no-dynstr.yaml` to `dynsym-section.yaml`
and added the new test into. In a follow-up we probably might want
to merge 2 another existent `dynsymtab-*.yaml` tests into it too.

Differential revision: https://reviews.llvm.org/D90224

Added: 
    llvm/test/tools/yaml2obj/ELF/dynsym-section.yaml

Modified: 
    llvm/lib/ObjectYAML/ELFEmitter.cpp

Removed: 
    llvm/test/tools/yaml2obj/ELF/explicit-dynsym-no-dynstr.yaml


################################################################################
diff  --git a/llvm/lib/ObjectYAML/ELFEmitter.cpp b/llvm/lib/ObjectYAML/ELFEmitter.cpp
index b811ccec06a3..cbd76c7aad1b 100644
--- a/llvm/lib/ObjectYAML/ELFEmitter.cpp
+++ b/llvm/lib/ObjectYAML/ELFEmitter.cpp
@@ -903,7 +903,8 @@ void ELFState<ELFT>::initSymtabSectionHeader(Elf_Shdr &SHeader,
 
   assignSectionAddress(SHeader, YAMLSec);
 
-  SHeader.sh_offset = alignToOffset(CBA, SHeader.sh_addralign, /*Offset=*/None);
+  SHeader.sh_offset =
+      alignToOffset(CBA, SHeader.sh_addralign, RawSec ? RawSec->Offset : None);
 
   if (RawSec && (RawSec->Content || RawSec->Size)) {
     assert(Symbols.empty());

diff  --git a/llvm/test/tools/yaml2obj/ELF/dynsym-section.yaml b/llvm/test/tools/yaml2obj/ELF/dynsym-section.yaml
new file mode 100644
index 000000000000..1c6f3efe3cfd
--- /dev/null
+++ b/llvm/test/tools/yaml2obj/ELF/dynsym-section.yaml
@@ -0,0 +1,33 @@
+## Check how we produce SHT_DYNSYM sections.
+
+## Check we do not crash/assert when .dynsym is specified
+## explicitly, but .dynstr is not present.
+## Check we set the sh_link field to 0 for the .dynsym section in this case.
+
+# RUN: yaml2obj %s -o %t1
+# RUN: llvm-readelf --section-headers %t1 | FileCheck %s
+
+# CHECK:      Section Headers:
+# CHECK-NEXT:  [Nr] Name    Type   Address          Off    Size   ES Flg Lk
+# CHECK-NEXT:  [ 0]         NULL   0000000000000000 000000 000000 00 0   0
+# CHECK-NEXT:  [ 1] .dynsym DYNSYM 0000000000000000 000040 000018 18 A   0
+
+--- !ELF
+FileHeader:
+  Class: ELFCLASS64
+  Data:  ELFDATA2LSB
+  Type:  ET_DYN
+Sections:
+  - Name:   .dynsym
+    Type:   SHT_DYNSYM
+    Offset: [[OFFSET=<none>]]
+
+## Check we can use the "Offset" key to to set an arbitrary offset for the SHT_DYNSYM section.
+
+# RUN: yaml2obj %s -DOFFSET=0x100 -o %t2
+# RUN: llvm-readelf --section-headers %t2 | FileCheck %s --check-prefix=OFFSET
+
+# OFFSET:      Section Headers:
+# OFFSET-NEXT:   [Nr] Name    Type   Address          Off    Size   ES Flg Lk Inf Al
+# OFFSET-NEXT:   [ 0]         NULL   0000000000000000 000000 000000 00     0   0  0
+# OFFSET-NEXT:   [ 1] .dynsym DYNSYM 0000000000000000 000100 000018 18   A 0   1  0

diff  --git a/llvm/test/tools/yaml2obj/ELF/explicit-dynsym-no-dynstr.yaml b/llvm/test/tools/yaml2obj/ELF/explicit-dynsym-no-dynstr.yaml
deleted file mode 100644
index 31977643bd61..000000000000
--- a/llvm/test/tools/yaml2obj/ELF/explicit-dynsym-no-dynstr.yaml
+++ /dev/null
@@ -1,21 +0,0 @@
-## Check we do not crash/assert when .dynsym is specified
-## explicitly, but .dynstr is not present.
-
-# RUN: yaml2obj %s -o %t
-# RUN: llvm-readelf --section-headers %t | FileCheck %s
-
-## Check that .dynsym has Link field set to 0.
-
-# CHECK:      Section Headers:
-# CHECK-NEXT:  [Nr] Name    Type   Address          Off    Size   ES Flg Lk
-# CHECK-NEXT:  [ 0]         NULL   0000000000000000 000000 000000 00 0   0
-# CHECK-NEXT:  [ 1] .dynsym DYNSYM 0000000000000000 000040 000018 18 A   0
-
---- !ELF
-FileHeader:
-  Class: ELFCLASS64
-  Data:  ELFDATA2LSB
-  Type:  ET_DYN
-Sections:
-  - Name: .dynsym
-    Type: SHT_DYNSYM