[llvm-objcopy]Allow llvm-objcopy to be used on an ELF file with no section headers

This patch fixes https://bugs.llvm.org/show_bug.cgi?id=41293 and
https://bugs.llvm.org/show_bug.cgi?id=41045. llvm-objcopy assumed that
it could always read a section header string table. This isn't the case
when the sections were previously all stripped, and the e_shstrndx field
was set to 0. This patch fixes this. It also fixes a double space in an
error message relating to this issue, and prevents llvm-objcopy from
adding extra space for non-existent section headers, meaning that
--strip-sections on the output of a previous --strip-sections run
produces identical output, simplifying the test.

Reviewed by: rupprecht, grimar

Differential Revision: https://reviews.llvm.org/D59989

llvm-svn: 357475

1 files changed, 26 insertions, 0 deletions

diff --git a/llvm/test/tools/llvm-objcopy/ELF/copy-after-strip-sections.test b/llvm/test/tools/llvm-objcopy/ELF/copy-after-strip-sections.test
new file mode 100644
index 00000000000..3b61649b263
--- /dev/null
+++ b/llvm/test/tools/llvm-objcopy/ELF/copy-after-strip-sections.test
@@ -0,0 +1,26 @@
+# llvm-objcopy's --strip-sections removes the section headers. It should be
+# possible to run the tool on the output after this operation. Performing any
+# subsequent stripping operation, or copying the object, should produce
+# identical output.
+
+# RUN: yaml2obj %s -o %t.in
+# RUN: llvm-objcopy %t.in %t.stripped --strip-sections
+# RUN: llvm-objcopy %t.stripped %t.stripped2 --strip-sections
+# RUN: llvm-objcopy %t.stripped2 %t.out
+# RUN: cmp %t.stripped %t.stripped2
+# RUN: cmp %t.stripped %t.out
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_EXEC
+  Machine: EM_X86_64
+Sections:
+  - Name: .text
+    Type: SHT_PROGBITS
+    Content: 'facefeed'
+ProgramHeaders:
+  - Type: PT_LOAD
+    Sections:
+      - Section: .text