[LLD][ELF][ARM] Test undefined weak symbol for Thumb narrow branch

[peter.smith]

Summary

Add a test for the R_ARM_THM_JUMP11 relocation to an undefined symbol. We have to use a binary object assembled with the GNU assembler as llvm-mc relaxes the narrow branch to a b.w which uses the R_ARM_THM_JUMP24 relocation.

This adds code coverage for a line introduced in D26240

[grimar]

LGTM. Thanks for this patch, Peter!

[grimar]

I would add information about how the object was produced though. (version of GNU as + code used?)

[peter.smith]

I've updated the comment to mention the gcc version. The code for the object is in the comment, I've made that a bit clearer.

Will wait till Monday to give Rui a chance to take a look.

[grimar]

test/ELF/arm-thumb-undefined-weak-narrow.s

13 ↗

(On Diff #158974)

btw, it is saying that you used "arm-linux-gnueabihf-gcc (Linaro GCC 5.3-2016.02) "

I wonder, can you use yaml2obj?

[grimar]

test/ELF/arm-thumb-undefined-weak-narrow.s

13 ↗

(On Diff #158974)

I think using GCC is fine though. What I meant is that my concern is about using
the custom compiler ("Linaro GCC" in this case). I hope regular GCC has the same output.

[peter.smith]

Thanks for the suggestion to use yaml2obj. I keep forgetting about that. I've been able to make the same test case.

[grimar]

LGTM, thanks!

test/ELF/arm-thumb-undefined-weak-narrow.test

34

I think it should be possible to place R_ARM_THM_JUMP11 here instead of 102.

[grimar]

test/ELF/arm-thumb-undefined-weak-narrow.test

3

You do not need it, btw, I think.

[peter.smith]

Thanks for the comments. I've updated the diff.

[ruiu]

LGTM

test/ELF/arm-thumb-undefined-weak-narrow.test

+# REQUIRES: arm
+# RUN: yaml2obj %s -o %t.o        
+# RUN: llvm-objdump -triple=thumbv7a-linux-gnueabi -d -r %t.o 
+# RUN: ld.lld %t.o -o %t
+# RUN: llvm-objdump -triple=thumbv7a-linux-gnueabi -d %t | FileCheck %s
+
+# CHECK: Disassembly of section .text:
+# CHECK-NEXT:_start:
+# CHECK-NEXT:    11000:       ff e7   b       #-2
+
+# Test the R_ARM_THM_JUMP11 relocation (102) to an undefined weak reference
+# It should resolve to the next instruction, which is an offset of -2 which
+# when added to the Thumb PC-bias of 4 is +2. We can't use llvm-mc to construct
+# the object as it relaxes b.n to b.w (R_ARM_JUMP24).
+
+!ELF
+FileHeader:
+  Class:           ELFCLASS32
+  Data:            ELFDATA2LSB
+  Type:            ET_REL
+  Machine:         EM_ARM
+Sections:
+  - Type:            SHT_PROGBITS
+    Name:            .text
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    Content:         "fee7"
+  - Type:            SHT_REL
+    Name:            .rel.text
+    Link:            .symtab
+    Info:            .text
+    Relocations:
+      - Offset:          0
+        Symbol:          undefined_weak
+        Type:            102
+
+Symbols:
+ Global:
+   - Type:             STT_FUNC
+     Name:             _start
+     Value:            1
+     Section:          .text
+ Local:
+   - Type:             STT_NOTYPE
+     Name:             "$t"
+     Section:          .text
+     Value:            0
+ Weak:
+   - Type:             STT_NOTYPE
+     Name:             undefined_weak
+     Value:            0
+