[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

14

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

14

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 ↗

(On Diff #159002)

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 ↗

(On Diff #159002)

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.s

+// REQUIRES: arm
+// RUN: ld.lld %S/Inputs/arm-thumb-narrow-undefined-weak.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
+
+// llvm-mc relaxes the b.n to a b.w as undefined_weak is external to the
+// section so we must use a binary object produced by GNU as using the 
+// following assembly
+
+//        .thumb
+//        .syntax unified
+//
+//        .weak undefined_weak
+//        .globl _start
+//        .type _start, %function
+// __start: b.n undefine_weak