[ARM]Add a NOP instruction to make LLVM generate a mapping symbol

[shankare]

Summary

This is a test change applicable for ARM targets.

Previously LLVM would generate a mapping symbol when code contains only
data. This was changed as part of

https://reviews.llvm.org/D30724

and to be more close to the ARM ELF ABI.

The test case is changed to check for behavior with minimal changes.

[ruiu]

Peter Smith, are you fine with this change?

[jmolloy]

Hi,

I'm confused about how this test change is actually checking for any change in behaviour. No CHECK lines have been updated - have I missed something? Is the test currently failing?

Cheers,

James

[peter.smith]

My understanding is that this test failed when a change went in to llvm-mc to not emit the mapping symbol $d.0 when the section contains only data. The test here is checking for the $d.0. Adding the nop forces the creation of a $a.0 which then forces the creation of the $d.0, this will make the test more robust against llvm-mc changes.

I think that this is a reasonably pragmatic change, I'm happy to see it go in although I think it would be worth a comment saying something like Force creation of $d.0 mapping symbol. Another possibility is to just remove the RELATIVE: $d.0: line as it isn't necessary for the output of the test (check R_ARM_TARGET1).

[shankare]

Can you please merge the change ?

[peter.smith]

I can do, although there isn't any special permissions to commit to lld, if you can commit to llvm then you can commit to lld. Let me know if you'd prefer to do it yourself? Otherwise I'll do it in an hour.

[peter.smith]

Ok now merged as r299212

lld/trunk/test/ELF/arm-target1.s

 // RELOC:   .rel.text {
 // RELOC:     0x0 R_ARM_TARGET1 patatino 0x0
 // RELOC:   }
 // RELOC: ]
 
 .text
   .word patatino(target1)
   patatino:
-
+        .word 32
+// Force generation of $d.0 as section is not all data
+  nop
 // RELATIVE: Disassembly of section .text:
 // RELATIVE: $d.0:
 // RELATIVE:     1000:       04 00 00 00     .word   0x00000004
 // RELATIVE: SYMBOL TABLE:
 // RELATIVE: 00001004         .text           00000000 patatino
 
 // ABS: {{.*}}.o:(.text+0x0): can't create dynamic relocation R_ARM_TARGET1 against symbol 'patatino' defined in {{.*}}.o