[ELF] Add test for interaction of --gc-sections and undefined references

[jhenderson]

Summary

It is possible for a link to fail with an undefined reference, unless --gc-sections is specified, removing the reference in the process. This doesn't look to be tested anywhere explicitly, so I thought it useful to add a test for it to ensure the behaviour is maintained.

[ruiu]

LGTM

test/ELF/gc-sections-no-undef-error.s

7–8 ↗

(On Diff #130613)

You can write this in one line.

not ld.lld %t.o -o %t 2>&1 | FileCheck %s

[jhenderson]

test/ELF/gc-sections-no-undef-error.s

7–8 ↗

(On Diff #130613)

Thanks Rui. I thought I'd read somewhere on the mailing lists advising against doing that for some reason, but I can't find it now, so I may be misremembering it.

[ruiu]

I thought I'd read somewhere on the mailing lists advising against doing that for some reason, but I can't find it now, so I may be misremembering it.

Not sure if it is actually discouraged, but at least in lld it's conventional.

lld/trunk/test/ELF/gc-sections-no-undef-error.s

+# REQUIRES: x86
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
+
+# Sanity check that the link will fail with the undefined error without
+# gc-sections.
+# RUN: not ld.lld %t.o -o %t 2>&1 | FileCheck %s
+# CHECK: error: undefined symbol: undefined
+
+# RUN: ld.lld %t.o --gc-sections -o %t
+
+.section .text.unused,"ax",@progbits
+unused:
+  callq undefined
+
+.text
+.global _start
+_start:
+  nop