Missing support for labels in .org statements

[nlewycky]

Bugzilla Link	9245
Resolution	FIXED
Resolved on	Feb 20, 2011 18:33
Version	unspecified
OS	Linux
Blocks	#4440
Attachments	testcase
CC	@kjwinchester

Extended Description

The linux kernel (2.6.38-rc5) doesn't build because of a problem in llvm-mc and the BUG() macro which is used throughout.

Please see the C testcase attached. It triggers easily:

$ clang y.c -c -o y.o
fatal error: error in backend: expected assembly-time absolute expression

while having clang emit a .s file and then using GAS to assemble it works fine. However:

$ clang y.c -S -o y.s
$ llvm-mc -assemble y.s -filetype=obj
LLVM ERROR: expected assembly-time absolute expression

[llvmbot]

Reduced testcase:

foo:
.org foo+16

[llvmbot]

proposed patch
I am not sure what the best way to implement this is.

The more direct one would be to add a really_force_to_be_constant argument to EvaluateAsRelocatableImpl. Given how complicated that function already is and how limited our implementation of org is, what the attached patch does is hack .org a bit more.

Currently we support only constants. This patch adds support for simple expressions by converting

.org foo + 10

to

bar:
.fill (foo-bar) + 10

If it is sufficient for the cases you have, it should be easy to clean it up (add support in the asm streamer for example).

[llvmbot]

Fixed in 126091. Please open another bug if you find fancier .org directives in use.

[lattner]

Awesome, thanks Rafael!