[llvm-dev] why do undefined globals end up in .data instead of .bss?

Andrew Kelley via llvm-dev llvm-dev at lists.llvm.org
Mon Apr 24 11:55:05 PDT 2017

On Mon, Apr 24, 2017 at 2:53 PM, Friedman, Eli <efriedma at codeaurora.org>

> On 4/23/2017 10:10 AM, Andrew Kelley via llvm-dev wrote:
>> Here is a module:
>> @vals = internal unnamed_addr global [20000000 x i32] undef, align 4
>> LLVM puts the global in the .data section, and results in a 77MB .o file
>> of mostly zeroes. Why does this variable not go in the .bss section?
> I think it's just an oversight; it doesn't matter for clang because it
> never emits globals like that.  See TargetLoweringObjectFile::getKindForGlobal
> for the relevant logic.

I see, thanks. Would a patch be welcome which changed this behavior? Or I
suppose I could emit zeroinitializer instead of undef. But it seems like
undef is the more correct value.
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