[llvm-dev] Create the GlobalVariable which have extern in one header file

Mustakimur Khandaker via llvm-dev llvm-dev at lists.llvm.org
Fri Feb 22 06:15:22 PST 2019

I have changed it to ExternalLinkage. Now, in LLVM IR, it looks like that:

@DATA_TABLE = external global [0 x i8*], section "data_section", align 16 #0
@DATA_TABLE.1 = global [10 x i8*] [i8* inttoptr (i64 53415718 to i8*), i8* bitcast (void (%class.Hello*)* @_ZN5Hello5ptofnEv to i8*),...], section "data_section", align 16 #0

In my uses:
%arrayidx = getelementptr inbounds [0 x i8*], [0 x i8*]* @DATA_TABLE, i64 0, i64 %3

Why it is creating another global variable instead of linking? Is that because of array size mismatch?

Here is my code:

GlobalVariable *old = M.getGlobalVariable("DATA_TABLE");

GlobalVariable *gNew = new GlobalVariable(
M, blockItems->getType(), false, GlobalValue::ExternalLinkage,
blockItems, "DATA_TABLE");

On Feb 22 2019, at 12:02 am, Tim Northover <t.p.northover at gmail.com> wrote:
On Thu, 21 Feb 2019 at 18:42, Mustakimur Khandaker via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
GlobalVariable *gvar_data = new GlobalVariable(
M, blockItems->getType(), true, GlobalValue::CommonLinkage,
blockItems, "DATA_TABLE");

I am not sure if I am using the correct Linkage or not.
The pass has failed to complete it. Here is the runtime fault. Any guess what I am doing incorrect?

As you've guessed, it's the linkage.

"common" is the name for the C situation where multiple source files
simply declare "int a;" with nothing else specified. The names get
merged, and the variable gets zero-initialized by default. A "real"
definition (like you're trying to provide) would take precedence over
this and specify the actual data.

You almost certainly want GlobalValue::ExternalLinkage for a
bog-standard global variable.


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