[llvm] [Bolt] fix a wrong relocation update issue with weak references (PR #69136)

[Maksim Panchenko via llvm-commits]

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@@ -0,0 +1,34 @@
+// This test checks whether BOLT can correctly handle relocations against weak symbols.
+
+// RUN: %clang %cflags -Wl,-z,notext -shared -Wl,-q %s -o %t.so
+// RUN: llvm-bolt %t.so -o %t.so.bolt
+// RUN: llvm-nm -n %t.so.bolt > %t.out.txt
+// RUN: llvm-objdump -dj .rodata %t.so.bolt >> %t.out.txt
+// RUN: FileCheck %s --input-file=%t.out.txt
+
+# CHECK: w func_1
+# CHECK: {{0+}}[[#%x,ADDR:]] W func_2
+
+# CHECK: {{.*}} <.rodata>:
+# CHECK-NEXT: {{.*}} .word 0x00000000
+# CHECK-NEXT: {{.*}} .word 0x00000000
+# CHECK-NEXT: {{.*}} .word 0x{{[0]+}}[[#ADDR]]
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maksfb wrote:

> It's true that before it is 0 here. But it is up to the linker to set value here or not. and for example to support RELR we need to set values here. I don't think it is a problem and would rather set the value, than not.

Can we rely on the linker's decision in such cases? I.e., if the linker decided to put 0, keep it at that. If it was the symbol value, then we can update it.

https://github.com/llvm/llvm-project/pull/69136