Index: llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
===================================================================
--- llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -620,7 +620,7 @@
 
     if (auto ParamValue = TII->describeLoadedValue(*I)) {
       if (ParamValue->first.isImm()) {
-        unsigned Val = ParamValue->first.getImm();
+        int64_t Val = ParamValue->first.getImm();
         DbgValueLoc DbgLocVal(ParamValue->second, Val);
         finishCallSiteParam(DbgLocVal, Reg);
       } else if (ParamValue->first.isReg()) {
Index: llvm/test/DebugInfo/X86/dbgcall-site-64-bit-imms.ll
===================================================================
--- /dev/null
+++ llvm/test/DebugInfo/X86/dbgcall-site-64-bit-imms.ll
@@ -0,0 +1,56 @@
+; RUN: llc -O1 -debug-entry-values -filetype=obj -o - %s | llvm-dwarfdump - | FileCheck %s
+
+; Verify that the 64-bit call site immediates are not truncated.
+;
+; Reproducer for PR43525.
+
+; Based on the following C program:
+;
+; #include <stdint.h>
+;
+; extern void foo(int64_t);
+;
+; int main() {
+;   foo(INT64_C(0x1122334455667788));
+;   foo(INT32_C(-100));
+; }
+
+; CHECK: DW_AT_GNU_call_site_value (DW_OP_constu 0x1122334455667788)
+; CHECK: DW_AT_GNU_call_site_value (DW_OP_constu 0xffffffffffffff9c)
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: nounwind uwtable
+define i32 @main() !dbg !12 {
+entry:
+  tail call void @foo(i64 1234605616436508552), !dbg !16
+  tail call void @foo(i64 -100), !dbg !17
+  ret i32 0, !dbg !18
+}
+
+declare !dbg !4 void @foo(i64)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!8, !9, !10}
+!llvm.ident = !{!11}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 10.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !3, nameTableKind: None)
+!1 = !DIFile(filename: "dbgcall-site-long-imms.c", directory: "/")
+!2 = !{}
+!3 = !{!4}
+!4 = !DISubprogram(name: "foo", scope: !1, file: !1, line: 3, type: !5, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !2)
+!5 = !DISubroutineType(types: !6)
+!6 = !{null, !7}
+!7 = !DIBasicType(name: "long int", size: 64, encoding: DW_ATE_signed)
+!8 = !{i32 2, !"Dwarf Version", i32 4}
+!9 = !{i32 2, !"Debug Info Version", i32 3}
+!10 = !{i32 1, !"wchar_size", i32 4}
+!11 = !{!"clang version 10.0.0"}
+!12 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 5, type: !13, scopeLine: 5, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+!13 = !DISubroutineType(types: !14)
+!14 = !{!15}
+!15 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!16 = !DILocation(line: 6, scope: !12)
+!17 = !DILocation(line: 7, scope: !12)
+!18 = !DILocation(line: 8, scope: !12)