diff --git a/llvm/include/llvm/ProfileData/SampleProf.h b/llvm/include/llvm/ProfileData/SampleProf.h
--- a/llvm/include/llvm/ProfileData/SampleProf.h
+++ b/llvm/include/llvm/ProfileData/SampleProf.h
@@ -149,8 +149,9 @@
     return "CSNameTableSection";
   case SecLBRProfile:
     return "LBRProfileSection";
+  default:
+    return "UnknownSection";
   }
-  llvm_unreachable("A SecType has no name for output");
 }
 
 // Entry type of section header table used by SampleProfileExtBinaryBaseReader
diff --git a/llvm/include/llvm/ProfileData/SampleProfReader.h b/llvm/include/llvm/ProfileData/SampleProfReader.h
--- a/llvm/include/llvm/ProfileData/SampleProfReader.h
+++ b/llvm/include/llvm/ProfileData/SampleProfReader.h
@@ -786,6 +786,8 @@
   virtual std::error_code verifySPMagic(uint64_t Magic) override;
   virtual std::error_code
   readCustomSection(const SecHdrTableEntry &Entry) override {
+    // Update the data reader pointer to the end of the section.
+    Data += Entry.Size;
     return sampleprof_error::success;
   };
 
diff --git a/llvm/test/tools/llvm-profdata/Inputs/unknown.section.extbin.profdata b/llvm/test/tools/llvm-profdata/Inputs/unknown.section.extbin.profdata
new file mode 100644
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000
GIT binary patch
literal 0
Hc$@<O00001

literal 0
Hc$@<O00001

diff --git a/llvm/test/tools/llvm-profdata/forward-compatible.test b/llvm/test/tools/llvm-profdata/forward-compatible.test
new file mode 100644
--- /dev/null
+++ b/llvm/test/tools/llvm-profdata/forward-compatible.test
@@ -0,0 +1,26 @@
+RUN: llvm-profdata show -sample %S/Inputs/unknown.section.extbin.profdata | FileCheck %s
+RUN: llvm-profdata show -sample -show-sec-info-only %S/Inputs/unknown.section.extbin.profdata | FileCheck %s -check-prefix=HDR
+
+# The input unknown.section.extbin.profdata contains an unknown section type
+# which uses an enum value which won't be used in the near future. Check
+# llvm-profdata can read it without problem. This is to ensure adding new
+# section in extbinary format for SampleFDO won't cause forward compatibility
+# issue.
+
+CHECK: Function: main: 366846, 0, 3 sampled lines
+CHECK-NEXT: Samples collected in the function's body {
+CHECK-NEXT:   2.1: 60401
+CHECK-NEXT:   3: 0
+CHECK-NEXT:   4: 0
+CHECK-NEXT: }
+
+HDR: ProfileSummarySection - Offset: 242, Size: 121, Flags: {}
+HDR-NEXT: NameTableSection - Offset: 363, Size: 6, Flags: {}
+HDR-NEXT: UnknownSection - Offset: 369, Size: 1, Flags: {}
+HDR-NEXT: FuncOffsetTableSection - Offset: 391, Size: 3, Flags: {}
+HDR-NEXT: LBRProfileSection - Offset: 370, Size: 21, Flags: {}
+HDR-NEXT: ProfileSymbolListSection - Offset: 391, Size: 0, Flags: {}
+HDR-NEXT: FunctionMetadata - Offset: 394, Size: 0, Flags: {}
+HDR-NEXT: Header Size: 242
+HDR-NEXT: Total Sections Size: 152
+HDR-NEXT: File Size: 394