[CodeGen][KCFI] Emit signed comment for .set directive value

When emitting the assembly .set directive, KCFI needs to use
getZExtValue(). However, this means that FileCheck pattern matching can't
match between the .set directive and the IR when the high bit of a 32-bit
value is set. We had gotten lucky with the existing tests happening to
just not have had the high bit set. The coming hash change will expose
this, though.

LLVM IR's default printing behavior uses APInt::operator<<, which calls
APInt::print(OS, /*isSigned=*/true). This means KCFI operand bundles in
call instructions print as signed (e.g. [ "kcfi"(i32 -1208803271) ]),
and KCFI type metadata prints as signed (e.g. !3 = !{i32 -1208803271}).
Changing the IR to print unsigned i32 values would impact hundreds of
existing tests, so it is best to just leave it be.

Update the KCFI .set direct to use getSExtValue() in a comment so that
we can both build correctly and use FileCheck with pattern matching in
tests.

Signed-off-by: Kees Cook <[email protected]>

Author: kees

clang/lib/CodeGen/CodeGenModule.cpp

@@ -3189,7 +3189,8 @@ void CodeGenModule::finalizeKCFITypes() {
       continue;
 
     std::string Asm = (".weak __kcfi_typeid_" + Name + "\n.set __kcfi_typeid_" +
-                       Name + ", " + Twine(Type->getZExtValue()) + "\n")
+                       Name + ", " + Twine(Type->getZExtValue()) + " # " +
+                       Twine(Type->getSExtValue()) + "\n")
                           .str();
     M.appendModuleInlineAsm(Asm);
   }

clang/test/CodeGen/cfi-salt.c

@@ -27,9 +27,9 @@ typedef unsigned int (* __cfi_salt ufn_salt_t)(void);
 
 /// Must emit __kcfi_typeid symbols for address-taken function declarations
 // CHECK: module asm ".weak __kcfi_typeid_[[F4:[a-zA-Z0-9_]+]]"
-// CHECK: module asm ".set __kcfi_typeid_[[F4]], [[#%d,LOW_SODIUM_HASH:]]"
+// CHECK: module asm ".set __kcfi_typeid_[[F4]], {{[0-9]+}} # [[#%d,LOW_SODIUM_HASH:]]"
 // CHECK: module asm ".weak __kcfi_typeid_[[F4_SALT:[a-zA-Z0-9_]+]]"
-// CHECK: module asm ".set __kcfi_typeid_[[F4_SALT]], [[#%d,ASM_SALTY_HASH:]]"
+// CHECK: module asm ".set __kcfi_typeid_[[F4_SALT]], {{[0-9]+}} # [[#%d,ASM_SALTY_HASH:]]"
 
 /// Must not __kcfi_typeid symbols for non-address-taken declarations
 // CHECK-NOT: module asm ".weak __kcfi_typeid_f6"

clang/test/CodeGen/kcfi.c

@@ -7,7 +7,7 @@
 
 /// Must emit __kcfi_typeid symbols for address-taken function declarations
 // CHECK: module asm ".weak __kcfi_typeid_[[F4:[a-zA-Z0-9_]+]]"
-// CHECK: module asm ".set __kcfi_typeid_[[F4]], [[#%d,HASH:]]"
+// CHECK: module asm ".set __kcfi_typeid_[[F4]], {{[0-9]+}} # [[#%d,HASH:]]"
 /// Must not __kcfi_typeid symbols for non-address-taken declarations
 // CHECK-NOT: module asm ".weak __kcfi_typeid_{{f6|_Z2f6v}}"