release/19.x: [clang][Sema] Add support for OpenBSD's syslog format attribute (#97366)

[llvmbot]

Backport e788788

Requested by: @brad0

[llvmbot]

@Sirraide What do you think about merging this PR to the release branch?

[llvmbot]

@llvm/pr-subscribers-clang

Author: None (llvmbot)

Changes

Backport e788788

Requested by: @brad0

---

Full diff: https://github.com/llvm/llvm-project/pull/100703.diff

5 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+2)
• (modified) clang/include/clang/Sema/Sema.h (+1)
• (modified) clang/lib/Sema/SemaChecking.cpp (+3-2)
• (modified) clang/lib/Sema/SemaDeclAttr.cpp (+2-2)
• (modified) clang/test/Sema/attr-format.c (+7)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 5b6ee9830b507..562f383e3b232 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -629,6 +629,8 @@ Attribute Changes in Clang
   The attributes declare constraints about a function's behavior pertaining to blocking and
   heap memory allocation.
 
+- Introduced a new format attribute ``__attribute__((format(syslog, 1, 2)))`` from OpenBSD.
+
 Improvements to Clang's diagnostics
 -----------------------------------
 - Clang now emits an error instead of a warning for ``-Wundefined-internal``
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index 7bfdaaae45a93..2ec6367eccea0 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -2214,6 +2214,7 @@ class Sema final : public SemaBase {
     FST_FreeBSDKPrintf,
     FST_OSTrace,
     FST_OSLog,
+    FST_Syslog,
     FST_Unknown
   };
   static FormatStringType GetFormatStringType(const FormatAttr *Format);
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index cf1196ad23c21..5dfeae27a3aca 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -6030,7 +6030,7 @@ static const Expr *maybeConstEvalStringLiteral(ASTContext &Context,
 Sema::FormatStringType Sema::GetFormatStringType(const FormatAttr *Format) {
   return llvm::StringSwitch<FormatStringType>(Format->getType()->getName())
       .Case("scanf", FST_Scanf)
-      .Cases("printf", "printf0", FST_Printf)
+      .Cases("printf", "printf0", "syslog", FST_Printf)
       .Cases("NSString", "CFString", FST_NSString)
       .Case("strftime", FST_Strftime)
       .Case("strfmon", FST_Strfmon)
@@ -6124,6 +6124,7 @@ bool Sema::CheckFormatArguments(ArrayRef<const Expr *> Args,
     case FST_Kprintf:
     case FST_FreeBSDKPrintf:
     case FST_Printf:
+    case FST_Syslog:
       Diag(FormatLoc, diag::note_format_security_fixit)
         << FixItHint::CreateInsertion(FormatLoc, "\"%s\", ");
       break;
@@ -7860,7 +7861,7 @@ static void CheckFormatString(
 
   if (Type == Sema::FST_Printf || Type == Sema::FST_NSString ||
       Type == Sema::FST_FreeBSDKPrintf || Type == Sema::FST_OSLog ||
-      Type == Sema::FST_OSTrace) {
+      Type == Sema::FST_OSTrace || Type == Sema::FST_Syslog) {
     CheckPrintfHandler H(
         S, FExpr, OrigFormatExpr, Type, firstDataArg, numDataArgs,
         (Type == Sema::FST_NSString || Type == Sema::FST_OSTrace), Str, APK,
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index 5fd8622c90dd8..3e53182b5130c 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -3397,8 +3397,8 @@ static FormatAttrKind getFormatAttrKind(StringRef Format) {
       // Otherwise, check for supported formats.
       .Cases("scanf", "printf", "printf0", "strfmon", SupportedFormat)
       .Cases("cmn_err", "vcmn_err", "zcmn_err", SupportedFormat)
-      .Case("kprintf", SupportedFormat)         // OpenBSD.
-      .Case("freebsd_kprintf", SupportedFormat) // FreeBSD.
+      .Cases("kprintf", "syslog", SupportedFormat) // OpenBSD.
+      .Case("freebsd_kprintf", SupportedFormat)    // FreeBSD.
       .Case("os_trace", SupportedFormat)
       .Case("os_log", SupportedFormat)
 
diff --git a/clang/test/Sema/attr-format.c b/clang/test/Sema/attr-format.c
index 1f4c864d4f78b..5a8b1ac9eca5c 100644
--- a/clang/test/Sema/attr-format.c
+++ b/clang/test/Sema/attr-format.c
@@ -99,3 +99,10 @@ void forward_fixed(const char *fmt, _Bool b, char i, short j, int k, float l, do
   a(fmt, b, i, j, k, l, m);
 }
 
+// OpenBSD
+// same as format(printf(...))...
+void a2(const char *a, ...) __attribute__((format(syslog, 1, 2)));    // no-error
+void b2(const char *a, ...) __attribute__((format(syslog, 1, 1)));    // expected-error {{'format' attribute parameter 3 is out of bounds}}
+void c2(const char *a, ...) __attribute__((format(syslog, 0, 2)));    // expected-error {{'format' attribute parameter 2 is out of bounds}}
+void d2(const char *a, int c) __attribute__((format(syslog, 1, 2)));  // expected-warning {{GCC requires a function with the 'format' attribute to be variadic}}
+void e2(char *str, int c, ...) __attribute__((format(syslog, 2, 3))); // expected-error {{format argument not a string type}}

[Endilll]

I'm not sure we want to backport a feature this late.
I also don't see any discussion of this being critical for 19 in #97366

[Sirraide]

Yeah, this isn’t really a bugfix, it’s adding a small feature that doesn’t seem critical or anything like that to me either, so I don’t think there is a need to backport this.

[tru]

We are open to finish of features in RC1-2, but if there is no big need for this it's better to leave it out.

[AaronBallman]

I don't see a need to backport this for 19.x, it seems reasonable to let it bake for a while in 20.x (though I would be surprised if there was significant negative fallout from the changes).

[tru]

I will close this since there seems to be consensus that we don't need to backport it. If there is differing opinions - feel free to re-open.