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[clang][Sema] Accept gnu format attributes #160255

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Merged
higuoxing merged 10 commits into from
Sep 25, 2025
Merged

[clang][Sema] Accept gnu format attributes #160255

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a849465
[clang][Sema] Remove unused enum value: FormatStringType::Syslog.
higuoxing Sep 23, 2025
5273200
[clang][Sema] Accept gnu format attribtues.
higuoxing Sep 23, 2025
ab80b04
Merge branch 'main' into sema/gnu_format
higuoxing Sep 23, 2025
1850aa9
Update clang/test/Sema/attr-format.c
higuoxing Sep 23, 2025
31a4be7
Add gnu_strfmon.
higuoxing Sep 23, 2025
dc12a9a
Add release notes.
higuoxing Sep 23, 2025
e8893ed
Apply clang-format
higuoxing Sep 23, 2025
222e943
Merge branch 'main' into sema/gnu_format
higuoxing Sep 23, 2025
cd722a7
Update clang/docs/ReleaseNotes.rst
higuoxing Sep 25, 2025
84cecc7
Merge branch 'main' into sema/gnu_format
higuoxing Sep 25, 2025
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3 changes: 3 additions & 0 deletions clang/docs/ReleaseNotes.rst
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Expand Up @@ -272,6 +272,9 @@ Attribute Changes in Clang
attribute, allowing the attribute to only be attached to the declaration. Prior, this would be
treated as an error where the definition and declaration would have differing types.

- New format attributes ``gnu_printf``, ``gnu_scanf``, ``gnu_strftime`` and ``gnu_strfmon`` are added
as aliases for ``printf``, ``scanf``, ``strftime`` and ``strfmon``. (#GH16219)

Improvements to Clang's diagnostics
-----------------------------------
- Added a separate diagnostic group ``-Wfunction-effect-redeclarations``, for the more pedantic
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1 change: 0 additions & 1 deletion clang/include/clang/Sema/Sema.h
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Expand Up @@ -503,7 +503,6 @@ enum class FormatStringType {
FreeBSDKPrintf,
OSTrace,
OSLog,
Syslog,
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@shafik shafik Sep 25, 2025

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This change is not really explained. It feels like a drive by fix, which we usually discourage.

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@higuoxing higuoxing Sep 25, 2025

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Oh, I fixed it by a separate commit. When merging this PR, commits are squashed and I forget to write a commit message for this change. Shall I revert this part of change?

Unknown
};

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19 changes: 8 additions & 11 deletions clang/lib/Sema/SemaChecking.cpp
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Expand Up @@ -6866,11 +6866,12 @@ StringRef Sema::GetFormatStringTypeName(FormatStringType FST) {

FormatStringType Sema::GetFormatStringType(StringRef Flavor) {
return llvm::StringSwitch<FormatStringType>(Flavor)
.Case("scanf", FormatStringType::Scanf)
.Cases("printf", "printf0", "syslog", FormatStringType::Printf)
.Cases("gnu_scanf", "scanf", FormatStringType::Scanf)
.Cases("gnu_printf", "printf", "printf0", "syslog",
FormatStringType::Printf)
.Cases("NSString", "CFString", FormatStringType::NSString)
.Case("strftime", FormatStringType::Strftime)
.Case("strfmon", FormatStringType::Strfmon)
.Cases("gnu_strftime", "strftime", FormatStringType::Strftime)
.Cases("gnu_strfmon", "strfmon", FormatStringType::Strfmon)
.Cases("kprintf", "cmn_err", "vcmn_err", "zcmn_err",
FormatStringType::Kprintf)
.Case("freebsd_kprintf", FormatStringType::FreeBSDKPrintf)
Expand Down Expand Up @@ -6990,7 +6991,6 @@ bool Sema::CheckFormatArguments(ArrayRef<const Expr *> Args,
case FormatStringType::Kprintf:
case FormatStringType::FreeBSDKPrintf:
case FormatStringType::Printf:
case FormatStringType::Syslog:
Diag(FormatLoc, diag::note_format_security_fixit)
<< FixItHint::CreateInsertion(FormatLoc, "\"%s\", ");
break;
Expand Down Expand Up @@ -9120,8 +9120,7 @@ static void CheckFormatString(
if (Type == FormatStringType::Printf || Type == FormatStringType::NSString ||
Type == FormatStringType::Kprintf ||
Type == FormatStringType::FreeBSDKPrintf ||
Type == FormatStringType::OSLog || Type == FormatStringType::OSTrace ||
Type == FormatStringType::Syslog) {
Type == FormatStringType::OSLog || Type == FormatStringType::OSTrace) {
bool IsObjC =
Type == FormatStringType::NSString || Type == FormatStringType::OSTrace;
if (ReferenceFormatString == nullptr) {
Expand Down Expand Up @@ -9157,8 +9156,7 @@ bool Sema::CheckFormatStringsCompatible(
if (Type != FormatStringType::Printf && Type != FormatStringType::NSString &&
Type != FormatStringType::Kprintf &&
Type != FormatStringType::FreeBSDKPrintf &&
Type != FormatStringType::OSLog && Type != FormatStringType::OSTrace &&
Type != FormatStringType::Syslog)
Type != FormatStringType::OSLog && Type != FormatStringType::OSTrace)
return true;

bool IsObjC =
Expand Down Expand Up @@ -9192,8 +9190,7 @@ bool Sema::ValidateFormatString(FormatStringType Type,
if (Type != FormatStringType::Printf && Type != FormatStringType::NSString &&
Type != FormatStringType::Kprintf &&
Type != FormatStringType::FreeBSDKPrintf &&
Type != FormatStringType::OSLog && Type != FormatStringType::OSTrace &&
Type != FormatStringType::Syslog)
Type != FormatStringType::OSLog && Type != FormatStringType::OSTrace)
return true;

FormatStringLiteral RefLit = Str;
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5 changes: 3 additions & 2 deletions clang/lib/Sema/SemaDeclAttr.cpp
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Expand Up @@ -3629,10 +3629,11 @@ static FormatAttrKind getFormatAttrKind(StringRef Format) {
// Check for formats that get handled specially.
.Case("NSString", NSStringFormat)
.Case("CFString", CFStringFormat)
.Case("strftime", StrftimeFormat)
.Cases("gnu_strftime", "strftime", StrftimeFormat)

// Otherwise, check for supported formats.
.Cases("scanf", "printf", "printf0", "strfmon", SupportedFormat)
.Cases("gnu_scanf", "scanf", "gnu_printf", "printf", "printf0",
"gnu_strfmon", "strfmon", SupportedFormat)
.Cases("cmn_err", "vcmn_err", "zcmn_err", SupportedFormat)
.Cases("kprintf", "syslog", SupportedFormat) // OpenBSD.
.Case("freebsd_kprintf", SupportedFormat) // FreeBSD.
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8 changes: 8 additions & 0 deletions clang/test/Sema/attr-format.c
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Expand Up @@ -106,3 +106,11 @@ void b2(const char *a, ...) __attribute__((format(syslog, 1, 1))); // expecte
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}}

// gnu_printf
// same as format(printf(...))...
void a2(const char *a, ...) __attribute__((format(gnu_printf, 1, 2))); // no-error
void b2(const char *a, ...) __attribute__((format(gnu_printf, 1, 1))); // expected-error {{'format' attribute parameter 3 is out of bounds}}
void c2(const char *a, ...) __attribute__((format(gnu_printf, 0, 2))); // expected-error {{'format' attribute parameter 2 is out of bounds}}
void d2(const char *a, int c) __attribute__((format(gnu_printf, 1, 2))); // expected-warning {{GCC requires a function with the 'format' attribute to be variadic}}
void e2(char *str, int c, ...) __attribute__((format(gnu_printf, 2, 3))); // expected-error {{format argument not a string type}}
2 changes: 2 additions & 0 deletions clang/test/Sema/format-strings-scanf.c
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Expand Up @@ -30,6 +30,7 @@ int fscanf(FILE * restrict, const char * restrict, ...) ;
int scanf(const char * restrict, ...) ;
int sscanf(const char * restrict, const char * restrict, ...) ;
int my_scanf(const char * restrict, ...) __attribute__((__format__(__scanf__, 1, 2)));
int my_gnu_scanf(const char * restrict, ...) __attribute__((__format__(gnu_scanf, 1, 2)));

int vscanf(const char * restrict, va_list);
int vfscanf(FILE * restrict, const char * restrict, va_list);
Expand Down Expand Up @@ -98,6 +99,7 @@ void test_variants(int *i, const char *s, ...) {
fscanf(f, "%ld", i); // expected-warning{{format specifies type 'long *' but the argument has type 'int *'}}
sscanf(buf, "%ld", i); // expected-warning{{format specifies type 'long *' but the argument has type 'int *'}}
my_scanf("%ld", i); // expected-warning{{format specifies type 'long *' but the argument has type 'int *'}}
my_gnu_scanf("%ld", i); // expected-warning{{format specifies type 'long *' but the argument has type 'int *'}}

va_list ap;
va_start(ap, s);
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6 changes: 6 additions & 0 deletions clang/test/Sema/format-strings.c
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Expand Up @@ -678,15 +678,21 @@ void pr18905(void) {
}

void __attribute__((format(strfmon,1,2))) monformat(const char *fmt, ...);
void __attribute__((format(gnu_strfmon,1,2))) gnu_monformat(const char *fmt, ...);
void __attribute__((format(strftime,1,0))) dateformat(const char *fmt);
void __attribute__((format(gnu_strftime,1,0))) gnu_dateformat(const char *fmt);

// Other formats
void test_other_formats(void) {
char *str = "";
monformat("", 1); // expected-warning{{format string is empty}}
monformat(str); // expected-warning{{format string is not a string literal (potentially insecure)}}
gnu_monformat("", 1); // expected-warning{{format string is empty}}
gnu_monformat(str); // expected-warning{{format string is not a string literal (potentially insecure)}}
dateformat(""); // expected-warning{{format string is empty}}
dateformat(str); // no-warning (using strftime non-literal is not unsafe)
gnu_dateformat(""); // expected-warning{{format string is empty}}
gnu_dateformat(str); // no-warning (using strftime non-literal is not unsafe)
}

// Do not warn about unused arguments coming from system headers.
Expand Down