[libc-commits] [libc] [libc] Reimplement IN6_IS_ADDR_* macros using statement expressions (PR #209772)
Pavel Labath via libc-commits
libc-commits at lists.llvm.org
Wed Jul 15 07:48:23 PDT 2026
https://github.com/labath updated https://github.com/llvm/llvm-project/pull/209772
>From 68497491f58a6db4fe998ab989dbcb6665645ae4 Mon Sep 17 00:00:00 2001
From: Pavel Labath <pavel at labath.sk>
Date: Wed, 15 Jul 2026 14:16:03 +0000
Subject: [PATCH 1/2] [libc] Reimplement IN6_IS_ADDR_* macros using statement
expressions
This patch fixes three issues with the previous implementation:
- the macro argument was being evaluated more than once
- casting to other types (uint32_t in particular) was an aliasing violation
- it was casting to non-const pointers, resulting in compiler errors in cases
where the user passes a const ptr.
A statement expression fixes the first issue by using a temporary variable. The
second issue is fixed by using the appropriate members of struct in6_addr. The
last issue is fixed by dropping the cast completely. This requires the user to
pass a correctly types pointer (as POSIX requires). Implementations keep it for
compatibility with old code passing void * and similar, but a quick survey shows
that most modern code passes the correct types. If this turns out to be an
issue, we can easily add the cast (to a const type) back.
Implementation notes:
- IN6_IS_ADDR_MULTICAST doesn't use the statement expression because the
argument is evaluated only once
- I use private helper macros (__IN6_IS_ADDR_UNSPECIFIED and
__IN6_IS_ADDR_LOOPBACK) so IN6_IS_ADDR_V4COMPAT does not nest statement
expressions
- I considered using private entrypoints (like we do with cpuset macros) instead
of statement expressions, but decided against it because these macros are
simpler and would thus result in a much higher boilerplate-to-useful-code
ratio (particularly given our restriction on calling other entrypoints)
Assisted by Gemini.
---
.../llvm-libc-macros/netinet-in-macros.h | 96 ++++++++++-------
libc/test/include/netinet_in_test.cpp | 102 +++++++++---------
2 files changed, 111 insertions(+), 87 deletions(-)
diff --git a/libc/include/llvm-libc-macros/netinet-in-macros.h b/libc/include/llvm-libc-macros/netinet-in-macros.h
index 9664d512615b9..d7c9d2d2a7e9c 100644
--- a/libc/include/llvm-libc-macros/netinet-in-macros.h
+++ b/libc/include/llvm-libc-macros/netinet-in-macros.h
@@ -11,6 +11,7 @@
#include "../__llvm-libc-common.h"
#include "../llvm-libc-types/in_addr_t.h"
+#include "../llvm-libc-types/struct_in6_addr.h"
#define IPPROTO_IP 0
#define IPPROTO_ICMP 1
@@ -42,64 +43,85 @@
// int and takes a single argument of type const struct in6_addr *:
// https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/netinet_in.h.html
+#define __IN6_IS_ADDR_UNSPECIFIED(a) \
+ ((a)->s6_addr32[0] == 0 && (a)->s6_addr32[1] == 0 && \
+ (a)->s6_addr32[2] == 0 && (a)->s6_addr32[3] == 0)
+
+#define __IN6_IS_ADDR_LOOPBACK(a) \
+ ((a)->s6_addr32[0] == 0 && (a)->s6_addr32[1] == 0 && \
+ (a)->s6_addr32[2] == 0 && (a)->s6_addr[12] == 0 && \
+ (a)->s6_addr[13] == 0 && (a)->s6_addr[14] == 0 && (a)->s6_addr[15] == 1)
+
#define IN6_IS_ADDR_UNSPECIFIED(a) \
- ((__LLVM_LIBC_CAST(reinterpret_cast, uint32_t *, a)[0]) == 0 && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint32_t *, a)[1]) == 0 && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint32_t *, a)[2]) == 0 && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint32_t *, a)[3]) == 0)
+ (__extension__({ \
+ const struct in6_addr *__a = (a); \
+ __IN6_IS_ADDR_UNSPECIFIED(__a); \
+ }))
#define IN6_IS_ADDR_LOOPBACK(a) \
- ((__LLVM_LIBC_CAST(reinterpret_cast, uint32_t *, a)[0]) == 0 && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint32_t *, a)[1]) == 0 && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint32_t *, a)[2]) == 0 && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[12]) == 0 && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[13]) == 0 && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[14]) == 0 && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[15]) == 1)
+ (__extension__({ \
+ const struct in6_addr *__a = (a); \
+ __IN6_IS_ADDR_LOOPBACK(__a); \
+ }))
-#define IN6_IS_ADDR_MULTICAST(a) \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[0]) == 0xff
+#define IN6_IS_ADDR_MULTICAST(a) ((a)->s6_addr[0] == 0xff)
#define IN6_IS_ADDR_LINKLOCAL(a) \
- ((__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[0]) == 0xfe && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[1] & 0xc0) == 0x80)
+ (__extension__({ \
+ const struct in6_addr *__a = (a); \
+ __a->s6_addr[0] == 0xfe && (__a->s6_addr[1] & 0xc0) == 0x80; \
+ }))
#define IN6_IS_ADDR_SITELOCAL(a) \
- ((__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[0]) == 0xfe && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[1] & 0xc0) == 0xc0)
+ (__extension__({ \
+ const struct in6_addr *__a = (a); \
+ __a->s6_addr[0] == 0xfe && (__a->s6_addr[1] & 0xc0) == 0xc0; \
+ }))
#define IN6_IS_ADDR_V4MAPPED(a) \
- ((__LLVM_LIBC_CAST(reinterpret_cast, uint32_t *, a)[0]) == 0 && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint32_t *, a)[1]) == 0 && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[8]) == 0 && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[9]) == 0 && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[10]) == 0xff && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[11]) == 0xff)
+ (__extension__({ \
+ const struct in6_addr *__a = (a); \
+ __a->s6_addr32[0] == 0 && __a->s6_addr32[1] == 0 && \
+ __a->s6_addr[8] == 0 && __a->s6_addr[9] == 0 && \
+ __a->s6_addr[10] == 0xff && __a->s6_addr[11] == 0xff; \
+ }))
#define IN6_IS_ADDR_V4COMPAT(a) \
- ((__LLVM_LIBC_CAST(reinterpret_cast, uint32_t *, a)[0]) == 0 && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint32_t *, a)[1]) == 0 && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint32_t *, a)[2]) == 0 && \
- !IN6_IS_ADDR_UNSPECIFIED(a) && !IN6_IS_ADDR_LOOPBACK(a))
+ (__extension__({ \
+ const struct in6_addr *__a = (a); \
+ __a->s6_addr32[0] == 0 && __a->s6_addr32[1] == 0 && \
+ __a->s6_addr32[2] == 0 && !__IN6_IS_ADDR_UNSPECIFIED(__a) && \
+ !__IN6_IS_ADDR_LOOPBACK(__a); \
+ }))
#define IN6_IS_ADDR_MC_NODELOCAL(a) \
- (IN6_IS_ADDR_MULTICAST(a) && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[1] & 0xf) == 0x1)
+ (__extension__({ \
+ const struct in6_addr *__a = (a); \
+ IN6_IS_ADDR_MULTICAST(__a) && (__a->s6_addr[1] & 0xf) == 0x1; \
+ }))
#define IN6_IS_ADDR_MC_LINKLOCAL(a) \
- (IN6_IS_ADDR_MULTICAST(a) && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[1] & 0xf) == 0x2)
+ (__extension__({ \
+ const struct in6_addr *__a = (a); \
+ IN6_IS_ADDR_MULTICAST(__a) && (__a->s6_addr[1] & 0xf) == 0x2; \
+ }))
#define IN6_IS_ADDR_MC_SITELOCAL(a) \
- (IN6_IS_ADDR_MULTICAST(a) && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[1] & 0xf) == 0x5)
+ (__extension__({ \
+ const struct in6_addr *__a = (a); \
+ IN6_IS_ADDR_MULTICAST(__a) && (__a->s6_addr[1] & 0xf) == 0x5; \
+ }))
#define IN6_IS_ADDR_MC_ORGLOCAL(a) \
- (IN6_IS_ADDR_MULTICAST(a) && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[1] & 0xf) == 0x8)
+ (__extension__({ \
+ const struct in6_addr *__a = (a); \
+ IN6_IS_ADDR_MULTICAST(__a) && (__a->s6_addr[1] & 0xf) == 0x8; \
+ }))
#define IN6_IS_ADDR_MC_GLOBAL(a) \
- (IN6_IS_ADDR_MULTICAST(a) && \
- (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[1] & 0xf) == 0xe)
+ (__extension__({ \
+ const struct in6_addr *__a = (a); \
+ IN6_IS_ADDR_MULTICAST(__a) && (__a->s6_addr[1] & 0xf) == 0xe; \
+ }))
#endif // LLVM_LIBC_MACROS_NETINET_IN_MACROS_H
diff --git a/libc/test/include/netinet_in_test.cpp b/libc/test/include/netinet_in_test.cpp
index 2fb46a9227c07..03f4c052ab9b2 100644
--- a/libc/test/include/netinet_in_test.cpp
+++ b/libc/test/include/netinet_in_test.cpp
@@ -10,68 +10,70 @@
#include "test/UnitTest/Test.h"
TEST(LlvmLibcNetinetInTest, IN6Macro) {
- char buff[16] = {};
+ struct in6_addr addr = {};
+ const struct in6_addr *const_addr = &addr;
- EXPECT_TRUE(IN6_IS_ADDR_UNSPECIFIED(buff));
+ EXPECT_TRUE(IN6_IS_ADDR_UNSPECIFIED(&addr));
+ EXPECT_TRUE(IN6_IS_ADDR_UNSPECIFIED(const_addr));
for (int i = 0; i < 16; ++i) {
- buff[i] = 1;
- EXPECT_FALSE(IN6_IS_ADDR_UNSPECIFIED(buff));
- buff[i] = 0;
+ addr.s6_addr[i] = 1;
+ EXPECT_FALSE(IN6_IS_ADDR_UNSPECIFIED(&addr));
+ addr.s6_addr[i] = 0;
}
- EXPECT_FALSE(IN6_IS_ADDR_LOOPBACK(buff));
- buff[15] = 1;
- EXPECT_TRUE(IN6_IS_ADDR_LOOPBACK(buff));
- buff[15] = 0;
+ EXPECT_FALSE(IN6_IS_ADDR_LOOPBACK(&addr));
+ addr.s6_addr[15] = 1;
+ EXPECT_TRUE(IN6_IS_ADDR_LOOPBACK(&addr));
+ addr.s6_addr[15] = 0;
- EXPECT_FALSE(IN6_IS_ADDR_MULTICAST(buff));
- buff[0] = 0xff;
- EXPECT_TRUE(IN6_IS_ADDR_MULTICAST(buff));
- buff[0] = 0;
+ EXPECT_FALSE(IN6_IS_ADDR_MULTICAST(&addr));
+ addr.s6_addr[0] = 0xff;
+ EXPECT_TRUE(IN6_IS_ADDR_MULTICAST(&addr));
+ addr.s6_addr[0] = 0;
- buff[0] = 0xfe;
- buff[1] = 0x80;
- EXPECT_TRUE(IN6_IS_ADDR_LINKLOCAL(buff));
- buff[0] = 0xff;
- buff[1] = 0x80;
- EXPECT_FALSE(IN6_IS_ADDR_LINKLOCAL(buff));
+ addr.s6_addr[0] = 0xfe;
+ addr.s6_addr[1] = 0x80;
+ EXPECT_TRUE(IN6_IS_ADDR_LINKLOCAL(&addr));
+ addr.s6_addr[0] = 0xff;
+ addr.s6_addr[1] = 0x80;
+ EXPECT_FALSE(IN6_IS_ADDR_LINKLOCAL(&addr));
- buff[0] = 0xfe;
- buff[1] = 0xc0;
- EXPECT_TRUE(IN6_IS_ADDR_SITELOCAL(buff));
- buff[0] = 0xff;
- buff[1] = 0x80;
- EXPECT_FALSE(IN6_IS_ADDR_SITELOCAL(buff));
+ addr.s6_addr[0] = 0xfe;
+ addr.s6_addr[1] = 0xc0;
+ EXPECT_TRUE(IN6_IS_ADDR_SITELOCAL(&addr));
+ addr.s6_addr[0] = 0xff;
+ addr.s6_addr[1] = 0x80;
+ EXPECT_FALSE(IN6_IS_ADDR_SITELOCAL(&addr));
- buff[0] = 0xff;
- buff[1] = 0x1;
- EXPECT_TRUE(IN6_IS_ADDR_MC_NODELOCAL(buff));
- buff[1] = 0x2;
- EXPECT_TRUE(IN6_IS_ADDR_MC_LINKLOCAL(buff));
- buff[1] = 0x5;
- EXPECT_TRUE(IN6_IS_ADDR_MC_SITELOCAL(buff));
- buff[1] = 0x8;
- EXPECT_TRUE(IN6_IS_ADDR_MC_ORGLOCAL(buff));
- buff[1] = 0xe;
- EXPECT_TRUE(IN6_IS_ADDR_MC_GLOBAL(buff));
- buff[1] = 0;
- buff[0] = 0;
+ addr.s6_addr[0] = 0xff;
+ addr.s6_addr[1] = 0x1;
+ EXPECT_TRUE(IN6_IS_ADDR_MC_NODELOCAL(&addr));
+ addr.s6_addr[1] = 0x2;
+ EXPECT_TRUE(IN6_IS_ADDR_MC_LINKLOCAL(&addr));
+ addr.s6_addr[1] = 0x5;
+ EXPECT_TRUE(IN6_IS_ADDR_MC_SITELOCAL(&addr));
+ addr.s6_addr[1] = 0x8;
+ EXPECT_TRUE(IN6_IS_ADDR_MC_ORGLOCAL(&addr));
+ addr.s6_addr[1] = 0xe;
+ EXPECT_TRUE(IN6_IS_ADDR_MC_GLOBAL(&addr));
+ addr.s6_addr[1] = 0;
+ addr.s6_addr[0] = 0;
- EXPECT_FALSE(IN6_IS_ADDR_V4MAPPED(buff));
- buff[10] = 0xff;
- buff[11] = 0xff;
- EXPECT_TRUE(IN6_IS_ADDR_V4MAPPED(buff));
- buff[10] = 0;
- buff[11] = 0;
+ EXPECT_FALSE(IN6_IS_ADDR_V4MAPPED(&addr));
+ addr.s6_addr[10] = 0xff;
+ addr.s6_addr[11] = 0xff;
+ EXPECT_TRUE(IN6_IS_ADDR_V4MAPPED(&addr));
+ addr.s6_addr[10] = 0;
+ addr.s6_addr[11] = 0;
for (int i = 12; i < 16; ++i) {
- buff[i] ^= 42;
- EXPECT_TRUE(IN6_IS_ADDR_V4COMPAT(buff));
- buff[i] ^= 42;
+ addr.s6_addr[i] ^= 42;
+ EXPECT_TRUE(IN6_IS_ADDR_V4COMPAT(&addr));
+ addr.s6_addr[i] ^= 42;
}
for (int i = 0; i < 12; ++i) {
- buff[i] ^= 42;
- EXPECT_FALSE(IN6_IS_ADDR_V4COMPAT(buff));
- buff[i] ^= 42;
+ addr.s6_addr[i] ^= 42;
+ EXPECT_FALSE(IN6_IS_ADDR_V4COMPAT(&addr));
+ addr.s6_addr[i] ^= 42;
}
}
>From 9f1b3f9149d8a1d64c45978e11a6664799d155e6 Mon Sep 17 00:00:00 2001
From: Pavel Labath <pavel at labath.sk>
Date: Wed, 15 Jul 2026 14:48:04 +0000
Subject: [PATCH 2/2] format
---
libc/include/llvm-libc-macros/netinet-in-macros.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/libc/include/llvm-libc-macros/netinet-in-macros.h b/libc/include/llvm-libc-macros/netinet-in-macros.h
index d7c9d2d2a7e9c..1636736d3b26d 100644
--- a/libc/include/llvm-libc-macros/netinet-in-macros.h
+++ b/libc/include/llvm-libc-macros/netinet-in-macros.h
@@ -49,8 +49,8 @@
#define __IN6_IS_ADDR_LOOPBACK(a) \
((a)->s6_addr32[0] == 0 && (a)->s6_addr32[1] == 0 && \
- (a)->s6_addr32[2] == 0 && (a)->s6_addr[12] == 0 && \
- (a)->s6_addr[13] == 0 && (a)->s6_addr[14] == 0 && (a)->s6_addr[15] == 1)
+ (a)->s6_addr32[2] == 0 && (a)->s6_addr[12] == 0 && (a)->s6_addr[13] == 0 && \
+ (a)->s6_addr[14] == 0 && (a)->s6_addr[15] == 1)
#define IN6_IS_ADDR_UNSPECIFIED(a) \
(__extension__({ \
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