Backports of d0afcfeb9e3810ec89d1ffde1a0e36621bb75dca for 6.6 and older

Hi Greg and Sasha,

Please find attached backports of commit d0afcfeb9e38 ("kbuild: Disable -Wdefault-const-init-unsafe") for 6.6 and older, which is needed for tip of tree versions of LLVM. Please let me know if there are any questions.

Cheers,
Nathan

From 163300e375a1e1809ea72c348d6a78026d365731 Mon Sep 17 00:00:00 2001
From: Nathan Chancellor <[email protected]>
Date: Tue, 6 May 2025 14:02:01 -0700
Subject: [PATCH 5.4] kbuild: Disable -Wdefault-const-init-unsafe

commit d0afcfeb9e3810ec89d1ffde1a0e36621bb75dca upstream.

A new on by default warning in clang [1] aims to flags instances where const variables without static or thread local storage or const members in aggregate types are not initialized because it can lead to an indeterminate value. This is quite noisy for the kernel due to instances originating from header files such as:

drivers/gpu/drm/i915/gt/intel_ring.h:62:2: error: default initialization of an object of type 'typeof (ring->size)' (aka 'const unsigned int') leaves the object uninitialized [-Werror,-Wdefault-const-init-var-unsafe]

     62 |         typecheck(typeof(ring->size), next);
        |         ^
  include/linux/typecheck.h:10:9: note: expanded from macro 'typecheck'
     10 | ({      type __dummy; \
        |              ^

  include/net/ip.h:478:14: error: default initialization of an object of type 'typeof (rt->dst.expires)' (aka 'const unsigned long') leaves the object uninitialized [-Werror,-Wdefault-const-init-var-unsafe]
    478 |                 if (mtu && time_before(jiffies, rt->dst.expires))
        |                            ^
  include/linux/jiffies.h:138:26: note: expanded from macro 'time_before'
    138 | #define time_before(a,b)        time_after(b,a)
        |                                 ^
  include/linux/jiffies.h:128:3: note: expanded from macro 'time_after'
    128 |         (typecheck(unsigned long, a) && \
        |          ^
  include/linux/typecheck.h:11:12: note: expanded from macro 'typecheck'
     11 |         typeof(x) __dummy2; \
        |                   ^

include/linux/list.h:409:27: warning: default initialization of an object of type 'union (unnamed union at include/linux/list.h:409:27)' with const member leaves the object uninitialized [-Wdefault-const-init-field-unsafe]

    409 |         struct list_head *next = smp_load_acquire(&head->next);
        |                                  ^
  include/asm-generic/barrier.h:176:29: note: expanded from macro 'smp_load_acquire'
    176 | #define smp_load_acquire(p) __smp_load_acquire(p)
        |                             ^
  arch/arm64/include/asm/barrier.h:164:59: note: expanded from macro '__smp_load_acquire'
    164 |         union { __unqual_scalar_typeof(*p) __val; char __c[1]; } __u;   \
        |                                                                  ^

include/linux/list.h:409:27: note: member '__val' declared 'const' here

crypto/scatterwalk.c:66:22: error: default initialization of an object of type 'struct scatter_walk' with const member leaves the object uninitialized [-Werror,-Wdefault-const-init-field-unsafe]

     66 |         struct scatter_walk walk;
        |                             ^
  include/crypto/algapi.h:112:15: note: member 'addr' declared 'const' here
    112 |                 void *const addr;
        |                             ^

fs/hugetlbfs/inode.c:733:24: error: default initialization of an object of type 'struct vm_area_struct' with const member leaves the object uninitialized [-Werror,-Wdefault-const-init-field-unsafe]

    733 |         struct vm_area_struct pseudo_vma;
        |                               ^
  include/linux/mm_types.h:803:20: note: member 'vm_flags' declared 'const' here
    803 |                 const vm_flags_t vm_flags;
        |                                  ^

Silencing the instances from typecheck.h is difficult because '= {}' is not available in older but supported compilers and '= {0}' would cause warnings about a literal 0 being treated as NULL. While it might be possible to come up with a local hack to silence the warning for clang-21+, it may not be worth it since -Wuninitialized will still trigger if an uninitialized const variable is actually used.

In all audited cases of the "field" variant of the warning, the members are either not used in the particular call path, modified through other means such as memset() / memcpy() because the containing object is not const, or are within a union with other non-const members.

Since this warning does not appear to have a high signal to noise ratio, just disable it.

[nathan: Apply change to Makefile instead of scripts/Makefile.extrawarn
due to lack of e88ca24319e4 in older stable branches]

---
 Makefile | 12 ++++++++++++
 1 file changed, 12 insertions(+)

index 70d2e8cc6f9f..55b6f6bbc4f5 100644
@@ -770,6 +770,18 @@ KBUILD_CFLAGS += -Wno-tautological-compare
 # source of a reference will be _MergedGlobals and not on of the whitelisted names.
 # See modpost pattern 2
 KBUILD_CFLAGS += -mno-global-merge
+
+# Clang may emit a warning when a const variable, such as the dummy variables
+# in typecheck(), or const member of an aggregate type are not initialized,
+# which can result in unexpected behavior. However, in many audited cases of
+# the "field" variant of the warning, this is intentional because the field is
+# never used within a particular call path, the field is within a union with
+# other non-const members, or the containing object is not const so the field
+# can be modified via memcpy() / memset(). While the variable warning also gets
+# disabled with this same switch, there should not be too much coverage lost
+# because -Wuninitialized will still flag when an uninitialized const variable
+# is used.
+KBUILD_CFLAGS += $(call cc-disable-warning, default-const-init-unsafe)
 else
 
 # Warn about unmarked fall-throughs in switch statement.

base-commit: 2c8115e4757809ffd537ed9108da115026d3581f

2.49.0

From 3b25f5705a71b11c73c3bb0e8cbe2bfa10a0a58a Mon Sep 17 00:00:00 2001
From: Nathan Chancellor <[email protected]>
Date: Tue, 6 May 2025 14:02:01 -0700
Subject: [PATCH 5.10] kbuild: Disable -Wdefault-const-init-unsafe

commit d0afcfeb9e3810ec89d1ffde1a0e36621bb75dca upstream.

A new on by default warning in clang [1] aims to flags instances where const variables without static or thread local storage or const members in aggregate types are not initialized because it can lead to an indeterminate value. This is quite noisy for the kernel due to instances originating from header files such as:

drivers/gpu/drm/i915/gt/intel_ring.h:62:2: error: default initialization of an object of type 'typeof (ring->size)' (aka 'const unsigned int') leaves the object uninitialized [-Werror,-Wdefault-const-init-var-unsafe]

     62 |         typecheck(typeof(ring->size), next);
        |         ^
  include/linux/typecheck.h:10:9: note: expanded from macro 'typecheck'
     10 | ({      type __dummy; \
        |              ^

  include/net/ip.h:478:14: error: default initialization of an object of type 'typeof (rt->dst.expires)' (aka 'const unsigned long') leaves the object uninitialized [-Werror,-Wdefault-const-init-var-unsafe]
    478 |                 if (mtu && time_before(jiffies, rt->dst.expires))
        |                            ^
  include/linux/jiffies.h:138:26: note: expanded from macro 'time_before'
    138 | #define time_before(a,b)        time_after(b,a)
        |                                 ^
  include/linux/jiffies.h:128:3: note: expanded from macro 'time_after'
    128 |         (typecheck(unsigned long, a) && \
        |          ^
  include/linux/typecheck.h:11:12: note: expanded from macro 'typecheck'
     11 |         typeof(x) __dummy2; \
        |                   ^

include/linux/list.h:409:27: warning: default initialization of an object of type 'union (unnamed union at include/linux/list.h:409:27)' with const member leaves the object uninitialized [-Wdefault-const-init-field-unsafe]

    409 |         struct list_head *next = smp_load_acquire(&head->next);
        |                                  ^
  include/asm-generic/barrier.h:176:29: note: expanded from macro 'smp_load_acquire'
    176 | #define smp_load_acquire(p) __smp_load_acquire(p)
        |                             ^
  arch/arm64/include/asm/barrier.h:164:59: note: expanded from macro '__smp_load_acquire'
    164 |         union { __unqual_scalar_typeof(*p) __val; char __c[1]; } __u;   \
        |                                                                  ^

include/linux/list.h:409:27: note: member '__val' declared 'const' here

crypto/scatterwalk.c:66:22: error: default initialization of an object of type 'struct scatter_walk' with const member leaves the object uninitialized [-Werror,-Wdefault-const-init-field-unsafe]

     66 |         struct scatter_walk walk;
        |                             ^
  include/crypto/algapi.h:112:15: note: member 'addr' declared 'const' here
    112 |                 void *const addr;
        |                             ^

fs/hugetlbfs/inode.c:733:24: error: default initialization of an object of type 'struct vm_area_struct' with const member leaves the object uninitialized [-Werror,-Wdefault-const-init-field-unsafe]

    733 |         struct vm_area_struct pseudo_vma;
        |                               ^
  include/linux/mm_types.h:803:20: note: member 'vm_flags' declared 'const' here
    803 |                 const vm_flags_t vm_flags;
        |                                  ^

Silencing the instances from typecheck.h is difficult because '= {}' is not available in older but supported compilers and '= {0}' would cause warnings about a literal 0 being treated as NULL. While it might be possible to come up with a local hack to silence the warning for clang-21+, it may not be worth it since -Wuninitialized will still trigger if an uninitialized const variable is actually used.

In all audited cases of the "field" variant of the warning, the members are either not used in the particular call path, modified through other means such as memset() / memcpy() because the containing object is not const, or are within a union with other non-const members.

Since this warning does not appear to have a high signal to noise ratio, just disable it.

[nathan: Apply change to Makefile instead of scripts/Makefile.extrawarn
due to lack of e88ca24319e4 in older stable branches]

---
 Makefile | 12 ++++++++++++
 1 file changed, 12 insertions(+)

index b0e2f455eb87..4687dae9cd82 100644
@@ -795,6 +795,18 @@ KBUILD_CFLAGS += -Wno-gnu
 # source of a reference will be _MergedGlobals and not on of the whitelisted names.
 # See modpost pattern 2
 KBUILD_CFLAGS += -mno-global-merge
+
+# Clang may emit a warning when a const variable, such as the dummy variables
+# in typecheck(), or const member of an aggregate type are not initialized,
+# which can result in unexpected behavior. However, in many audited cases of
+# the "field" variant of the warning, this is intentional because the field is
+# never used within a particular call path, the field is within a union with
+# other non-const members, or the containing object is not const so the field
+# can be modified via memcpy() / memset(). While the variable warning also gets
+# disabled with this same switch, there should not be too much coverage lost
+# because -Wuninitialized will still flag when an uninitialized const variable
+# is used.
+KBUILD_CFLAGS += $(call cc-disable-warning, default-const-init-unsafe)
 else
 
 # Warn about unmarked fall-throughs in switch statement.

base-commit: 024a4a45fdf87218e3c0925475b05a27bcea103f

2.49.0

From 0e0cf9509b6e754fbf7bf45524292c17c9e4b64b Mon Sep 17 00:00:00 2001
From: Nathan Chancellor <[email protected]>
Date: Tue, 6 May 2025 14:02:01 -0700
Subject: [PATCH 5.15] kbuild: Disable -Wdefault-const-init-unsafe

commit d0afcfeb9e3810ec89d1ffde1a0e36621bb75dca upstream.

A new on by default warning in clang [1] aims to flags instances where const variables without static or thread local storage or const members in aggregate types are not initialized because it can lead to an indeterminate value. This is quite noisy for the kernel due to instances originating from header files such as:

drivers/gpu/drm/i915/gt/intel_ring.h:62:2: error: default initialization of an object of type 'typeof (ring->size)' (aka 'const unsigned int') leaves the object uninitialized [-Werror,-Wdefault-const-init-var-unsafe]

     62 |         typecheck(typeof(ring->size), next);
        |         ^
  include/linux/typecheck.h:10:9: note: expanded from macro 'typecheck'
     10 | ({      type __dummy; \
        |              ^

  include/net/ip.h:478:14: error: default initialization of an object of type 'typeof (rt->dst.expires)' (aka 'const unsigned long') leaves the object uninitialized [-Werror,-Wdefault-const-init-var-unsafe]
    478 |                 if (mtu && time_before(jiffies, rt->dst.expires))
        |                            ^
  include/linux/jiffies.h:138:26: note: expanded from macro 'time_before'
    138 | #define time_before(a,b)        time_after(b,a)
        |                                 ^
  include/linux/jiffies.h:128:3: note: expanded from macro 'time_after'
    128 |         (typecheck(unsigned long, a) && \
        |          ^
  include/linux/typecheck.h:11:12: note: expanded from macro 'typecheck'
     11 |         typeof(x) __dummy2; \
        |                   ^

include/linux/list.h:409:27: warning: default initialization of an object of type 'union (unnamed union at include/linux/list.h:409:27)' with const member leaves the object uninitialized [-Wdefault-const-init-field-unsafe]

    409 |         struct list_head *next = smp_load_acquire(&head->next);
        |                                  ^
  include/asm-generic/barrier.h:176:29: note: expanded from macro 'smp_load_acquire'
    176 | #define smp_load_acquire(p) __smp_load_acquire(p)
        |                             ^
  arch/arm64/include/asm/barrier.h:164:59: note: expanded from macro '__smp_load_acquire'
    164 |         union { __unqual_scalar_typeof(*p) __val; char __c[1]; } __u;   \
        |                                                                  ^

include/linux/list.h:409:27: note: member '__val' declared 'const' here

crypto/scatterwalk.c:66:22: error: default initialization of an object of type 'struct scatter_walk' with const member leaves the object uninitialized [-Werror,-Wdefault-const-init-field-unsafe]

     66 |         struct scatter_walk walk;
        |                             ^
  include/crypto/algapi.h:112:15: note: member 'addr' declared 'const' here
    112 |                 void *const addr;
        |                             ^

fs/hugetlbfs/inode.c:733:24: error: default initialization of an object of type 'struct vm_area_struct' with const member leaves the object uninitialized [-Werror,-Wdefault-const-init-field-unsafe]

    733 |         struct vm_area_struct pseudo_vma;
        |                               ^
  include/linux/mm_types.h:803:20: note: member 'vm_flags' declared 'const' here
    803 |                 const vm_flags_t vm_flags;
        |                                  ^

Silencing the instances from typecheck.h is difficult because '= {}' is not available in older but supported compilers and '= {0}' would cause warnings about a literal 0 being treated as NULL. While it might be possible to come up with a local hack to silence the warning for clang-21+, it may not be worth it since -Wuninitialized will still trigger if an uninitialized const variable is actually used.

In all audited cases of the "field" variant of the warning, the members are either not used in the particular call path, modified through other means such as memset() / memcpy() because the containing object is not const, or are within a union with other non-const members.

Since this warning does not appear to have a high signal to noise ratio, just disable it.

[nathan: Apply change to Makefile instead of scripts/Makefile.extrawarn
due to lack of e88ca24319e4 in older stable branches]

---
 Makefile | 12 ++++++++++++
 1 file changed, 12 insertions(+)

index 0840259608be..2894ed66c4e5 100644
@@ -814,6 +814,18 @@ KBUILD_CFLAGS += -Wno-gnu
 # source of a reference will be _MergedGlobals and not on of the whitelisted names.
 # See modpost pattern 2
 KBUILD_CFLAGS += -mno-global-merge
+
+# Clang may emit a warning when a const variable, such as the dummy variables
+# in typecheck(), or const member of an aggregate type are not initialized,
+# which can result in unexpected behavior. However, in many audited cases of
+# the "field" variant of the warning, this is intentional because the field is
+# never used within a particular call path, the field is within a union with
+# other non-const members, or the containing object is not const so the field
+# can be modified via memcpy() / memset(). While the variable warning also gets
+# disabled with this same switch, there should not be too much coverage lost
+# because -Wuninitialized will still flag when an uninitialized const variable
+# is used.
+KBUILD_CFLAGS += $(call cc-disable-warning, default-const-init-unsafe)
 else
 
 # Warn about unmarked fall-throughs in switch statement.

base-commit: 98f47d0e9b8c557d3063d3ea661cbea1489af330

2.49.0

From 76144f38354290f26ec39f139464bd48409815b9 Mon Sep 17 00:00:00 2001
From: Nathan Chancellor <[email protected]>
Date: Tue, 6 May 2025 14:02:01 -0700
Subject: [PATCH 6.1] kbuild: Disable -Wdefault-const-init-unsafe

commit d0afcfeb9e3810ec89d1ffde1a0e36621bb75dca upstream.

A new on by default warning in clang [1] aims to flags instances where const variables without static or thread local storage or const members in aggregate types are not initialized because it can lead to an indeterminate value. This is quite noisy for the kernel due to instances originating from header files such as:

drivers/gpu/drm/i915/gt/intel_ring.h:62:2: error: default initialization of an object of type 'typeof (ring->size)' (aka 'const unsigned int') leaves the object uninitialized [-Werror,-Wdefault-const-init-var-unsafe]

     62 |         typecheck(typeof(ring->size), next);
        |         ^
  include/linux/typecheck.h:10:9: note: expanded from macro 'typecheck'
     10 | ({      type __dummy; \
        |              ^

  include/net/ip.h:478:14: error: default initialization of an object of type 'typeof (rt->dst.expires)' (aka 'const unsigned long') leaves the object uninitialized [-Werror,-Wdefault-const-init-var-unsafe]
    478 |                 if (mtu && time_before(jiffies, rt->dst.expires))
        |                            ^
  include/linux/jiffies.h:138:26: note: expanded from macro 'time_before'
    138 | #define time_before(a,b)        time_after(b,a)
        |                                 ^
  include/linux/jiffies.h:128:3: note: expanded from macro 'time_after'
    128 |         (typecheck(unsigned long, a) && \
        |          ^
  include/linux/typecheck.h:11:12: note: expanded from macro 'typecheck'
     11 |         typeof(x) __dummy2; \
        |                   ^

include/linux/list.h:409:27: warning: default initialization of an object of type 'union (unnamed union at include/linux/list.h:409:27)' with const member leaves the object uninitialized [-Wdefault-const-init-field-unsafe]

    409 |         struct list_head *next = smp_load_acquire(&head->next);
        |                                  ^
  include/asm-generic/barrier.h:176:29: note: expanded from macro 'smp_load_acquire'
    176 | #define smp_load_acquire(p) __smp_load_acquire(p)
        |                             ^
  arch/arm64/include/asm/barrier.h:164:59: note: expanded from macro '__smp_load_acquire'
    164 |         union { __unqual_scalar_typeof(*p) __val; char __c[1]; } __u;   \
        |                                                                  ^

include/linux/list.h:409:27: note: member '__val' declared 'const' here

crypto/scatterwalk.c:66:22: error: default initialization of an object of type 'struct scatter_walk' with const member leaves the object uninitialized [-Werror,-Wdefault-const-init-field-unsafe]

     66 |         struct scatter_walk walk;
        |                             ^
  include/crypto/algapi.h:112:15: note: member 'addr' declared 'const' here
    112 |                 void *const addr;
        |                             ^

fs/hugetlbfs/inode.c:733:24: error: default initialization of an object of type 'struct vm_area_struct' with const member leaves the object uninitialized [-Werror,-Wdefault-const-init-field-unsafe]

    733 |         struct vm_area_struct pseudo_vma;
        |                               ^
  include/linux/mm_types.h:803:20: note: member 'vm_flags' declared 'const' here
    803 |                 const vm_flags_t vm_flags;
        |                                  ^

Silencing the instances from typecheck.h is difficult because '= {}' is not available in older but supported compilers and '= {0}' would cause warnings about a literal 0 being treated as NULL. While it might be possible to come up with a local hack to silence the warning for clang-21+, it may not be worth it since -Wuninitialized will still trigger if an uninitialized const variable is actually used.

In all audited cases of the "field" variant of the warning, the members are either not used in the particular call path, modified through other means such as memset() / memcpy() because the containing object is not const, or are within a union with other non-const members.

Since this warning does not appear to have a high signal to noise ratio, just disable it.

[nathan: Apply change to Makefile instead of scripts/Makefile.extrawarn
due to lack of e88ca24319e4 in older stable branches]

---
 Makefile | 12 ++++++++++++
 1 file changed, 12 insertions(+)

index f86e26fa0b31..9a7bc4372e35 100644
@@ -875,6 +875,18 @@ ifdef CONFIG_CC_IS_CLANG
 KBUILD_CPPFLAGS += -Qunused-arguments
 # The kernel builds with '-std=gnu11' so use of GNU extensions is acceptable.
 KBUILD_CFLAGS += -Wno-gnu
+
+# Clang may emit a warning when a const variable, such as the dummy variables
+# in typecheck(), or const member of an aggregate type are not initialized,
+# which can result in unexpected behavior. However, in many audited cases of
+# the "field" variant of the warning, this is intentional because the field is
+# never used within a particular call path, the field is within a union with
+# other non-const members, or the containing object is not const so the field
+# can be modified via memcpy() / memset(). While the variable warning also gets
+# disabled with this same switch, there should not be too much coverage lost
+# because -Wuninitialized will still flag when an uninitialized const variable
+# is used.
+KBUILD_CFLAGS += $(call cc-disable-warning, default-const-init-unsafe)
 else
 
 # gcc inanely warns about local variables called 'main'

base-commit: da3c5173c55f7a0cf65c967d864386c79dcba3f7

2.49.0

From 42684bf0c008808893c873f57246c6e2b3cb57c8 Mon Sep 17 00:00:00 2001
From: Nathan Chancellor <[email protected]>
Date: Tue, 6 May 2025 14:02:01 -0700
Subject: [PATCH 6.6] kbuild: Disable -Wdefault-const-init-unsafe

commit d0afcfeb9e3810ec89d1ffde1a0e36621bb75dca upstream.

A new on by default warning in clang [1] aims to flags instances where const variables without static or thread local storage or const members in aggregate types are not initialized because it can lead to an indeterminate value. This is quite noisy for the kernel due to instances originating from header files such as:

drivers/gpu/drm/i915/gt/intel_ring.h:62:2: error: default initialization of an object of type 'typeof (ring->size)' (aka 'const unsigned int') leaves the object uninitialized [-Werror,-Wdefault-const-init-var-unsafe]

     62 |         typecheck(typeof(ring->size), next);
        |         ^
  include/linux/typecheck.h:10:9: note: expanded from macro 'typecheck'
     10 | ({      type __dummy; \
        |              ^

  include/net/ip.h:478:14: error: default initialization of an object of type 'typeof (rt->dst.expires)' (aka 'const unsigned long') leaves the object uninitialized [-Werror,-Wdefault-const-init-var-unsafe]
    478 |                 if (mtu && time_before(jiffies, rt->dst.expires))
        |                            ^
  include/linux/jiffies.h:138:26: note: expanded from macro 'time_before'
    138 | #define time_before(a,b)        time_after(b,a)
        |                                 ^
  include/linux/jiffies.h:128:3: note: expanded from macro 'time_after'
    128 |         (typecheck(unsigned long, a) && \
        |          ^
  include/linux/typecheck.h:11:12: note: expanded from macro 'typecheck'
     11 |         typeof(x) __dummy2; \
        |                   ^

include/linux/list.h:409:27: warning: default initialization of an object of type 'union (unnamed union at include/linux/list.h:409:27)' with const member leaves the object uninitialized [-Wdefault-const-init-field-unsafe]

    409 |         struct list_head *next = smp_load_acquire(&head->next);
        |                                  ^
  include/asm-generic/barrier.h:176:29: note: expanded from macro 'smp_load_acquire'
    176 | #define smp_load_acquire(p) __smp_load_acquire(p)
        |                             ^
  arch/arm64/include/asm/barrier.h:164:59: note: expanded from macro '__smp_load_acquire'
    164 |         union { __unqual_scalar_typeof(*p) __val; char __c[1]; } __u;   \
        |                                                                  ^

include/linux/list.h:409:27: note: member '__val' declared 'const' here

crypto/scatterwalk.c:66:22: error: default initialization of an object of type 'struct scatter_walk' with const member leaves the object uninitialized [-Werror,-Wdefault-const-init-field-unsafe]

     66 |         struct scatter_walk walk;
        |                             ^
  include/crypto/algapi.h:112:15: note: member 'addr' declared 'const' here
    112 |                 void *const addr;
        |                             ^

fs/hugetlbfs/inode.c:733:24: error: default initialization of an object of type 'struct vm_area_struct' with const member leaves the object uninitialized [-Werror,-Wdefault-const-init-field-unsafe]

    733 |         struct vm_area_struct pseudo_vma;
        |                               ^
  include/linux/mm_types.h:803:20: note: member 'vm_flags' declared 'const' here
    803 |                 const vm_flags_t vm_flags;
        |                                  ^

Silencing the instances from typecheck.h is difficult because '= {}' is not available in older but supported compilers and '= {0}' would cause warnings about a literal 0 being treated as NULL. While it might be possible to come up with a local hack to silence the warning for clang-21+, it may not be worth it since -Wuninitialized will still trigger if an uninitialized const variable is actually used.

In all audited cases of the "field" variant of the warning, the members are either not used in the particular call path, modified through other means such as memset() / memcpy() because the containing object is not const, or are within a union with other non-const members.

Since this warning does not appear to have a high signal to noise ratio, just disable it.

---
 scripts/Makefile.extrawarn | 12 ++++++++++++
 1 file changed, 12 insertions(+)

index 0ea3281a92e1..570f64e2ddf1 100644
@@ -29,6 +29,18 @@ KBUILD_CFLAGS-$(CONFIG_CC_NO_ARRAY_BOUNDS) += -Wno-array-bounds
 ifdef CONFIG_CC_IS_CLANG
 # The kernel builds with '-std=gnu11' so use of GNU extensions is acceptable.
 KBUILD_CFLAGS += -Wno-gnu
+
+# Clang may emit a warning when a const variable, such as the dummy variables
+# in typecheck(), or const member of an aggregate type are not initialized,
+# which can result in unexpected behavior. However, in many audited cases of
+# the "field" variant of the warning, this is intentional because the field is
+# never used within a particular call path, the field is within a union with
+# other non-const members, or the containing object is not const so the field
+# can be modified via memcpy() / memset(). While the variable warning also gets
+# disabled with this same switch, there should not be too much coverage lost
+# because -Wuninitialized will still flag when an uninitialized const variable
+# is used.
+KBUILD_CFLAGS += $(call cc-disable-warning, default-const-init-unsafe)
 else
 
 # gcc inanely warns about local variables called 'main'

base-commit: ffaf6178137b9cdcc9742d6677b70be164dfeb8c

2.49.0

All now queued up, thanks!

greg k-h

Hi Greg,

It looks like the 6.6 backport got lost?

  $ rg d0afcfeb9e3810ec89d1ffde1a0e36621bb75dca
  releases/6.1.141/kbuild-disable-wdefault-const-init-unsafe.patch:commit d0afcfeb9e3810ec89d1ffde1a0e36621bb75dca upstream.
  releases/5.4.294/kbuild-disable-wdefault-const-init-unsafe.patch:commit d0afcfeb9e3810ec89d1ffde1a0e36621bb75dca upstream.
  releases/5.15.185/kbuild-disable-wdefault-const-init-unsafe.patch:commit d0afcfeb9e3810ec89d1ffde1a0e36621bb75dca upstream.
  releases/5.10.238/kbuild-disable-wdefault-const-init-unsafe.patch:commit d0afcfeb9e3810ec89d1ffde1a0e36621bb75dca upstream.
  releases/6.14.8/kbuild-disable-wdefault-const-init-unsafe.patch:From d0afcfeb9e3810ec89d1ffde1a0e36621bb75dca Mon Sep 17 00:00:00 2001
  releases/6.14.8/kbuild-disable-wdefault-const-init-unsafe.patch:commit d0afcfeb9e3810ec89d1ffde1a0e36621bb75dca upstream.
  releases/6.12.30/kbuild-disable-wdefault-const-init-unsafe.patch:From d0afcfeb9e3810ec89d1ffde1a0e36621bb75dca Mon Sep 17 00:00:00 2001
  releases/6.12.30/kbuild-disable-wdefault-const-init-unsafe.patch:commit d0afcfeb9e3810ec89d1ffde1a0e36621bb75dca upstream.

Are you able to pull it from the original message? It still applies cleanly for me.

Cheers,
Nathan

Odd, it did not apply cleanly at all for me. I've hand-applied it now, thanks for catching this.

greg k-h