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* [PATCH v4 0/3] Switch get/put unaligned to use memcpy
@ 2025-07-22 21:57 Ian Rogers
  2025-07-22 21:57 ` [PATCH v4 1/3] vdso: Switch get/put unaligned from packed struct to memcpy Ian Rogers
                   ` (2 more replies)
  0 siblings, 3 replies; 9+ messages in thread
From: Ian Rogers @ 2025-07-22 21:57 UTC (permalink / raw)
  To: Eric Biggers, Yuzhuo Jing, Andy Lutomirski, Thomas Gleixner,
	Vincenzo Frascino, Arnaldo Carvalho de Melo, Al Viro,
	Christophe Leroy, Jason A. Donenfeld, linux-kernel,
	linux-perf-users
  Cc: Ian Rogers

The existing type punning approach with packed structs requires
 -fno-strict-aliasing to be passed to the compiler for
correctness. This is true in the kernel tree but not in the tools
directory resulting in this suggested patch from Eric Biggers
 <ebiggers@google.com>:
https://lore.kernel.org/lkml/20250625202311.23244-2-ebiggers@kernel.org/

Requiring -fno-strict-aliasing seems unfortunate and so this patch
makes the unaligned code work via memcpy for type punning rather than
the packed attribute.

v4: switch the type/expression variable __get_unaligned_ctrl_type that
    is used by _Generic to be a pointer to avoid 0 vs NULL usage
    warnings - always use NULL and dereference the type. This should
    also hopefully address analysis bots complaints.

v3: switch to __unqual_scalar_typeof, reducing the code, and use an
    uninitialized variable rather than a cast of 0 to try to avoid a
    sparse warning about not using NULL. The code is trying to
    navigate a minefield of uninitialized and casting warnings,
    hopefully the best balance has been struck, but the code will fail
    for cases like:
    const void *val = get_unaligned((const void * const *)ptr);
    due to __unqual_scalar_typeof leaving the 2nd const of the cast in
    place. Thankfully no code does this - tested with an
    allyesconfig. Support would be achievable by using void* as a
    default case in __unqual_scalar_typeof, it just doesn't seem worth
    it for a fairly unusual const case.

v2: switch memcpy to __builtin_memcpy to avoid potential/disallowed
    memcpy calls in vdso caused by -fno-builtin. Reported by
    Christophe Leroy <christophe.leroy@csgroup.eu>:
    https://lore.kernel.org/lkml/c57de5bf-d55c-48c5-9dfa-e2fb844dafe9@csgroup.eu/

Ian Rogers (3):
  vdso: Switch get/put unaligned from packed struct to memcpy
  tools headers: Update the linux/unaligned.h copy with the kernel
    sources
  tools headers: Remove unneeded ignoring of warnings in unaligned.h

 include/vdso/unaligned.h             | 41 ++++++++++++++++++++++++----
 tools/include/linux/compiler_types.h | 22 +++++++++++++++
 tools/include/linux/unaligned.h      |  4 ---
 tools/include/vdso/unaligned.h       | 41 ++++++++++++++++++++++++----
 4 files changed, 92 insertions(+), 16 deletions(-)

-- 
2.50.0.727.gbf7dc18ff4-goog


^ permalink raw reply	[flat|nested] 9+ messages in thread
* [PATCH v5 4/4] tools headers: Remove unneeded ignoring of warnings in unaligned.h
@ 2025-10-16 20:51 Ian Rogers
  2026-01-13 13:47 ` [tip: timers/vdso] " tip-bot2 for Ian Rogers
  2026-01-14  8:01 ` tip-bot2 for Ian Rogers
  0 siblings, 2 replies; 9+ messages in thread
From: Ian Rogers @ 2025-10-16 20:51 UTC (permalink / raw)
  To: James E.J. Bottomley, Helge Deller, Andy Lutomirski,
	Thomas Gleixner, Vincenzo Frascino, Ian Rogers,
	Arnaldo Carvalho de Melo, linux-parisc, linux-kernel,
	Eric Biggers, Al Viro, Christophe Leroy, Jason A. Donenfeld

Now the get/put unaligned use memcpy the -Wpacked and -Wattributes
warnings don't need disabling.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/include/linux/unaligned.h | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/tools/include/linux/unaligned.h b/tools/include/linux/unaligned.h
index 395a4464fe73..d51ddafed138 100644
--- a/tools/include/linux/unaligned.h
+++ b/tools/include/linux/unaligned.h
@@ -6,9 +6,6 @@
  * This is the most generic implementation of unaligned accesses
  * and should work almost anywhere.
  */
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wpacked"
-#pragma GCC diagnostic ignored "-Wattributes"
 #include <vdso/unaligned.h>
 
 #define get_unaligned(ptr)	__get_unaligned_t(typeof(*(ptr)), (ptr))
@@ -143,6 +140,5 @@ static inline u64 get_unaligned_be48(const void *p)
 {
 	return __get_unaligned_be48(p);
 }
-#pragma GCC diagnostic pop
 
 #endif /* __LINUX_UNALIGNED_H */
-- 
2.51.0.858.gf9c4a03a3a-goog


^ permalink raw reply	[flat|nested] 9+ messages in thread

end of thread, other threads:[~2026-01-14  8:01 UTC | newest]

Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2025-07-22 21:57 [PATCH v4 0/3] Switch get/put unaligned to use memcpy Ian Rogers
2025-07-22 21:57 ` [PATCH v4 1/3] vdso: Switch get/put unaligned from packed struct to memcpy Ian Rogers
2025-09-04  9:48   ` [tip: timers/vdso] vdso: Switch get/put_unaligned() from packed struct to memcpy() tip-bot2 for Ian Rogers
2025-07-22 21:57 ` [PATCH v4 2/3] tools headers: Update the linux/unaligned.h copy with the kernel sources Ian Rogers
2025-09-04  9:48   ` [tip: timers/vdso] " tip-bot2 for Ian Rogers
2025-07-22 21:57 ` [PATCH v4 3/3] tools headers: Remove unneeded ignoring of warnings in unaligned.h Ian Rogers
2025-09-04  9:48   ` [tip: timers/vdso] " tip-bot2 for Ian Rogers
2025-10-16 20:51 [PATCH v5 4/4] " Ian Rogers
2026-01-13 13:47 ` [tip: timers/vdso] " tip-bot2 for Ian Rogers
2026-01-14  8:01 ` tip-bot2 for Ian Rogers

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