On 2/14/22 11:56 AM, Christophe Leroy wrote:
> While building a small config with CONFIG_CC_OPTIMISE_FOR_SIZE,
> I ended up with more than 50 times the following function in vmlinux
> because GCC doesn't honor the 'inline' keyword:
>
> c00243bc <copy_overflow>:
> c00243bc: 94 21 ff f0 stwu r1,-16(r1)
> c00243c0: 7c 85 23 78 mr r5,r4
> c00243c4: 7c 64 1b 78 mr r4,r3
> c00243c8: 3c 60 c0 62 lis r3,-16286
> c00243cc: 7c 08 02 a6 mflr r0
> c00243d0: 38 63 5e e5 addi r3,r3,24293
> c00243d4: 90 01 00 14 stw r0,20(r1)
> c00243d8: 4b ff 82 45 bl c001c61c <__warn_printk>
> c00243dc: 0f e0 00 00 twui r0,0
> c00243e0: 80 01 00 14 lwz r0,20(r1)
> c00243e4: 38 21 00 10 addi r1,r1,16
> c00243e8: 7c 08 03 a6 mtlr r0
> c00243ec: 4e 80 00 20 blr
>
> With -Winline, GCC tells:
>
> /include/linux/thread_info.h:212:20: warning: inlining failed in call to 'copy_overflow': call is unlikely and code size would grow [-Winline]
>
> copy_overflow() is a non conditional warning called by
> check_copy_size() on an error path.
>
> check_copy_size() have to remain inlined in order to benefit
> from constant folding, but copy_overflow() is not worth inlining.
>
> Uninline the warning when CONFIG_BUG is selected.
>
> When CONFIG_BUG is not selected, WARN() does nothing so skip it.
>
> This reduces the size of vmlinux by almost 4kbytes.
Just wondering, is this the only such scenario which results in
an avoidable bloated vmlinux image ?
>
> Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> ---
> v6: I should have gone sleeping yesterday night instead of sending v5 out. Sorry for the noise. Fix EXPORT_SYMBOL()
>
> v5: Change to EXPORT_SYMBOL() instead of EXPORT_SYMBOL_GPL()
>
> v4: Make copy_overflow() a no-op when CONFIG_BUG is not selected
>
> v3: Added missing ; after EXPORT_SYMBOL()
>
> v2: Added missing EXPORT_SYMBOL() and enhanced commit message
> ---
> include/linux/thread_info.h | 5 ++++-
> mm/maccess.c | 6 ++++++
> 2 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
> index 73a6f34b3847..9f392ec76f2b 100644
> --- a/include/linux/thread_info.h
> +++ b/include/linux/thread_info.h
> @@ -209,9 +209,12 @@ __bad_copy_from(void);
> extern void __compiletime_error("copy destination size is too small")
> __bad_copy_to(void);
>
> +void __copy_overflow(int size, unsigned long count);
> +
> static inline void copy_overflow(int size, unsigned long count)
> {
> - WARN(1, "Buffer overflow detected (%d < %lu)!\n", size, count);
> + if (IS_ENABLED(CONFIG_BUG))
> + __copy_overflow(size, count);
> }
>
> static __always_inline __must_check bool
> diff --git a/mm/maccess.c b/mm/maccess.c
> index d3f1a1f0b1c1..3fed2b876539 100644
> --- a/mm/maccess.c
> +++ b/mm/maccess.c
> @@ -335,3 +335,9 @@ long strnlen_user_nofault(const void __user *unsafe_addr, long count)
>
> return ret;
> }
> +
> +void __copy_overflow(int size, unsigned long count)
> +{
> + WARN(1, "Buffer overflow detected (%d < %lu)!\n", size, count);
> +}
> +EXPORT_SYMBOL(__copy_overflow);
>
