Re: [PATCH v8 4/4] arm64: vdso32: Implement __vdso_futex_robust_try_unlock()

["André Almeida" <andrealmeid@igalia.com>]

Em 16/09/2026 11:28, Mark Rutland escreveu:
> On Fri, Aug 21, 2026 at 06:50:45PM -0300, André Almeida wrote:
>> Based on aarch64 implementation, provide a 32 bit entry point for
>> this vDSO.
>>
>> In order to keep compatibility with arm64_futex_robust_unlock_get_pop(),
>> make sure to store the pop address at r2 and the compare result value
>> at r3.
> 
> Before we add this to the compat vdso, we'll need to implement this on
> arch/arm/.
> 
> Otherwise, my comments on the patch for the native vdso functions apply
> here too.
> 

Right, and the compat entry point at arch/arm64/ would point to the 
__vdso_futex_robust_list32_try_unlock implementation at arch/arm/?

> Mark.
> 
>>
>> Signed-off-by: André Almeida <andrealmeid@igalia.com>
>> ---
>> v7:
>>   - The store needs to be a release store, so s/strex/stlex/
>>   - result reg clobber modified to "=&r" to make sure the compiler don't use
>>   the r3 reg for something else
>>   - pop_reg will be read after the execution so it should be an output
>>   parameter with "+Q"
>> ---
>>   arch/arm64/kernel/vdso.c            | 15 ++++++++++++++-
>>   arch/arm64/kernel/vdso32/Makefile   |  4 ++++
>>   arch/arm64/kernel/vdso32/vdso.lds.S |  9 +++++++++
>>   arch/arm64/kernel/vdso32/vfutex.c   | 34 ++++++++++++++++++++++++++++++++++
>>   4 files changed, 61 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
>> index dc6b582736d0..5cae9c17ec72 100644
>> --- a/arch/arm64/kernel/vdso.c
>> +++ b/arch/arm64/kernel/vdso.c
>> @@ -78,11 +78,19 @@ static inline void vdso_futex_update_ips(struct mm_struct *mm)
>>   				VDSO_SYMBOL(vdso, futex_list64_try_unlock_cs_end));
>>   }
>>   
>> +static inline void aarch32_vdso_futex_update_ips(struct mm_struct *mm)
>> +{
>> +	unsigned long vdso = (unsigned long) mm->context.vdso;
>> +
>> +	__vdso_futex_update_ips(mm, true,
>> +				VDSO_SYMBOL(vdso, futex_list32_try_unlock_cs_start),
>> +				VDSO_SYMBOL(vdso, futex_list32_try_unlock_cs_end));
>> +}
>>   #else
>>   static inline void vdso_futex_update_ips(struct mm_struct *mm) {}
>> +static inline void aarch32_vdso_futex_update_ips(struct mm_struct *mm) {}
>>   #endif /* CONFIG_FUTEX_ROBUST_UNLOCK */
>>   
>> -
>>   static int vdso_mremap(const struct vm_special_mapping *sm,
>>   		struct vm_area_struct *new_vma)
>>   {
>> @@ -195,6 +203,8 @@ static int aarch32_mremap(const struct vm_special_mapping *sm,
>>   {
>>   	current->mm->context.vdso = (void *)new_vma->vm_start;
>>   
>> +	aarch32_vdso_futex_update_ips(current->mm);
>> +
>>   	return 0;
>>   }
>>   
>> @@ -327,6 +337,7 @@ static int aarch32_sigreturn_setup(struct mm_struct *mm)
>>   	return PTR_ERR_OR_ZERO(ret);
>>   }
>>   
>> +
>>   int aarch32_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
>>   {
>>   	struct mm_struct *mm = current->mm;
>> @@ -347,6 +358,8 @@ int aarch32_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
>>   	}
>>   
>>   	ret = aarch32_sigreturn_setup(mm);
>> +
>> +	aarch32_vdso_futex_update_ips(mm);
>>   out:
>>   	mmap_write_unlock(mm);
>>   	return ret;
>> diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile
>> index 4bd60f059f4a..f3190125c68b 100644
>> --- a/arch/arm64/kernel/vdso32/Makefile
>> +++ b/arch/arm64/kernel/vdso32/Makefile
>> @@ -97,6 +97,10 @@ munge := ../../../arm/vdso/vdsomunge
>>   hostprogs := $(munge)
>>   
>>   c-obj-vdso := note.o
>> +ifdef CONFIG_FUTEX_ROBUST_UNLOCK
>> +  c-obj-vdso += vfutex.o
>> +endif
>> +
>>   c-obj-vdso-gettimeofday := vgettimeofday.o
>>   
>>   ifneq ($(c-gettimeofday-y),)
>> diff --git a/arch/arm64/kernel/vdso32/vdso.lds.S b/arch/arm64/kernel/vdso32/vdso.lds.S
>> index 12bfc39e8aab..52ced27d6045 100644
>> --- a/arch/arm64/kernel/vdso32/vdso.lds.S
>> +++ b/arch/arm64/kernel/vdso32/vdso.lds.S
>> @@ -89,6 +89,15 @@ VERSION
>>   #endif /* CONFIG_COMPAT_32BIT_TIME */
>>   		__vdso_clock_gettime64;
>>   		__vdso_clock_getres_time64;
>> +#ifdef CONFIG_FUTEX_ROBUST_UNLOCK
>> +		__vdso_futex_robust_list32_try_unlock;
>> +#endif
>>   	local: *;
>>   	};
>>   }
>> +
>> +#ifdef CONFIG_FUTEX_ROBUST_UNLOCK
>> +VDSO_futex_list32_try_unlock_cs_success = __futex_list32_try_unlock_cs_success;
>> +VDSO_futex_list32_try_unlock_cs_start = __futex_list32_try_unlock_cs_start;
>> +VDSO_futex_list32_try_unlock_cs_end = __futex_list32_try_unlock_cs_end;
>> +#endif
>> diff --git a/arch/arm64/kernel/vdso32/vfutex.c b/arch/arm64/kernel/vdso32/vfutex.c
>> new file mode 100644
>> index 000000000000..0d9080b17965
>> --- /dev/null
>> +++ b/arch/arm64/kernel/vdso32/vfutex.c
>> @@ -0,0 +1,34 @@
>> +// SPDX-License-Identifier: GPL-2.0-or-later
>> +#include <linux/stringify.h>
>> +#include <vdso/futex.h>
>> +
>> +__u32 __vdso_futex_robust_list32_try_unlock(__u32 *lock, __u32 tid, __u32 *pop)
>> +{
>> +	register __u32 *pop_reg asm("r2") = pop, result_reg asm("r3") = 0;
>> +	__u32 val, zero = 0;
>> +
>> +	asm volatile (
>> +		".globl						  "
>> +		"__futex_list32_try_unlock_cs_start,		  "
>> +		"__futex_list32_try_unlock_cs_success,		  "
>> +		"__futex_list32_try_unlock_cs_end		\n"
>> +
>> +		"retry:						\n"
>> +		"	ldrex %[val], %[lock]			\n"
>> +		"	cmp %[tid], %[val]			\n"
>> +		"	bne __futex_list32_try_unlock_cs_end	\n"
>> +		"	stlex %[result], %[zero], %[lock]	\n"
>> +		"__futex_list32_try_unlock_cs_start:		\n"
>> +		"	cmp %[result], #0			\n"
>> +		"	bne retry				\n"
>> +		"__futex_list32_try_unlock_cs_success:		\n"
>> +		"	str %[zero], %[pop_reg]			\n"
>> +		"__futex_list32_try_unlock_cs_end:		\n"
>> +
>> +		: [val] "=&r" (val), [result] "=&r" (result_reg), [pop_reg] "+Q" (*pop_reg)
>> +		: [tid] "r" (tid), [lock] "Q" (*lock), [zero] "r" (zero)
>> +		: "cc", "memory"
>> +	);
>> +
>> +	return val;
>> +}
>>
>> -- 
>> 2.55.0
>>