Re: [PATCH v6 4/4] arm64: vdso32: Implement __vdso_futex_robust_try_unlock()

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

Em 20/07/2026 13:03, André Almeida escreveu:
> 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.
> 
> Signed-off-by: André Almeida <andrealmeid@igalia.com>

[...]

> +__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"
> +		"	strex %[result], %[zero], %[lock]	\n"

Actually, this should be `stlex` instead for the store release semantics.

> +		"__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)
> +		: [tid] "r" (tid), [lock] "Q" (*lock), [pop_reg] "Q" (*pop_reg), [zero] "r" (zero)
> +		: "cc", "memory"
> +	);
> +
> +	return val;
> +}
>