[PATCH v2] arm: fix memset-related crashes caused by recent GCC (4.7.2) optimizations

[Dirk Behme]

Am 11.02.2013 13:57, schrieb Ivan Djelic:
> Recent GCC versions (e.g. GCC-4.7.2) perform optimizations based on
> assumptions about the implementation of memset and similar functions.
> The current ARM optimized memset code does not return the value of
> its first argument, as is usually expected from standard implementations.
>
> For instance in the following function:
>
> void debug_mutex_lock_common(struct mutex *lock, struct mutex_waiter *waiter)
> {
> 	memset(waiter, MUTEX_DEBUG_INIT, sizeof(*waiter));
> 	waiter->magic = waiter;
> 	INIT_LIST_HEAD(&waiter->list);
> }
>
> compiled as:
>
> 800554d0 <debug_mutex_lock_common>:
> 800554d0:       e92d4008        push    {r3, lr}
> 800554d4:       e1a00001        mov     r0, r1
> 800554d8:       e3a02010        mov     r2, #16 ; 0x10
> 800554dc:       e3a01011        mov     r1, #17 ; 0x11
> 800554e0:       eb04426e        bl      80165ea0 <memset>
> 800554e4:       e1a03000        mov     r3, r0
> 800554e8:       e583000c        str     r0, [r3, #12]
> 800554ec:       e5830000        str     r0, [r3]
> 800554f0:       e5830004        str     r0, [r3, #4]
> 800554f4:       e8bd8008        pop     {r3, pc}
>
> GCC assumes memset returns the value of pointer 'waiter' in register r0; causing
> register/memory corruptions.
>
> This patch fixes the return value of the assembly version of memset.
> It adds a 'mov' instruction and merges an additional load+store into
> existing load/store instructions.
> For ease of review, here is a breakdown of the patch into 4 simple steps:
>
> Step 1
> ======
> Perform the following substitutions:
> ip -> r8, then
> r0 -> ip,
> and insert 'mov ip, r0' as the first statement of the function.
> At this point, we have a memset() implementation returning the proper result,
> but corrupting r8 on some paths (the ones that were using ip).
>
> Step 2
> ======
> Make sure r8 is saved and restored when (! CALGN(1)+0) == 1:
>
> save r8:
> -       str     lr, [sp, #-4]!
> +       stmfd   sp!, {r8, lr}
>
> and restore r8 on both exit paths:
> -       ldmeqfd sp!, {pc}               @ Now <64 bytes to go.
> +       ldmeqfd sp!, {r8, pc}           @ Now <64 bytes to go.
> (...)
>          tst     r2, #16
>          stmneia ip!, {r1, r3, r8, lr}
> -       ldr     lr, [sp], #4
> +       ldmfd   sp!, {r8, lr}
>
> Step 3
> ======
> Make sure r8 is saved and restored when (! CALGN(1)+0) == 0:
>
> save r8:
> -       stmfd   sp!, {r4-r7, lr}
> +       stmfd   sp!, {r4-r8, lr}
>
> and restore r8 on both exit paths:
>          bgt     3b
> -       ldmeqfd sp!, {r4-r7, pc}
> +       ldmeqfd sp!, {r4-r8, pc}
> (...)
>          tst     r2, #16
>          stmneia ip!, {r4-r7}
> -       ldmfd   sp!, {r4-r7, lr}
> +       ldmfd   sp!, {r4-r8, lr}
>
> Step 4
> ======
> Rewrite register list "r4-r7, r8" as "r4-r8".
>
> Signed-off-by: Ivan Djelic <ivan.djelic at parrot.com>
> Reviewed-by: Nicolas Pitre <nico at linaro.org>

Sent as 7668/1 to rmk's patch system.

Thanks

Dirk