Re: [PATCH] Aarch64 SVE: Fix stack smashing when calling functions

[Joel Brobecker <brobecker@adacore.com>]

Hi Alan,

> Using "call" on a function that passes arguments via float registers can cause
> gdb to overflow buffers.

> Ensure enough memory is reserved to hold a full FP register.
> 
> 2018-09-17  Alan Hayward  <alan.hayward@arm.com>
> 
> 	* aarch64-tdep.c (pass_in_v): Use register size.
> 	(aarch64_extract_return_value): Likewise.
> 	(aarch64_store_return_value): Likewise.

Do we have a testcase already that demonstrates the problem?
Otherwise, it would be nice to add one.

> diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
> index 6993e9061e..516eb138dc 100644
> --- a/gdb/aarch64-tdep.c
> +++ b/gdb/aarch64-tdep.c
> @@ -1358,7 +1358,10 @@ pass_in_v (struct gdbarch *gdbarch,
>    if (info->nsrn < 8)
>      {
>        int regnum = AARCH64_V0_REGNUM + info->nsrn;
> -      gdb_byte reg[V_REGISTER_SIZE];
> +      /* Enough space for a full vector register.  */
> +      gdb_byte reg[register_size (gdbarch, regnum)];
> +      gdb_static_assert (AARCH64_V0_REGNUM == AARCH64_SVE_Z0_REGNUM);
> +      gdb_assert (len <= sizeof (reg));

Could you explain the relationship between making the buffer large
enough, which is the purpose of this patch, and the assertion that
AARCH64_V0_REGNUM == AARCH64_SVE_Z0_REGNUM?

I don't see a problem with that assertion, but for archeology
purposes, it is better to decorelate changes that are independent.
It helps better document why we introduced changes.

>  
>        info->argnum++;
>        info->nsrn++;
> @@ -1929,7 +1932,10 @@ aarch64_extract_return_value (struct type *type, struct regcache *regs,
>        for (int i = 0; i < elements; i++)
>  	{
>  	  int regno = AARCH64_V0_REGNUM + i;
> -	  bfd_byte buf[V_REGISTER_SIZE];
> +	  /* Enough space for a full vector register.  */
> +	  gdb_byte buf[register_size (gdbarch, regno)];
> +	  gdb_static_assert (AARCH64_V0_REGNUM == AARCH64_SVE_Z0_REGNUM);
> +	  gdb_assert (len <= sizeof (buf));
>  
>  	  if (aarch64_debug)
>  	    {
> @@ -2039,7 +2045,10 @@ aarch64_store_return_value (struct type *type, struct regcache *regs,
>        for (int i = 0; i < elements; i++)
>  	{
>  	  int regno = AARCH64_V0_REGNUM + i;
> -	  bfd_byte tmpbuf[V_REGISTER_SIZE];
> +	  /* Enough space for a full vector register.  */
> +	  gdb_byte tmpbuf[register_size (gdbarch, regno)];
> +	  gdb_static_assert (AARCH64_V0_REGNUM == AARCH64_SVE_Z0_REGNUM);
> +	  gdb_assert (len <= sizeof (tmpbuf));
>  
>  	  if (aarch64_debug)
>  	    {
> -- 
> 2.15.2 (Apple Git-101.1)

Thank you!

-- 
Joel