Re: [PATCH] selftests/powerpc: Fix ptrace tm failure

[Segher Boessenkool <segher@kernel.crashing.org>]

On Mon, Oct 22, 2018 at 06:16:26PM -0300, Breno Leitao wrote:
> Test ptrace-tm-spd-gpr fails on current kernel (4.19) due to a segmentation
> fault that happens on the child process prior to setting cptr[2] = 1. This
> causes the parent process to wait forever at 'while (!pptr[2])' and the test to
> be killed by the test harness framework by timeout, thus, failing.
> 
> The segmentation fault happens because of a inline assembly being
> generated as:
> 
> 	0x10000355c <tm_spd_gpr+492>    lfs    f0, 0(0)
> 
> This is reading memory position 0x0 and causing the segmentation fault.
> 
> This code is being generated by ASM_LOAD_FPR_SINGLE_PRECISION(flt_4), where
> flt_4 is passed to the inline assembly block as:
> 
> 	[flt_4] "r" (&d)
> 
> Since the inline assembly 'r' constraint means any GPR, gpr0 is being
> chosen, thus causing this issue when issuing a Load Floating-Point Single
> instruction.
> 
> This patch simply changes the constraint to 'b', which specify that this
> register will be used as base, and r0 is not allowed to be used, avoiding
> this issue.
> 
> Other than that, removing flt_2 register from the input operands, since it
> is not used by the inline assembly code at all.
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: Breno Leitao <leitao@debian.org>

Acked-by: Segher Boessenkool <segher@kernel.crashing.org>


Segher