[DTrace-devel] [PATCH] Fix value of post-decrement expressions

[Kris Van Hees]

Please change the subject of your patch to not be identical to the commit
you are fixing.  It gets really confusing to get multiple patches with the
same name, especially when one is fixing an issue with an earlier one.

A good alternative wuold be:

Reverse order of operands in postarith expressions

or something like that (since that is in fact the fix).

Other than that, nice catch!

On Sat, Aug 22, 2020 at 01:46:22AM -0400, eugene.loh at oracle.com wrote:
> From: Eugene Loh <eugene.loh at oracle.com>
> 
> An earlier commit ("17b0da163 Fix value of post-increment expressions")
> purported to fix postfix expressions, but it formed (1 op arg) rather than
> (arg op 1), as is evident not only in the code but even in the commit
> message.  Arguably, the distinction is unimportant for increment, since
> addition is commutative, but the patch produced incorrect results for
> decrement expressions.
> 
> Fix the generated code and remove the XFAIL on the associated test.
> 
> Orabug: 31787365
> Signed-off-by: Eugene Loh <eugene.loh at oracle.com>
> ---
>  libdtrace/dt_cg.c                      | 4 ++--
>  test/unittest/arithmetic/tst.complex.d | 1 -
>  2 files changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/libdtrace/dt_cg.c b/libdtrace/dt_cg.c
> index f183d774..95a6c813 100644
> --- a/libdtrace/dt_cg.c
> +++ b/libdtrace/dt_cg.c
> @@ -1911,9 +1911,9 @@ dt_cg_postarith_op(dt_node_t *dnp, dt_irlist_t *dlp,
>  	if (nreg == -1)
>  		longjmp(yypcb->pcb_jmpbuf, EDT_NOREG);
>  
> -	instr = BPF_MOV_IMM(nreg, size);
> +	instr = BPF_MOV_REG(nreg, oreg);
>  	dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
> -	instr = BPF_ALU64_REG(op, nreg, dnp->dn_reg);
> +	instr = BPF_ALU64_IMM(op, nreg, size);
>  	dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
>  
>  	/*
> diff --git a/test/unittest/arithmetic/tst.complex.d b/test/unittest/arithmetic/tst.complex.d
> index 6a8a19a7..f9d7480b 100644
> --- a/test/unittest/arithmetic/tst.complex.d
> +++ b/test/unittest/arithmetic/tst.complex.d
> @@ -14,7 +14,6 @@
>   * SECTION: Types, Operators, and Expressions/Arithmetic Operators
>   *
>   */
> -/* @@xfail: dtv2 */
>  
>  #pragma D option quiet
>  
> -- 
> 2.18.4
> 
> 
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