[DTrace-devel] [PATCH v2] Minor edits

[Kris Van Hees]

On Mon, Feb 28, 2022 at 05:16:44PM -0500, eugene.loh--- via DTrace-devel wrote:
> From: Eugene Loh <eugene.loh at oracle.com>
> 
> Jump to Lempty for zero-length source strings.  Remove dead code
> claiming to reuse register for dnp->dn_reg.
> 
> Signed-off-by: Eugene Loh <eugene.loh at oracle.com>

Reviewed-by: Kris Van Hees <kris.van.hees at oracle.com>

... and I am putting it on dev.

> ---
>  bpf/substr.S      | 8 ++++----
>  libdtrace/dt_cg.c | 1 -
>  2 files changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/bpf/substr.S b/bpf/substr.S
> index 8d501faa..886a7200 100644
> --- a/bpf/substr.S
> +++ b/bpf/substr.S
> @@ -41,9 +41,9 @@ dt_substr :
>  
>  	/*
>  	 * Get the source string length and validate it.
> -	 * If the return value of probe_read_str) is less than 0, an error
> -	 * occured, and the result will be the empty string.
> -	 * If the length is 0, the result is the empty string.
> +	 * If the return value of probe_read_str() is less than 0, an error
> +	 * occurred, and the result will be the empty string.
> +	 * If the length is 1, the result is the empty string.
>  	 * If the length is less than the maximum string length (STRSZ), use
>  	 * the length we got.  (The length is initialized in %r8 as the default
>  	 * string length.)
> @@ -55,7 +55,7 @@ dt_substr :
>  					 * len = probe_read_str(dst, STRSZ + 1,
>  					 *			src);
>  					 */
> -	jslt	%r0, 1, .Lempty		/* if (len < 1) goto Lempty; */
> +	jsle	%r0, 1, .Lempty		/* if (len <= 1) goto Lempty; */
>  	sub	%r0, 1			/* len--; */
>  	mov	%r4, %r8		/* %r4 = STRSZ (previously in %r8) */
>  	mov	%r8, %r0		/* %r8 = len */
> diff --git a/libdtrace/dt_cg.c b/libdtrace/dt_cg.c
> index 59c4fdc5..d4a58667 100644
> --- a/libdtrace/dt_cg.c
> +++ b/libdtrace/dt_cg.c
> @@ -3989,7 +3989,6 @@ dt_cg_subr_strlen(dt_node_t *dnp, dt_irlist_t *dlp, dt_regset_t *drp)
>  
>  	dt_cg_node(str, dlp, drp);
>  	dt_cg_check_notnull(dlp, drp, str->dn_reg);
> -	dnp->dn_reg = str->dn_reg;		/* re-use register */
>  
>  	if (dt_regset_xalloc_args(drp) == -1)
>  		longjmp(yypcb->pcb_jmpbuf, EDT_NOREG);
> -- 
> 2.18.4
> 
> 
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