[DTrace-devel] [PATCH] cg, bpf: Pass dctx as first arg in arg-to-tstring subroutines

[Eugene Loh]

Reviewed-by: Eugene Loh <eugene.loh at oracle.com>
looks fine, though might be better as part of a patch series that uses it

On 7/21/23 14:00, Kris Van Hees via DTrace-devel wrote:
> Passing a pointer to the DTrace context (dctx) enables subroutines
> called through arg-to-tstring to report faults if necessary.  It also
> gives the implementation of these subroutines access to context data.
> (None use that as of yet, but e.g. inet_ntoa6() is expected to need
> it.)
>
> Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
> ---
>   bpf/basename.S    | 6 +++---
>   bpf/dirname.S     | 6 +++---
>   bpf/inet_ntoa.S   | 6 +++---
>   bpf/lltostr.S     | 6 +++---
>   libdtrace/dt_cg.c | 8 +++++---
>   5 files changed, 17 insertions(+), 15 deletions(-)
>
> diff --git a/bpf/basename.S b/bpf/basename.S
> index 23cf15d0..822e0517 100644
> --- a/bpf/basename.S
> +++ b/bpf/basename.S
> @@ -6,7 +6,7 @@
>   #define BPF_FUNC_probe_read_str	45
>   
>   /*
> - * void dt_basename(char *src, char *dst);
> + * void dt_basename(const dt_dctx_t *dctx, char *src, char *dst);
>    */
>   	.text
>   	.align	4
> @@ -19,8 +19,8 @@ dt_basename :
>   #define LEN %r9
>   
>   	/* store copies of input arguments */
> -	mov	SRC, %r1
> -	mov	DST, %r2
> +	mov	SRC, %r2
> +	mov	DST, %r3
>   
>   	/*
>   	 * Copy src to dst for two reasons:
> diff --git a/bpf/dirname.S b/bpf/dirname.S
> index 7ff90b47..2b902172 100644
> --- a/bpf/dirname.S
> +++ b/bpf/dirname.S
> @@ -6,7 +6,7 @@
>   #define BPF_FUNC_probe_read_str	45
>   
>   /*
> - * void dt_dirname(char *src, char *dst);
> + * void dt_dirname(const dt_dctx_t *dctx, char *src, char *dst);
>    */
>   	.text
>   	.align	4
> @@ -18,8 +18,8 @@ dt_dirname :
>   #define LEN %r8
>   
>   	/* store copies of input arguments */
> -	mov	SRC, %r1
> -	mov	DST, %r2
> +	mov	SRC, %r2
> +	mov	DST, %r3
>   
>   	/*
>   	 * Copy src to dst for two reasons:
> diff --git a/bpf/inet_ntoa.S b/bpf/inet_ntoa.S
> index 08b63b8d..24de04fd 100644
> --- a/bpf/inet_ntoa.S
> +++ b/bpf/inet_ntoa.S
> @@ -114,7 +114,7 @@ dt_inet_ntoa_write_uint8:
>   #undef PTR
>   
>   /*
> - * uint64_t dt_inet_ntoa(uint8_t *src, char *dst) {
> + * uint64_t dt_inet_ntoa(const dt_dctx_t *dctx, uint8_t *src, char *dst) {
>    *     uint64_t off, inp, len;
>    *
>    *     bpf_probe_read(fp + -4, 4, src);
> @@ -161,9 +161,9 @@ dt_inet_ntoa:
>   #define DST %r7
>   #define LEN %r8
>   
> -	mov	DST, %r2
> +	mov	DST, %r3
>   
> -	mov	%r3, %r1
> +	mov	%r3, %r2
>   	mov	%r2, 4
>   	mov	%r1, %fp
>   	add	%r1, -4
> diff --git a/bpf/lltostr.S b/bpf/lltostr.S
> index b21001ab..3fa2895c 100644
> --- a/bpf/lltostr.S
> +++ b/bpf/lltostr.S
> @@ -8,7 +8,7 @@
>   
>   	.text
>   /*
> - * void dt_lltostr(uint64_t VAL, char *STR)
> + * void dt_lltostr(const dt_dctx_t *dctx, uint64_t VAL, char *STR)
>    * {
>    *     // start writing at the end (IDX==1 is the last char)
>    *     IDX = 1
> @@ -74,8 +74,8 @@ dt_lltostr:
>   #define IDX %r8
>   #define SGN %r9
>   
> -	mov	VAL, %r1
> -	mov	STR, %r2
> +	mov	VAL, %r2
> +	mov	STR, %r3
>   
>   	mov	IDX, 1				/* IDX = 1 */
>   
> diff --git a/libdtrace/dt_cg.c b/libdtrace/dt_cg.c
> index 5391a143..bb6cff4a 100644
> --- a/libdtrace/dt_cg.c
> +++ b/libdtrace/dt_cg.c
> @@ -4567,7 +4567,8 @@ dt_cg_array_op(dt_node_t *dnp, dt_irlist_t *dlp, dt_regset_t *drp)
>   
>   /*
>    * Emit code to call a precompiled BPF function (named by fname)
> - * that is of return type void and takes two arguments:
> + * that is of return type void and takes three arguments:
> + *   - a pointer to the DTrace context (dctx)
>    *   - one input value
>    *   - a pointer to an output tstring, allocated here
>    */
> @@ -4599,12 +4600,13 @@ dt_cg_subr_arg_to_tstring(dt_node_t *dnp, dt_irlist_t *dlp, dt_regset_t *drp,
>   	if (dt_regset_xalloc_args(drp) == -1)
>   		longjmp(yypcb->pcb_jmpbuf, EDT_NOREG);
>   
> -	emit(dlp, BPF_MOV_REG(BPF_REG_1, arg->dn_reg));
> +	emit(dlp, BPF_LOAD(BPF_DW, BPF_REG_1, BPF_REG_FP, DT_STK_DCTX));
> +	emit(dlp, BPF_MOV_REG(BPF_REG_2, arg->dn_reg));
>   	dt_regset_free(drp, arg->dn_reg);
>   	if (dt_node_is_string(arg))
>   		dt_cg_tstring_free(yypcb, arg);
>   
> -	emit(dlp,  BPF_MOV_REG(BPF_REG_2, dnp->dn_reg));
> +	emit(dlp,  BPF_MOV_REG(BPF_REG_3, dnp->dn_reg));
>   
>   	idp = dt_dlib_get_func(yypcb->pcb_hdl, fname);
>   	assert(idp != NULL);