[DTrace-devel] [PATCH v3 1/7] cg: move get_member() to dt_cg.c
Kris Van Hees
kris.van.hees at oracle.com
Mon Jul 21 20:37:47 UTC 2025
On Wed, Jul 09, 2025 at 03:09:42PM +0100, Alan Maguire via DTrace-devel wrote:
> It will be used by both dt_prov_ip.c and dt_prov_tcp.c.
>
> Signed-off-by: Alan Maguire <alan.maguire at oracle.com>
> Reviewed-by: Eugene Loh <eugene.loh at oracle.com>
Reviewed-by: Kris Van Hees <kris.van.hees at oracle.com>
... albeit a newer version that is a collaboration of Alan and I to improve
(what is now called) dt_cg_tramp_get_member()
> ---
> libdtrace/dt_cg.c | 39 ++++++++++++++++++++++++++++++++++++
> libdtrace/dt_cg.h | 2 ++
> libdtrace/dt_prov_ip.c | 45 ++++--------------------------------------
> 3 files changed, 45 insertions(+), 41 deletions(-)
>
> diff --git a/libdtrace/dt_cg.c b/libdtrace/dt_cg.c
> index bd0763d6..d6fc8259 100644
> --- a/libdtrace/dt_cg.c
> +++ b/libdtrace/dt_cg.c
> @@ -1901,6 +1901,45 @@ dt_cg_ctf_offsetof(const char *structname, const char *membername,
> return (ctm.ctm_offset / NBBY);
> }
>
> +/*
> + * Retrieve the value of a member in a given struct.
> + *
> + * Entry:
> + * reg = TYPE *ptr
> + *
> + * Return:
> + * %r0 = ptr->member
> + * Clobbers:
> + * %r1 .. %r5
> + */
> +int
> +dt_cg_get_member(dt_pcb_t *pcb, const char *name, int reg,
> + const char *member)
> +{
> + dtrace_hdl_t *dtp = pcb->pcb_hdl;
> + dt_irlist_t *dlp = &pcb->pcb_ir;
> + dtrace_typeinfo_t tt;
> + ctf_membinfo_t ctm;
> + size_t size;
> + uint_t ldop;
> +
> + if (dtrace_lookup_by_type(dtp, DTRACE_OBJ_KMODS, name, &tt) == -1 ||
> + ctf_member_info(tt.dtt_ctfp, tt.dtt_type, member, &ctm) == CTF_ERR)
> + return -1;
> +
> + ldop = dt_cg_ldsize(NULL, tt.dtt_ctfp, ctm.ctm_type, &size);
> +
> + emit(dlp, BPF_MOV_REG(BPF_REG_3, reg));
> + emit(dlp, BPF_ALU64_IMM(BPF_ADD, BPF_REG_3, ctm.ctm_offset / NBBY));
> + emit(dlp, BPF_MOV_IMM(BPF_REG_2, size));
> + emit(dlp, BPF_MOV_REG(BPF_REG_1, BPF_REG_FP));
> + emit(dlp, BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, DT_TRAMP_SP_BASE));
> + emit(dlp, BPF_CALL_HELPER(dtp->dt_bpfhelper[BPF_FUNC_probe_read_kernel]));
> + emit(dlp, BPF_LOAD(ldop, BPF_REG_0, BPF_REG_FP, DT_TRAMP_SP_BASE));
> +
> + return 0;
> +}
> +
> static void
> dt_cg_act_breakpoint(dt_pcb_t *pcb, dt_node_t *dnp, dtrace_actkind_t kind)
> {
> diff --git a/libdtrace/dt_cg.h b/libdtrace/dt_cg.h
> index 81b79399..36f587d3 100644
> --- a/libdtrace/dt_cg.h
> +++ b/libdtrace/dt_cg.h
> @@ -44,6 +44,8 @@ extern void dt_cg_tramp_epilogue_advance(dt_pcb_t *pcb, dt_activity_t act);
> extern void dt_cg_tramp_error(dt_pcb_t *pcb);
> extern int dt_cg_ctf_offsetof(const char *structname, const char *membername,
> size_t *sizep, int relaxed);
> +extern int dt_cg_get_member(dt_pcb_t *pcb, const char *name, int reg,
> + const char *member);
> extern uint_t dt_cg_ldsize(dt_node_t *dnp, ctf_file_t *ctfp, ctf_id_t type,
> ssize_t *ret_size);
> extern uint_t bpf_ldst_size(ssize_t size, int store);
> diff --git a/libdtrace/dt_prov_ip.c b/libdtrace/dt_prov_ip.c
> index c4a3a6e2..37f91e3d 100644
> --- a/libdtrace/dt_prov_ip.c
> +++ b/libdtrace/dt_prov_ip.c
> @@ -62,43 +62,6 @@ static int populate(dtrace_hdl_t *dtp)
> probe_args, probes);
> }
>
> -/*
> - * Retrieve the value of a member in a given struct.
> - *
> - * Entry:
> - * reg = TYPE *ptr
> - *
> - * Return:
> - * %r0 = ptr->member
> - * Clobbers:
> - * %r1 .. %r5
> - */
> -static int get_member(dt_pcb_t *pcb, const char *name, int reg,
> - const char *member) {
> - dtrace_hdl_t *dtp = pcb->pcb_hdl;
> - dt_irlist_t *dlp = &pcb->pcb_ir;
> - dtrace_typeinfo_t tt;
> - ctf_membinfo_t ctm;
> - size_t size;
> - uint_t ldop;
> -
> - if (dtrace_lookup_by_type(dtp, DTRACE_OBJ_KMODS, name, &tt) == -1 ||
> - ctf_member_info(tt.dtt_ctfp, tt.dtt_type, member, &ctm) == CTF_ERR)
> - return -1;
> -
> - ldop = dt_cg_ldsize(NULL, tt.dtt_ctfp, ctm.ctm_type, &size);
> -
> - emit(dlp, BPF_MOV_REG(BPF_REG_3, reg));
> - emit(dlp, BPF_ALU64_IMM(BPF_ADD, BPF_REG_3, ctm.ctm_offset / NBBY));
> - emit(dlp, BPF_MOV_IMM(BPF_REG_2, size));
> - emit(dlp, BPF_MOV_REG(BPF_REG_1, BPF_REG_FP));
> - emit(dlp, BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, DT_TRAMP_SP_BASE));
> - emit(dlp, BPF_CALL_HELPER(dtp->dt_bpfhelper[BPF_FUNC_probe_read_kernel]));
> - emit(dlp, BPF_LOAD(ldop, BPF_REG_0, BPF_REG_FP, DT_TRAMP_SP_BASE));
> -
> - return 0;
> -}
> -
> /*
> * Generate a BPF trampoline for a SDT probe.
> *
> @@ -142,7 +105,7 @@ static int trampoline(dt_pcb_t *pcb, uint_t exitlbl)
>
> emit(dlp, BPF_STORE(BPF_DW, BPF_REG_7, DMST_ARG(0), BPF_REG_6));
>
> - get_member(pcb, "struct sk_buff", BPF_REG_6, "sk");
> + dt_cg_get_member(pcb, "struct sk_buff", BPF_REG_6, "sk");
> emit(dlp, BPF_STORE(BPF_DW, BPF_REG_7, DMST_ARG(1), BPF_REG_0));
>
> /*
> @@ -150,11 +113,11 @@ static int trampoline(dt_pcb_t *pcb, uint_t exitlbl)
> * skb_network_header(skb) = (include/linux/ip.h)
> * skb->head + skb->network_header (include/linux/skbuff.h)
> */
> - get_member(pcb, "struct sk_buff", BPF_REG_6, "head");
> + dt_cg_get_member(pcb, "struct sk_buff", BPF_REG_6, "head");
> emit(dlp, BPF_STORE(BPF_DW, BPF_REG_7, DMST_ARG(2), BPF_REG_0));
> emit(dlp, BPF_STORE(BPF_DW, BPF_REG_7, DMST_ARG(4), BPF_REG_0));
> emit(dlp, BPF_STORE(BPF_DW, BPF_REG_7, DMST_ARG(5), BPF_REG_0));
> - get_member(pcb, "struct sk_buff", BPF_REG_6, "network_header");
> + dt_cg_get_member(pcb, "struct sk_buff", BPF_REG_6, "network_header");
> emit(dlp, BPF_XADD_REG(BPF_DW, BPF_REG_7, DMST_ARG(2), BPF_REG_0));
> emit(dlp, BPF_XADD_REG(BPF_DW, BPF_REG_7, DMST_ARG(4), BPF_REG_0));
> emit(dlp, BPF_XADD_REG(BPF_DW, BPF_REG_7, DMST_ARG(5), BPF_REG_0));
> @@ -168,7 +131,7 @@ static int trampoline(dt_pcb_t *pcb, uint_t exitlbl)
> else
> emit(dlp, BPF_STORE_IMM(BPF_DW, BPF_REG_7, DMST_ARG(5), 0));
>
> - get_member(pcb, "struct sk_buff", BPF_REG_6, "dev");
> + dt_cg_get_member(pcb, "struct sk_buff", BPF_REG_6, "dev");
> emit(dlp, BPF_STORE(BPF_DW, BPF_REG_7, DMST_ARG(3), BPF_REG_0));
>
> return 0;
> --
> 2.39.3
>
>
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