ply: add dynamic tracing package using BPF

ply is a light-weight dynamic tracer for Linux that leverages the kernel's
BPF VM in concert with kprobes/tracepoints to attach probes to arbitrary
points in the kernel.

Most tracers that generate BPF bytecode are based on the LLVM-based BCC
toolchain; ply on the other hand has no external dependencies outside libc,
making it suitable for use on constrained embedded systems.

Currently ply supports x86_64, aarch64, arm, riscv64, riscv32, powerpc,
mips(el), and mips64(el) architectures.

Further documentation, examples and implementation details may be found at:
https://github.com/iovisor/ply.

Signed-off-by: Tony Ambardar <[email protected]>

package/devel/ply/Makefile

@@ -0,0 +1,54 @@
+#
+# Copyright (C) 2022 Ye Jiaqiang, Tony Ambardar
+#
+# This is free software, licensed under the GNU General Public License v2.
+# See /LICENSE for more information.
+#
+
+include $(TOPDIR)/rules.mk
+
+PKG_NAME:=ply
+PKG_RELEASE:=1
+
+PKG_SOURCE_PROTO:=git
+PKG_SOURCE_URL:=https://github.com/iovisor/ply.git
+PKG_MIRROR_HASH:=d4f434c4d11b662b61da2de8b5a29ecdeac655aa5158f4c4127e2a91047c0c54
+PKG_SOURCE_DATE:=2023-05-16
+PKG_SOURCE_VERSION:=1b57943db56692924bccb61c271de24a8264d8df
+
+PKG_LICENSE:=GPLv2
+PKG_LICENSE_FILES:=COPYING
+PKG_MAINTAINER:=Tony Ambardar <[email protected]>
+
+include $(INCLUDE_DIR)/package.mk
+
+define Package/ply
+  SECTION:=devel
+  CATEGORY:=Development
+  TITLE:=Light-weight dynamic tracer for Linux
+  URL:=https://github.com/iovisor/ply.git
+  DEPENDS:= \
+	@KERNEL_BPF_EVENTS @KERNEL_DYNAMIC_FTRACE @KERNEL_DEBUG_FS \
+	@mips||mipsel||mips64||mips64el||x86_64||powerpc||arm_v7||aarch64||riscv||riscv64
+endef
+
+define Package/ply/description
+  A light-weight dynamic tracer for Linux that leverages the kernel's
+  BPF VM in concert with kprobes and tracepoints to attach probes to
+  arbitrary points in the kernel.
+endef
+
+CONFIGURE_ARGS += --enable-shared=yes --enable-static=no
+
+define Build/Prepare
+	$(call Build/Prepare/Default)
+	cd $(PKG_BUILD_DIR) && exec ./autogen.sh
+endef
+
+define Package/ply/install
+	$(INSTALL_DIR) $(1)/usr/bin $(1)/usr/lib
+	$(INSTALL_BIN) $(PKG_BUILD_DIR)/src/ply/.libs/ply $(1)/usr/bin/
+	$(CP) $(PKG_BUILD_DIR)/src/libply/.libs/libply.so* $(1)/usr/lib/
+endef
+
+$(eval $(call BuildPackage,ply))

package/devel/ply/patches/100-revert-read-kernel-variants.patch

@@ -0,0 +1,94 @@
+From 755220eb974708615b14bcdc6412319698e0485d Mon Sep 17 00:00:00 2001
+From: Tony Ambardar <[email protected]>
+Date: Thu, 22 Dec 2022 22:53:10 -0800
+Subject: [PATCH] Revert "ply: Use new read_kernel variants"
+
+This reverts commit 17864b9818cceca09f31a346908afe1c718c10c5.
+
+Fixes: 17864b98 ("ply: Use new read_kernel variants")
+Signed-off-by: Tony Ambardar <[email protected]>
+---
+ src/libply/built-in/memory.c     | 10 +++++-----
+ src/libply/ir.c                  | 10 +++++-----
+ src/libply/provider/tracepoint.c |  2 +-
+ 3 files changed, 11 insertions(+), 11 deletions(-)
+
+--- a/src/libply/built-in/memory.c
++++ b/src/libply/built-in/memory.c
+@@ -140,7 +140,7 @@ static int str_ir_post(const struct func
+ 	ir_emit_ldbp(pb->ir, BPF_REG_1, n->sym->irs.stack);
+ 	ir_emit_insn(ir, MOV_IMM((int32_t)type_sizeof(n->sym->type)), BPF_REG_2, 0);
+ 	ir_emit_sym_to_reg(ir, BPF_REG_3, ptr->sym);
+-	ir_emit_insn(ir, CALL(BPF_FUNC_probe_read_kernel_str), 0, 0);
++	ir_emit_insn(ir, CALL(BPF_FUNC_probe_read_str), 0, 0);
+ 	return 0;
+ }
+
+@@ -305,7 +305,7 @@ static int struct_dot_ir_pre(const struc
+ 		sou->sym->irs.hint.dot = 1;
+
+ 		/* this also means we need to put ourselves on the
+-		 * stack since data will be loaded via probe_read_kernel */
++		 * stack since data will be loaded via probe_read */
+ 		n->sym->irs.hint.stack = 1;
+ 	}
+ 	return 0;
+@@ -334,7 +334,7 @@ static int struct_dot_ir_post(const stru
+
+ 		ir_emit_sym_to_reg(pb->ir, BPF_REG_3, ptr->sym);
+ 		ir_emit_insn(pb->ir, ALU64_IMM(BPF_ADD, offset), BPF_REG_3, 0);
+-		goto probe_read_kernel;
++		goto probe_read;
+ 	}
+
+ 	offset += sou->sym->irs.stack;
+@@ -346,10 +346,10 @@ static int struct_dot_ir_post(const stru
+ 	}
+
+ 	ir_emit_insn(pb->ir, ALU_IMM(BPF_ADD, offset), BPF_REG_3, 0);
+-probe_read_kernel:
++probe_read:
+ 	ir_emit_insn(pb->ir, MOV_IMM((int32_t)dst->size), BPF_REG_2, 0);
+ 	ir_emit_ldbp(pb->ir, BPF_REG_1, dst->stack);
+-	ir_emit_insn(pb->ir, CALL(BPF_FUNC_probe_read_kernel), 0, 0);
++	ir_emit_insn(pb->ir, CALL(BPF_FUNC_probe_read), 0, 0);
+ 	/* TODO if (r0) exit(r0); */
+ 	return 0;
+ }
+--- a/src/libply/ir.c
++++ b/src/libply/ir.c
+@@ -38,10 +38,10 @@ static const char *bpf_func_name(enum bp
+ 		return "map_update_elem";
+ 	case BPF_FUNC_perf_event_output:
+ 		return "perf_event_output";
+-	case BPF_FUNC_probe_read_kernel:
+-		return "probe_read_kernel";
+-	case BPF_FUNC_probe_read_kernel_str:
+-		return "probe_read_kernel_str";
++	case BPF_FUNC_probe_read:
++		return "probe_read";
++	case BPF_FUNC_probe_read_str:
++		return "probe_read_str";
+ 	case BPF_FUNC_trace_printk:
+ 		return "trace_printk";
+ 	default:
+@@ -416,7 +416,7 @@ void ir_emit_read_to_sym(struct ir *ir,
+ 	if (src != BPF_REG_3)
+ 		ir_emit_insn(ir, MOV, BPF_REG_3, src);
+
+-	ir_emit_insn(ir, CALL(BPF_FUNC_probe_read_kernel), 0, 0);
++	ir_emit_insn(ir, CALL(BPF_FUNC_probe_read), 0, 0);
+ 	/* TODO if (r0) exit(r0); */
+ }
+
+--- a/src/libply/provider/tracepoint.c
++++ b/src/libply/provider/tracepoint.c
+@@ -68,7 +68,7 @@ static int tracepoint_dyn_ir_post(const
+ 	ir_emit_insn(ir, ALU_IMM(BPF_AND, 0xffff), BPF_REG_4, 0);
+ 	ir_emit_insn(ir, ALU64(BPF_ADD), BPF_REG_3, BPF_REG_4);
+
+-	ir_emit_insn(ir, CALL(BPF_FUNC_probe_read_kernel), 0, 0);
++	ir_emit_insn(ir, CALL(BPF_FUNC_probe_read), 0, 0);
+ 	return 0;
+ }
+