Add USDT header file to folly

Summary:
Derived from `sdt.h` in [[ https://sourceware.org/systemtap/ | SystemTap ]]
Performed changes and clean-ups including:
- Get rid of the `sdt-config.h`.
- Get rid of "Running in Assembler" code.
- Replace the `DTRACE_PROBE_1, ... DTRACE_PROBE_N` Macro family with a single Macro using the "count Macro arguments" trick
- Get rid of argument signed-ness calculation. A **lot** of painful code were there only for this, and it has no real usage except for displaying purposes.
- Re-structure the helper methods (Macros) so that the logic of the code is a bit more readable.
- Add some comments so that it would be easier for users and future developers to understand what this header file is actually doing.
- Update license banner.

Reviewed By: meyering

Differential Revision: D3792966

fbshipit-source-id: 564a1011f7946d30be78191f334e072d94fa264e

folly/tracing/README.md

+# folly/tracing: Utility for User-level Statically Defined Tracing
+----------------------------------------------------------
+
+## StaticTracepoint
+
+The `StaticTracepoint.h` header file defines the Macro
+```
+FOLLY_SDT(provider, name, arg1, arg2, ...)
+```
+Invoking the Macro will add a Static Tracepoint at the calling location. Using a
+tracing toolkit ([BCC](https://github.com/iovisor/bcc) is an excellent example),
+a probe can be attached to the Tracepoint, consume the provided arguments and
+perform other tracing / profiling works.
+
+The Tracepoint defined using `StaticTracepoint.h` is also compatible with any
+toolkit designed for consuming [SystemTap](https://sourceware.org/systemtap/)
+Tracepoints.
+
+Internally, the Macro emits a `nop` operation at the calling location, along
+with an Assembler Instruction with empty template and empty output Operands,
+and the provided arguments and their sizes as input Operands.
+
+The Macro then append to the ELF `.note` section, with information including
+the provider and name of the Tracepoint, address of the `nop` operation, and
+size and location (register name or memory location) of the provided arguments.
+This way, the tracing toolkits would be able to parse the information, attach
+the probes to the correct address, and consume arguments.
+
+The default constraint for the arguments in the Assembler Instruction as
+operands is `"nor"`. It means the argument could be an immediate integer
+operand, a register operand or an offsettable memory operand. This is a good
+default since tracing arguments tend to be integral, and the number of arguments
+is likely to be less than the number of registers.
+
+Otherwise, you may see compiler report errors like
+```
+'asm' requires impossible reload
+```
+You may want to simplify the Tracepoint (fewer and simpler arguments) in
+such case. You may also choose to override the constraint
+```
+#define FOLLY_SDT_ARG_CONSTRAINT "g"
+```
+which means the arguments can be any memory or register operands.

folly/tracing/StaticTracepoint-ELFx86.h

+/*
+ * Copyright 2016 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+// Default constraint for the probe arguments as operands.
+#ifndef FOLLY_SDT_ARG_CONSTRAINT
+#define FOLLY_SDT_ARG_CONSTRAINT      "nor"
+#endif
+
+// Instruction to emit for the probe.
+#define FOLLY_SDT_NOP                 nop
+
+// Note section properties.
+#define FOLLY_SDT_NOTE_NAME           "stapsdt"
+#define FOLLY_SDT_NOTE_TYPE           3
+
+// Size of address depending on platform.
+#ifdef __LP64__
+#define FOLLY_SDT_ASM_ADDR            .8byte
+#else
+#define FOLLY_SDT_ASM_ADDR            .4byte
+#endif
+
+// Assembler helper Macros.
+#define FOLLY_SDT_S(x)                #x
+#define FOLLY_SDT_ASM_1(x)            FOLLY_SDT_S(x) "\n"
+#define FOLLY_SDT_ASM_2(a, b)         FOLLY_SDT_S(a) "," FOLLY_SDT_S(b) "\n"
+#define FOLLY_SDT_ASM_3(a, b, c)      FOLLY_SDT_S(a) "," FOLLY_SDT_S(b) ","    \
+                                      FOLLY_SDT_S(c) "\n"
+#define FOLLY_SDT_ASM_STRING(x)       FOLLY_SDT_ASM_1(.asciz FOLLY_SDT_S(x))
+
+// Helper to determine the size of an argument.
+#define FOLLY_SDT_ISARRAY(x)  (__builtin_classify_type(x) == 14)
+#define FOLLY_SDT_ARGSIZE(x)  (FOLLY_SDT_ISARRAY(x) ? sizeof(void*) : sizeof(x))
+
+// Format of each probe arguments as operand.
+// Size of the arugment tagged with FOLLY_SDT_Sn, with "n" constraint.
+// Value of the argument tagged with FOLLY_SDT_An, with configured constraint.
+#define FOLLY_SDT_ARG(n, x)                                                    \
+  [FOLLY_SDT_S##n] "n"                ((size_t)FOLLY_SDT_ARGSIZE(x)),          \
+  [FOLLY_SDT_A##n] FOLLY_SDT_ARG_CONSTRAINT (x)
+
+// Templates to append arguments as operands.
+#define FOLLY_SDT_OPERANDS_0()        [__sdt_dummy] "g" (0)
+#define FOLLY_SDT_OPERANDS_1(_1)      FOLLY_SDT_ARG(1, _1)
+#define FOLLY_SDT_OPERANDS_2(_1, _2)                                           \
+  FOLLY_SDT_OPERANDS_1(_1), FOLLY_SDT_ARG(2, _2)
+#define FOLLY_SDT_OPERANDS_3(_1, _2, _3)                                       \
+  FOLLY_SDT_OPERANDS_2(_1, _2), FOLLY_SDT_ARG(3, _3)
+#define FOLLY_SDT_OPERANDS_4(_1, _2, _3, _4)                                   \
+  FOLLY_SDT_OPERANDS_3(_1, _2, _3), FOLLY_SDT_ARG(4, _4)
+#define FOLLY_SDT_OPERANDS_5(_1, _2, _3, _4, _5)                               \
+  FOLLY_SDT_OPERANDS_4(_1, _2, _3, _4), FOLLY_SDT_ARG(5, _5)
+#define FOLLY_SDT_OPERANDS_6(_1, _2, _3, _4, _5, _6)                           \
+  FOLLY_SDT_OPERANDS_5(_1, _2, _3, _4, _5), FOLLY_SDT_ARG(6, _6)
+#define FOLLY_SDT_OPERANDS_7(_1, _2, _3, _4, _5, _6, _7)                       \
+  FOLLY_SDT_OPERANDS_6(_1, _2, _3, _4, _5, _6), FOLLY_SDT_ARG(7, _7)
+#define FOLLY_SDT_OPERANDS_8(_1, _2, _3, _4, _5, _6, _7, _8)                   \
+  FOLLY_SDT_OPERANDS_7(_1, _2, _3, _4, _5, _6, _7), FOLLY_SDT_ARG(8, _8)
+
+// Templates to reference the arguments from operands in note section.
+#define FOLLY_SDT_ARGFMT(no)        %n[FOLLY_SDT_S##no]@%[FOLLY_SDT_A##no]
+#define FOLLY_SDT_ARG_TEMPLATE_0    /*No arguments*/
+#define FOLLY_SDT_ARG_TEMPLATE_1    FOLLY_SDT_ARGFMT(1)
+#define FOLLY_SDT_ARG_TEMPLATE_2    FOLLY_SDT_ARG_TEMPLATE_1 FOLLY_SDT_ARGFMT(2)
+#define FOLLY_SDT_ARG_TEMPLATE_3    FOLLY_SDT_ARG_TEMPLATE_2 FOLLY_SDT_ARGFMT(3)
+#define FOLLY_SDT_ARG_TEMPLATE_4    FOLLY_SDT_ARG_TEMPLATE_3 FOLLY_SDT_ARGFMT(4)
+#define FOLLY_SDT_ARG_TEMPLATE_5    FOLLY_SDT_ARG_TEMPLATE_4 FOLLY_SDT_ARGFMT(5)
+#define FOLLY_SDT_ARG_TEMPLATE_6    FOLLY_SDT_ARG_TEMPLATE_5 FOLLY_SDT_ARGFMT(6)
+#define FOLLY_SDT_ARG_TEMPLATE_7    FOLLY_SDT_ARG_TEMPLATE_6 FOLLY_SDT_ARGFMT(7)
+#define FOLLY_SDT_ARG_TEMPLATE_8    FOLLY_SDT_ARG_TEMPLATE_7 FOLLY_SDT_ARGFMT(8)
+
+// Structure of note section for the probe.
+#define FOLLY_SDT_NOTE_CONTENT(provider, name, arg_template)                   \
+  FOLLY_SDT_ASM_1(990: FOLLY_SDT_NOP)                                          \
+  FOLLY_SDT_ASM_3(     .pushsection .note.stapsdt,"","note")                   \
+  FOLLY_SDT_ASM_1(     .balign 4)                                              \
+  FOLLY_SDT_ASM_3(     .4byte 992f-991f, 994f-993f, FOLLY_SDT_NOTE_TYPE)       \
+  FOLLY_SDT_ASM_1(991: .asciz FOLLY_SDT_NOTE_NAME)                             \
+  FOLLY_SDT_ASM_1(992: .balign 4)                                              \
+  FOLLY_SDT_ASM_1(993: FOLLY_SDT_ASM_ADDR 990b)                                \
+  FOLLY_SDT_ASM_1(     FOLLY_SDT_ASM_ADDR 0) /*Reserved for Semaphore address*/\
+  FOLLY_SDT_ASM_1(     FOLLY_SDT_ASM_ADDR 0) /*Reserved for Semaphore name*/   \
+  FOLLY_SDT_ASM_STRING(provider)                                               \
+  FOLLY_SDT_ASM_STRING(name)                                                   \
+  FOLLY_SDT_ASM_STRING(arg_template)                                           \
+  FOLLY_SDT_ASM_1(994: .balign 4)                                              \
+  FOLLY_SDT_ASM_1(     .popsection)
+
+// Main probe Macro.
+#define FOLLY_SDT_PROBE(provider, name, n, arglist)                            \
+    __asm__ __volatile__ (                                                     \
+      FOLLY_SDT_NOTE_CONTENT(provider, name, FOLLY_SDT_ARG_TEMPLATE_##n)       \
+      :: FOLLY_SDT_OPERANDS_##n arglist                                        \
+    )                                                                          \
+
+// Helper Macros to handle variadic arguments.
+#define FOLLY_SDT_NARG_(_0, _1, _2, _3, _4, _5, _6, _7, _8, N, ...) N
+#define FOLLY_SDT_NARG(...)                                                    \
+  FOLLY_SDT_NARG_(__VA_ARGS__, 8, 7, 6, 5, 4, 3, 2, 1, 0)
+#define FOLLY_SDT_PROBE_N(provider, name, N, ...)                              \
+  FOLLY_SDT_PROBE(provider, name, N, (__VA_ARGS__))

folly/tracing/StaticTracepoint.h

+/*
+ * Copyright 2016 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#if defined(__ELF__) && (defined(__x86_64__) || defined(__i386__))
+#include <folly/tracing/StaticTracepoint-ELFx86.h>
+
+#define FOLLY_SDT(provider, name, ...)                                         \
+  FOLLY_SDT_PROBE_N(                                                           \
+    provider, name, FOLLY_SDT_NARG(0, ##__VA_ARGS__), ##__VA_ARGS__)
+#else
+#define FOLLY_SDT(provider, name, ...) do {} while(0)
+#endif