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Diffstat (limited to 'lib/xref.h')
| -rw-r--r-- | lib/xref.h | 231 |
1 files changed, 231 insertions, 0 deletions
diff --git a/lib/xref.h b/lib/xref.h new file mode 100644 index 0000000000..8cfe6a3b38 --- /dev/null +++ b/lib/xref.h @@ -0,0 +1,231 @@ +/* + * Copyright (c) 2017-20 David Lamparter, for NetDEF, Inc. + * + * Permission to use, copy, modify, and distribute this software for any + * purpose with or without fee is hereby granted, provided that the above + * copyright notice and this permission notice appear in all copies. + * + * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES + * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF + * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR + * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES + * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN + * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF + * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. + */ + +#ifndef _FRR_XREF_H +#define _FRR_XREF_H + +#include <stdint.h> +#include <stdlib.h> +#include <limits.h> +#include <errno.h> +#include "compiler.h" + +enum xref_type { + XREFT_NONE = 0, +}; + +/* struct xref is the "const" part; struct xrefdata is the writable part. */ +struct xref; +struct xrefdata; + +struct xref { + /* this may be NULL, depending on the type of the xref. + * if it is NULL, the xref has no unique ID and cannot be accessed + * through that mechanism. + */ + struct xrefdata *xrefdata; + + /* type isn't generally needed at runtime */ + enum xref_type type; + + /* code location */ + int line; + const char *file; + const char *func; + + /* -- 32 bytes (on 64bit) -- */ + + /* type-specific bits appended by embedding this struct */ +}; + +struct xrefdata { + /* pointer back to the const part; this will be initialized at + * program startup by xref_block_add(). (Creating structs with + * cyclic pointers to each other is not easily possible for + * function-scoped static variables.) + * + * There is no xrefdata w/o xref, but there are xref w/o xrefdata. + */ + const struct xref *xref; + + /* base32(crockford) of unique ID. not all bytes are used, but + * let's pad to 16 for simplicity + */ + char uid[16]; + + /* hash/uid input + * if hashstr is NULL, no UID is assigned/calculated. Use macro + * string concatenation if multiple values need to be fed in. + * (This is here to not make the UID calculation independent of + * xref type.) + */ + const char *hashstr; + uint32_t hashu32[2]; + + /* -- 32 bytes (on 64bit) -- */ +}; + +/* linker "magic" is used to create an array of pointers to struct xref. + * the result is a contiguous block of pointers, each pointing to an xref + * somewhere in the code. The linker gives us start and end pointers, we + * stuff those into the struct below and hook up a constructor to run at + * program startup with the struct passed. + * + * Placing the xrefs themselves into an array doesn't work because they'd + * need to be constant size, but we're embedding struct xref into other + * container structs with extra data. Also this means that external code + * (like the python xref dumper) can safely ignore extra data at the end of + * xrefs without needing to account for size in iterating the array. + * + * If you're curious, this is also how __attribute__((constructor)) (and + * destructor) are implemented - there are 2 arrays, ".init_array" and + * ".fini_array", containing function pointers. The magic turns out to be + * quite mundane, actually ;) + * + * The slightly tricky bit is that this is a per-object (i.e. per shared + * library & daemon) thing and we need a bit of help (in XREF_SETUP) to + * initialize correctly. + */ + +struct xref_block { + struct xref_block *next; + const struct xref * const *start; + const struct xref * const *stop; +}; + +extern struct xref_block *xref_blocks; +extern void xref_block_add(struct xref_block *block); + +#ifndef HAVE_SECTION_SYMS +/* we have a build system patch to use GNU ld on Solaris; if that doesn't + * work we end up on Solaris ld which doesn't support the section start/end + * symbols. + */ +#define XREF_SETUP() \ + CPP_NOTICE("Missing linker support for section arrays. Solaris ld?") +#else +/* the actual symbols that the linker provides for us. Note these are + * _symbols_ referring to the actual section start/end, i.e. they are very + * much NOT _pointers_, rather the symbol *value* is the pointer. Declaring + * them as size-1 arrays is the "best" / "right" thing. + */ +extern const struct xref * const __start_xref_array[1] DSO_LOCAL; +extern const struct xref * const __stop_xref_array[1] DSO_LOCAL; + +/* this macro is invoked once for each standalone DSO through + * FRR_MODULE_SETUP \ + * }-> FRR_COREMOD_SETUP -> XREF_SETUP + * FRR_DAEMON_INFO / + */ +#define XREF_SETUP() \ + static const struct xref _dummy_xref = { \ + .file = __FILE__, .line = __LINE__, .func = "dummy", \ + .type = XREFT_NONE, \ + }; \ + static const struct xref * const _dummy_xref_p \ + __attribute__((used, section("xref_array"))) \ + = &_dummy_xref; \ + static void __attribute__((used, _CONSTRUCTOR(1100))) \ + _xref_init(void) { \ + static struct xref_block _xref_block = { \ + .start = __start_xref_array, \ + .stop = __stop_xref_array, \ + }; \ + xref_block_add(&_xref_block); \ + } \ + asm(XREF_NOTE); \ + /* end */ + +/* the following blurb emits an ELF note indicating start and end of the xref + * array in the binary. This is technically the "correct" entry point for + * external tools reading xrefs out of an ELF shared library or executable. + * + * right now, the extraction tools use the section header for "xref_array" + * instead; however, section headers are technically not necessarily preserved + * for fully linked libraries or executables. (In practice they are only + * stripped by obfuscation tools.) + * + * conversely, for reading xrefs out of a single relocatable object file (e.g. + * bar.o), section headers are the right thing to look at since the note is + * only emitted for the final binary once. + * + * FRR itself does not need this note to operate correctly, so if you have + * some build issue with it just add -DFRR_XREF_NO_NOTE to your build flags + * to disable it. + */ +#ifdef FRR_XREF_NO_NOTE +#define XREF_NOTE "" +#else + +#if __SIZEOF_POINTER__ == 4 +#define _NOTE_2PTRSIZE "8" +#define _NOTE_PTR ".long" +#elif __SIZEOF_POINTER__ == 8 +#define _NOTE_2PTRSIZE "16" +#define _NOTE_PTR ".quad" +#else +#error unsupported pointer size +#endif + +#ifdef __arm__ +# define asmspecial "%" +#else +# define asmspecial "@" +#endif + +#define XREF_NOTE \ + "" "\n"\ + " .type _frr_xref_note," asmspecial "object" "\n"\ + " .pushsection .note.FRR,\"a\"," asmspecial "note" "\n"\ + " .p2align 2" "\n"\ + "_frr_xref_note:" "\n"\ + " .long 9" "\n"\ + " .long " _NOTE_2PTRSIZE "\n"\ + " .ascii \"XREF\"" "\n"\ + " .ascii \"FRRouting\\0\\0\\0\"" "\n"\ + " " _NOTE_PTR " __start_xref_array-." "\n"\ + " " _NOTE_PTR " __stop_xref_array-." "\n"\ + " .size _frr_xref_note, .-_frr_xref_note" "\n"\ + " .popsection" "\n"\ + "" "\n"\ + /* end */ +#endif + +#endif /* HAVE_SECTION_SYMS */ + +/* emit the array entry / pointer to xref */ +#define XREF_LINK(dst) \ + static const struct xref * const NAMECTR(xref_p_) \ + __attribute__((used, section("xref_array"))) \ + = &(dst) \ + /* end */ + +/* initializer for a "struct xref" */ +#define XREF_INIT(type_, xrefdata_, func_) \ + { \ + .type = (type_), .xrefdata = (xrefdata_), \ + .file = __FILE__, .line = __LINE__, .func = func_, \ + } \ + /* end */ + +/* use with XREF_INIT when outside of a function, i.e. no __func__ */ +#define XREF_NO_FUNC "<global>" + +#ifdef __cplusplus +} +#endif + +#endif /* _FRR_XREF_H */ |