src/cmd/godefs/main.c - go - Git at Google

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 // Godefs takes as input a host-compilable C file that includes
 // standard system headers.  From that input file, it generates
 // a standalone (no #includes) C or Go file containing equivalent
 // definitions.
 //
 // The input C file is expected to define new types and enumerated
 // constants whose names begin with $ (a legal identifier character
 // in gcc).  The output is the standalone definitions of those names,
 // with the $ removed.
 //
 // For example, if this is x.c:
 //
 //	#include <sys/stat.h>
 //
 //	typedef struct timespec $Timespec;
 //	typedef struct stat $Stat;
 //	enum {
 //		$S_IFMT = S_IFMT,
 //		$S_IFIFO = S_IFIFO,
 //		$S_IFCHR = S_IFCHR,
 //	};
 //
 // then "godefs x.c" generates:
 //
 //	// godefs x.c
 //
 //	// MACHINE GENERATED - DO NOT EDIT.
 //
 //	// Constants
 //	enum {
 //		S_IFMT = 0xf000,
 //		S_IFIFO = 0x1000,
 //		S_IFCHR = 0x2000,
 //	};
 //
 //	// Types
 //	#pragma pack on
 //
 //	typedef struct Timespec Timespec;
 //	struct Timespec {
 //		int32 tv_sec;
 //		int32 tv_nsec;
 //	};
 //
 //	typedef struct Stat Stat;
 //	struct Stat {
 //		int32 st_dev;
 //		uint32 st_ino;
 //		uint16 st_mode;
 //		uint16 st_nlink;
 //		uint32 st_uid;
 //		uint32 st_gid;
 //		int32 st_rdev;
 //		Timespec st_atimespec;
 //		Timespec st_mtimespec;
 //		Timespec st_ctimespec;
 //		int64 st_size;
 //		int64 st_blocks;
 //		int32 st_blksize;
 //		uint32 st_flags;
 //		uint32 st_gen;
 //		int32 st_lspare;
 //		int64 st_qspare[2];
 //	};
 //	#pragma pack off
 //
 // The -g flag to godefs causes it to generate Go output, not C.
 // In the Go output, struct fields have leading xx_ prefixes removed
 // and the first character capitalized (exported).
 //
 // Godefs works by invoking gcc to compile the given input file
 // and then parses the debug info embedded in the assembly output.
 // This is far easier than reading system headers on most machines.
 //
 // The -c flag sets the compiler (default "gcc").
 //
 // The -f flag adds a flag to pass to the compiler (e.g., -f -m64).

 #include "a.h"

 void
 usage(void)
 {
 	fprint(2, "usage: godefs [-g package] [-c cc] [-f cc-arg] [defs.c ...]\n");
 	exit(1);
 }

 int gotypefmt(Fmt*);
 int ctypefmt(Fmt*);
 int prefixlen(Type*);
 int cutprefix(char*);

 Lang go =
 {
 	"const (\n",
 	"\t%s = %#llx;\n",
 	")\n",

 	"type",

 	"type %s struct {\n",
 	"type %s struct {\n",
 	"\tPad%d [%d]byte;\n",
 	"}\n",

 	gotypefmt,
 };

 Lang c =
 {
 	"enum {\n",
 	"\t%s = %#llx,\n",
 	"};\n",

 	"typedef",

 	"typedef struct %s %s;\nstruct %s {\n",
 	"typedef union %s %s;\nunion %s {\n",
 	"\tbyte pad%d[%d];\n",
 	"};\n",

 	ctypefmt,
 };

 char *pkg;

 int oargc;
 char **oargv;
 Lang *lang = &c;

 Const *con;
 int ncon;

 Type **typ;
 int ntyp;

 void
 waitforgcc(void)
 {
 	waitpid();
 }

 void
 main(int argc, char **argv)
 {
 	int p[2], pid, i, j, n, off, npad, prefix;
 	char **av, *q, *r, *tofree, *name;
 	char nambuf[100];
 	Biobuf *bin, *bout;
 	Type *t;
 	Field *f;

 	quotefmtinstall();

 	oargc = argc;
 	oargv = argv;
 	av = emalloc((30+argc)*sizeof av[0]);
 	atexit(waitforgcc);

 	n = 0;
 	av[n++] = "gcc";
 	av[n++] = "-fdollars-in-identifiers";
 	av[n++] = "-S";	// write assembly
 	av[n++] = "-gstabs";	// include stabs info
 	av[n++] = "-o";	// to ...
 	av[n++] = "-";	// ... stdout
 	av[n++] = "-xc";	// read C

 	ARGBEGIN{
 	case 'g':
 		lang = &go;
 		pkg = EARGF(usage());
 		break;
 	case 'c':
 		av[0] = EARGF(usage());
 		break;
 	case 'f':
 		av[n++] = EARGF(usage());
 		break;
 	default:
 		usage();
 	}ARGEND

 	if(argc == 0)
 		av[n++] = "-";
 	else
 		av[n++] = argv[0];
 	av[n] = nil;

 	// Run gcc writing assembly and stabs debugging to p[1].
 	if(pipe(p) < 0)
 		sysfatal("pipe: %r");

 	pid = fork();
 	if(pid < 0)
 		sysfatal("fork: %r");
 	if(pid == 0) {
 		close(p[0]);
 		dup(p[1], 1);
 		if(argc == 0) {
 			exec(av[0], av);
 			fprint(2, "exec gcc: %r\n");
 			exit(1);
 		}
 		// Some versions of gcc do not accept -S with multiple files.
 		// Run gcc once for each file.
 		close(0);
 		open("/dev/null", OREAD);
 		for(i=0; i<argc; i++) {
 			pid = fork();
 			if(pid < 0)
 				sysfatal("fork: %r");
 			if(pid == 0) {
 				av[n-1] = argv[i];
 				exec(av[0], av);
 				fprint(2, "exec gcc: %r\n");
 				exit(1);
 			}
 			waitpid();
 		}
 		exit(0);
 	}
 	close(p[1]);

 	// Read assembly, pulling out .stabs lines.
 	bin = Bfdopen(p[0], OREAD);
 	while((q = Brdstr(bin, '\n', 1)) != nil) {
 		//	.stabs	"float:t(0,12)=r(0,1);4;0;",128,0,0,0
 		tofree = q;
 		while(*q == ' ' || *q == '\t')
 			q++;
 		if(strncmp(q, ".stabs", 6) != 0)
 			goto Continue;
 		q += 6;
 		while(*q == ' ' || *q == '\t')
 			q++;
 		if(*q++ != '\"') {
 		Bad:
 			sysfatal("cannot parse .stabs line:\n%s", tofree);
 		}

 		r = strchr(q, '\"');
 		if(r == nil)
 			goto Bad;
 		*r++ = '\0';
 		if(*r++ != ',')
 			goto Bad;
 		if(*r < '0' || *r > '9')
 			goto Bad;
 		if(atoi(r) != 128)	// stabs kind = local symbol
 			goto Continue;

 		parsestabtype(q);

 	Continue:
 		free(tofree);
 	}
 	Bterm(bin);
 	waitpid();

 	// Write defs to standard output.
 	bout = Bfdopen(1, OWRITE);
 	fmtinstall('T', lang->typefmt);

 	// Echo original command line in header.
 	Bprint(bout, "//");
 	for(i=0; i<oargc; i++)
 		Bprint(bout, " %q", oargv[i]);
 	Bprint(bout, "\n");
 	Bprint(bout, "\n");
 	Bprint(bout, "// MACHINE GENERATED - DO NOT EDIT.\n");
 	Bprint(bout, "\n");

 	if(pkg)
 		Bprint(bout, "package %s\n\n", pkg);

 	// Constants.
 	Bprint(bout, "// Constants\n");
 	if(ncon > 0) {
 		Bprint(bout, lang->constbegin);
 		for(i=0; i<ncon; i++)
 			Bprint(bout, lang->constfmt, con[i].name, con[i].value);
 		Bprint(bout, lang->constend);
 	}
 	Bprint(bout, "\n");

 	// Types

 	// push our names down
 	for(i=0; i<ntyp; i++) {
 		t = typ[i];
 		name = t->name;
 		while(t && t->kind == Typedef)
 			t = t->type;
 		if(t)
 			t->name = name;
 	}

 	Bprint(bout, "// Types\n");

 	// Have to turn off structure padding in Plan 9 compiler,
 	// mainly because it is more aggressive than gcc tends to be.
 	if(lang == &c)
 		Bprint(bout, "#pragma pack on\n");

 	for(i=0; i<ntyp; i++) {
 		Bprint(bout, "\n");
 		t = typ[i];
 		name = t->name;
 		while(t && t->kind == Typedef) {
 			if(name == nil && t->name != nil) {
 				name = t->name;
 				if(t->printed)
 					break;
 			}
 			t = t->type;
 		}
 		if(name == nil && t->name != nil) {
 			name = t->name;
 			if(t->printed)
 				continue;
 			t->printed = 1;
 		}
 		if(name == nil) {
 			fprint(2, "unknown name for %T", typ[i]);
 			continue;
 		}
 		if(name[0] == '$')
 			name++;
 		npad = 0;
 		off = 0;
 		switch(t->kind) {
 		case 0:
 			fprint(2, "unknown type definition for %s\n", name);
 			break;
 		default:	// numeric, array, or pointer
 		case Array:
 		case Ptr:
 			Bprint(bout, "%s %lT\n", lang->typdef, name, t);
 			break;
 		case Union:
 			// In Go, print union as struct with only first element,
 			// padded the rest of the way.
 			Bprint(bout, lang->unionbegin, name, name, name);
 			goto StructBody;
 		case Struct:
 			Bprint(bout, lang->structbegin, name, name, name);
 		StructBody:
 			prefix = 0;
 			if(lang == &go)
 				prefix = prefixlen(t);
 			for(j=0; j<t->nf; j++) {
 				f = &t->f[j];
 				// padding
 				if(t->kind == Struct || lang == &go) {
 					if(f->offset%8 != 0 || f->size%8 != 0) {
 						fprint(2, "ignoring bitfield %s.%s\n", t->name, f->name);
 						continue;
 					}
 					if(f->offset < off)
 						sysfatal("%s: struct fields went backward", t->name);
 					if(off < f->offset) {
 						Bprint(bout, lang->structpadfmt, npad++, (f->offset - off) / 8);
 						off = f->offset;
 					}
 					off += f->size;
 				}
 				name = f->name;
 				if(cutprefix(name))
 					name += prefix;
 				if(strcmp(name, "") == 0) {
 					snprint(nambuf, sizeof nambuf, "Pad%d", npad++);
 					name = nambuf;
 				}
 				Bprint(bout, "\t%#lT;\n", name, f->type);
 				if(t->kind == Union && lang == &go)
 					break;
 			}
 			// final padding
 			if(t->kind == Struct || lang == &go) {
 				if(off/8 < t->size)
 					Bprint(bout, lang->structpadfmt, npad++, t->size - off/8);
 			}
 			Bprint(bout, lang->structend);
 		}
 	}
 	if(lang == &c)
 		Bprint(bout, "#pragma pack off\n");
 	Bterm(bout);
 	exit(0);
 }

 char *kindnames[] = {
 	"void",	// actually unknown, but byte is good for pointers
 	"void",
 	"int8",
 	"uint8",
 	"int16",
 	"uint16",
 	"int32",
 	"uint32",
 	"int64",
 	"uint64",
 	"float32",
 	"float64",
 	"ptr",
 	"struct",
 	"array",
 	"union",
 	"typedef",
 };

 int
 ctypefmt(Fmt *f)
 {
 	char *name, *s;
 	Type *t;

 	name = nil;
 	if(f->flags & FmtLong) {
 		name = va_arg(f->args, char*);
 		if(name == nil || name[0] == '\0')
 			name = "_anon_";
 	}
 	t = va_arg(f->args, Type*);
 	while(t && t->kind == Typedef)
 		t = t->type;
 	switch(t->kind) {
 	case Struct:
 	case Union:
 		// must be named
 		s = t->name;
 		if(s == nil) {
 			fprint(2, "need name for anonymous struct\n");
 			goto bad;
 		}
 		else if(s[0] != '$')
 			fprint(2, "need name for struct %s\n", s);
 		else
 			s++;
 		fmtprint(f, "%s", s);
 		if(name)
 			fmtprint(f, " %s", name);
 		break;

 	case Array:
 		if(name)
 			fmtprint(f, "%T %s[%d]", t->type, name, t->size);
 		else
 			fmtprint(f, "%T[%d]", t->type, t->size);
 		break;

 	case Ptr:
 		if(name)
 			fmtprint(f, "%T *%s", t->type, name);
 		else
 			fmtprint(f, "%T*", t->type);
 		break;

 	default:
 		fmtprint(f, "%s", kindnames[t->kind]);
 		if(name)
 			fmtprint(f, " %s", name);
 		break;

 	bad:
 		if(name)
 			fmtprint(f, "byte %s[%d]", name, t->size);
 		else
 			fmtprint(f, "byte[%d]", t->size);
 		break;
 	}

 	return 0;
 }

 int
 gotypefmt(Fmt *f)
 {
 	char *name, *s;
 	Type *t;

 	if(f->flags & FmtLong) {
 		name = va_arg(f->args, char*);
 		if('a' <= name[0] && name[0] <= 'z')
 			name[0] += 'A' - 'a';
 		if(name[0] == '_' && (f->flags & FmtSharp))
 			fmtprint(f, "X");
 		fmtprint(f, "%s ", name);
 	}
 	t = va_arg(f->args, Type*);
 	while(t && t->kind == Typedef)
 		t = t->type;

 	switch(t->kind) {
 	case Struct:
 	case Union:
 		// must be named
 		s = t->name;
 		if(s == nil) {
 			fprint(2, "need name for anonymous struct\n");
 			fmtprint(f, "STRUCT");
 		}
 		else if(s[0] != '$') {
 			fprint(2, "warning: missing name for struct %s\n", s);
 			fmtprint(f, "[%d]byte /* %s */", t->size, s);
 		} else
 			fmtprint(f, "%s", s+1);
 		break;

 	case Array:
 		fmtprint(f, "[%d]%T", t->size, t->type);
 		break;

 	case Ptr:
 		fmtprint(f, "*%T", t->type);
 		break;

 	default:
 		s = kindnames[t->kind];
 		if(strcmp(s, "void") == 0)
 			s = "byte";
 		fmtprint(f, "%s", s);
 	}

 	return 0;
 }

 // Is this the kind of name we should cut a prefix from?
 // The rule is that the name cannot begin with underscore
 // and must have an underscore eventually.
 int
 cutprefix(char *name)
 {
 	char *p;

 	// special case: orig_ in register struct
 	if(strncmp(name, "orig_", 5) == 0)
 		return 0;

 	for(p=name; *p; p++) {
 		if(*p == '_')
 			return p-name > 0;
 	}
 	return 0;
 }

 // Figure out common struct prefix len
 int
 prefixlen(Type *t)
 {
 	int i;
 	int len;
 	char *p, *name;
 	Field *f;

 	len = 0;
 	name = nil;
 	for(i=0; i<t->nf; i++) {
 		f = &t->f[i];
 		if(!cutprefix(f->name))
 			continue;
 		p = strchr(f->name, '_');
 		if(p == nil)
 			return 0;
 		if(name == nil) {
 			name = f->name;
 			len = p+1 - name;
 		}
 		else if(strncmp(f->name, name, len) != 0)
 			return 0;
 	}
 	return len;
 }
	// Copyright 2009 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	// Godefs takes as input a host-compilable C file that includes
	// standard system headers. From that input file, it generates
	// a standalone (no #includes) C or Go file containing equivalent
	// definitions.
	//
	// The input C file is expected to define new types and enumerated
	// constants whose names begin with $ (a legal identifier character
	// in gcc). The output is the standalone definitions of those names,
	// with the $ removed.
	//
	// For example, if this is x.c:
	//
	// #include <sys/stat.h>
	//
	// typedef struct timespec $Timespec;
	// typedef struct stat $Stat;
	// enum {
	// $S_IFMT = S_IFMT,
	// $S_IFIFO = S_IFIFO,
	// $S_IFCHR = S_IFCHR,
	// };
	//
	// then "godefs x.c" generates:
	//
	// // godefs x.c
	//
	// // MACHINE GENERATED - DO NOT EDIT.
	//
	// // Constants
	// enum {
	// S_IFMT = 0xf000,
	// S_IFIFO = 0x1000,
	// S_IFCHR = 0x2000,
	// };
	//
	// // Types
	// #pragma pack on
	//
	// typedef struct Timespec Timespec;
	// struct Timespec {
	// int32 tv_sec;
	// int32 tv_nsec;
	// };
	//
	// typedef struct Stat Stat;
	// struct Stat {
	// int32 st_dev;
	// uint32 st_ino;
	// uint16 st_mode;
	// uint16 st_nlink;
	// uint32 st_uid;
	// uint32 st_gid;
	// int32 st_rdev;
	// Timespec st_atimespec;
	// Timespec st_mtimespec;
	// Timespec st_ctimespec;
	// int64 st_size;
	// int64 st_blocks;
	// int32 st_blksize;
	// uint32 st_flags;
	// uint32 st_gen;
	// int32 st_lspare;
	// int64 st_qspare[2];
	// };
	// #pragma pack off
	//
	// The -g flag to godefs causes it to generate Go output, not C.
	// In the Go output, struct fields have leading xx_ prefixes removed
	// and the first character capitalized (exported).
	//
	// Godefs works by invoking gcc to compile the given input file
	// and then parses the debug info embedded in the assembly output.
	// This is far easier than reading system headers on most machines.
	//
	// The -c flag sets the compiler (default "gcc").
	//
	// The -f flag adds a flag to pass to the compiler (e.g., -f -m64).

	#include "a.h"

	void
	usage(void)
	{
	fprint(2, "usage: godefs [-g package] [-c cc] [-f cc-arg] [defs.c ...]\n");
	exit(1);
	}

	int gotypefmt(Fmt*);
	int ctypefmt(Fmt*);
	int prefixlen(Type*);
	int cutprefix(char*);

	Lang go =
	{
	"const (\n",
	"\t%s = %#llx;\n",
	")\n",

	"type",

	"type %s struct {\n",
	"type %s struct {\n",
	"\tPad%d [%d]byte;\n",
	"}\n",

	gotypefmt,
	};

	Lang c =
	{
	"enum {\n",
	"\t%s = %#llx,\n",
	"};\n",

	"typedef",

	"typedef struct %s %s;\nstruct %s {\n",
	"typedef union %s %s;\nunion %s {\n",
	"\tbyte pad%d[%d];\n",
	"};\n",

	ctypefmt,
	};

	char *pkg;

	int oargc;
	char **oargv;
	Lang *lang = &c;

	Const *con;
	int ncon;

	Type **typ;
	int ntyp;

	void
	waitforgcc(void)
	{
	waitpid();
	}

	void
	main(int argc, char **argv)
	{
	int p[2], pid, i, j, n, off, npad, prefix;
	char *av, q, r, tofree, *name;
	char nambuf[100];
	Biobuf bin, bout;
	Type *t;
	Field *f;

	quotefmtinstall();

	oargc = argc;
	oargv = argv;
	av = emalloc((30+argc)*sizeof av[0]);
	atexit(waitforgcc);

	n = 0;
	av[n++] = "gcc";
	av[n++] = "-fdollars-in-identifiers";
	av[n++] = "-S"; // write assembly
	av[n++] = "-gstabs"; // include stabs info
	av[n++] = "-o"; // to ...
	av[n++] = "-"; // ... stdout
	av[n++] = "-xc"; // read C

	ARGBEGIN{
	case 'g':
	lang = &go;
	pkg = EARGF(usage());
	break;
	case 'c':
	av[0] = EARGF(usage());
	break;
	case 'f':
	av[n++] = EARGF(usage());
	break;
	default:
	usage();
	}ARGEND

	if(argc == 0)
	av[n++] = "-";
	else
	av[n++] = argv[0];
	av[n] = nil;

	// Run gcc writing assembly and stabs debugging to p[1].
	if(pipe(p) < 0)
	sysfatal("pipe: %r");

	pid = fork();
	if(pid < 0)
	sysfatal("fork: %r");
	if(pid == 0) {
	close(p[0]);
	dup(p[1], 1);
	if(argc == 0) {
	exec(av[0], av);
	fprint(2, "exec gcc: %r\n");
	exit(1);
	}
	// Some versions of gcc do not accept -S with multiple files.
	// Run gcc once for each file.
	close(0);
	open("/dev/null", OREAD);
	for(i=0; i<argc; i++) {
	pid = fork();
	if(pid < 0)
	sysfatal("fork: %r");
	if(pid == 0) {
	av[n-1] = argv[i];
	exec(av[0], av);
	fprint(2, "exec gcc: %r\n");
	exit(1);
	}
	waitpid();
	}
	exit(0);
	}
	close(p[1]);

	// Read assembly, pulling out .stabs lines.
	bin = Bfdopen(p[0], OREAD);
	while((q = Brdstr(bin, '\n', 1)) != nil) {
	// .stabs "float:t(0,12)=r(0,1);4;0;",128,0,0,0
	tofree = q;
	while(q == ' ' \|\| q == '\t')
	q++;
	if(strncmp(q, ".stabs", 6) != 0)
	goto Continue;
	q += 6;
	while(q == ' ' \|\| q == '\t')
	q++;
	if(*q++ != '\"') {
	Bad:
	sysfatal("cannot parse .stabs line:\n%s", tofree);
	}

	r = strchr(q, '\"');
	if(r == nil)
	goto Bad;
	*r++ = '\0';
	if(*r++ != ',')
	goto Bad;
	if(r < '0' \|\| r > '9')
	goto Bad;
	if(atoi(r) != 128) // stabs kind = local symbol
	goto Continue;

	parsestabtype(q);

	Continue:
	free(tofree);
	}
	Bterm(bin);
	waitpid();

	// Write defs to standard output.
	bout = Bfdopen(1, OWRITE);
	fmtinstall('T', lang->typefmt);

	// Echo original command line in header.
	Bprint(bout, "//");
	for(i=0; i<oargc; i++)
	Bprint(bout, " %q", oargv[i]);
	Bprint(bout, "\n");
	Bprint(bout, "\n");
	Bprint(bout, "// MACHINE GENERATED - DO NOT EDIT.\n");
	Bprint(bout, "\n");

	if(pkg)
	Bprint(bout, "package %s\n\n", pkg);

	// Constants.
	Bprint(bout, "// Constants\n");
	if(ncon > 0) {
	Bprint(bout, lang->constbegin);
	for(i=0; i<ncon; i++)
	Bprint(bout, lang->constfmt, con[i].name, con[i].value);
	Bprint(bout, lang->constend);
	}
	Bprint(bout, "\n");

	// Types

	// push our names down
	for(i=0; i<ntyp; i++) {
	t = typ[i];
	name = t->name;
	while(t && t->kind == Typedef)
	t = t->type;
	if(t)
	t->name = name;
	}

	Bprint(bout, "// Types\n");

	// Have to turn off structure padding in Plan 9 compiler,
	// mainly because it is more aggressive than gcc tends to be.
	if(lang == &c)
	Bprint(bout, "#pragma pack on\n");

	for(i=0; i<ntyp; i++) {
	Bprint(bout, "\n");
	t = typ[i];
	name = t->name;
	while(t && t->kind == Typedef) {
	if(name == nil && t->name != nil) {
	name = t->name;
	if(t->printed)
	break;
	}
	t = t->type;
	}
	if(name == nil && t->name != nil) {
	name = t->name;
	if(t->printed)
	continue;
	t->printed = 1;
	}
	if(name == nil) {
	fprint(2, "unknown name for %T", typ[i]);
	continue;
	}
	if(name[0] == '$')
	name++;
	npad = 0;
	off = 0;
	switch(t->kind) {
	case 0:
	fprint(2, "unknown type definition for %s\n", name);
	break;
	default: // numeric, array, or pointer
	case Array:
	case Ptr:
	Bprint(bout, "%s %lT\n", lang->typdef, name, t);
	break;
	case Union:
	// In Go, print union as struct with only first element,
	// padded the rest of the way.
	Bprint(bout, lang->unionbegin, name, name, name);
	goto StructBody;
	case Struct:
	Bprint(bout, lang->structbegin, name, name, name);
	StructBody:
	prefix = 0;
	if(lang == &go)
	prefix = prefixlen(t);
	for(j=0; j<t->nf; j++) {
	f = &t->f[j];
	// padding
	if(t->kind == Struct \|\| lang == &go) {
	if(f->offset%8 != 0 \|\| f->size%8 != 0) {
	fprint(2, "ignoring bitfield %s.%s\n", t->name, f->name);
	continue;
	}
	if(f->offset < off)
	sysfatal("%s: struct fields went backward", t->name);
	if(off < f->offset) {
	Bprint(bout, lang->structpadfmt, npad++, (f->offset - off) / 8);
	off = f->offset;
	}
	off += f->size;
	}
	name = f->name;
	if(cutprefix(name))
	name += prefix;
	if(strcmp(name, "") == 0) {
	snprint(nambuf, sizeof nambuf, "Pad%d", npad++);
	name = nambuf;
	}
	Bprint(bout, "\t%#lT;\n", name, f->type);
	if(t->kind == Union && lang == &go)
	break;
	}
	// final padding
	if(t->kind == Struct \|\| lang == &go) {
	if(off/8 < t->size)
	Bprint(bout, lang->structpadfmt, npad++, t->size - off/8);
	}
	Bprint(bout, lang->structend);
	}
	}
	if(lang == &c)
	Bprint(bout, "#pragma pack off\n");
	Bterm(bout);
	exit(0);
	}

	char *kindnames[] = {
	"void", // actually unknown, but byte is good for pointers
	"void",
	"int8",
	"uint8",
	"int16",
	"uint16",
	"int32",
	"uint32",
	"int64",
	"uint64",
	"float32",
	"float64",
	"ptr",
	"struct",
	"array",
	"union",
	"typedef",
	};

	int
	ctypefmt(Fmt *f)
	{
	char name, s;
	Type *t;

	name = nil;
	if(f->flags & FmtLong) {
	name = va_arg(f->args, char*);
	if(name == nil \|\| name[0] == '\0')
	name = "_anon_";
	}
	t = va_arg(f->args, Type*);
	while(t && t->kind == Typedef)
	t = t->type;
	switch(t->kind) {
	case Struct:
	case Union:
	// must be named
	s = t->name;
	if(s == nil) {
	fprint(2, "need name for anonymous struct\n");
	goto bad;
	}
	else if(s[0] != '$')
	fprint(2, "need name for struct %s\n", s);
	else
	s++;
	fmtprint(f, "%s", s);
	if(name)
	fmtprint(f, " %s", name);
	break;

	case Array:
	if(name)
	fmtprint(f, "%T %s[%d]", t->type, name, t->size);
	else
	fmtprint(f, "%T[%d]", t->type, t->size);
	break;

	case Ptr:
	if(name)
	fmtprint(f, "%T *%s", t->type, name);
	else
	fmtprint(f, "%T*", t->type);
	break;

	default:
	fmtprint(f, "%s", kindnames[t->kind]);
	if(name)
	fmtprint(f, " %s", name);
	break;

	bad:
	if(name)
	fmtprint(f, "byte %s[%d]", name, t->size);
	else
	fmtprint(f, "byte[%d]", t->size);
	break;
	}

	return 0;
	}

	int
	gotypefmt(Fmt *f)
	{
	char name, s;
	Type *t;

	if(f->flags & FmtLong) {
	name = va_arg(f->args, char*);
	if('a' <= name[0] && name[0] <= 'z')
	name[0] += 'A' - 'a';
	if(name[0] == '_' && (f->flags & FmtSharp))
	fmtprint(f, "X");
	fmtprint(f, "%s ", name);
	}
	t = va_arg(f->args, Type*);
	while(t && t->kind == Typedef)
	t = t->type;

	switch(t->kind) {
	case Struct:
	case Union:
	// must be named
	s = t->name;
	if(s == nil) {
	fprint(2, "need name for anonymous struct\n");
	fmtprint(f, "STRUCT");
	}
	else if(s[0] != '$') {
	fprint(2, "warning: missing name for struct %s\n", s);
	fmtprint(f, "[%d]byte /* %s */", t->size, s);
	} else
	fmtprint(f, "%s", s+1);
	break;

	case Array:
	fmtprint(f, "[%d]%T", t->size, t->type);
	break;

	case Ptr:
	fmtprint(f, "*%T", t->type);
	break;

	default:
	s = kindnames[t->kind];
	if(strcmp(s, "void") == 0)
	s = "byte";
	fmtprint(f, "%s", s);
	}

	return 0;
	}

	// Is this the kind of name we should cut a prefix from?
	// The rule is that the name cannot begin with underscore
	// and must have an underscore eventually.
	int
	cutprefix(char *name)
	{
	char *p;

	// special case: orig_ in register struct
	if(strncmp(name, "orig_", 5) == 0)
	return 0;

	for(p=name; *p; p++) {
	if(*p == '_')
	return p-name > 0;
	}
	return 0;
	}

	// Figure out common struct prefix len
	int
	prefixlen(Type *t)
	{
	int i;
	int len;
	char p, name;
	Field *f;

	len = 0;
	name = nil;
	for(i=0; i<t->nf; i++) {
	f = &t->f[i];
	if(!cutprefix(f->name))
	continue;
	p = strchr(f->name, '_');
	if(p == nil)
	return 0;
	if(name == nil) {
	name = f->name;
	len = p+1 - name;
	}
	else if(strncmp(f->name, name, len) != 0)
	return 0;
	}
	return len;
	}