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IABSD.fr/src/usr.bin/make/arch.c

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  • Author : espie
    Date : 2020-01-13 13:54:44
    Hash : 583c2e1d
    Message : introduce a "Buf_Reinit" function for handling static buffers that can be reused throughout running make. Instead of recreating buffers of dubious appropriate size, have one single buffer for various stages of parsing.

  • usr.bin/make/arch.c
  • /*	$OpenBSD: arch.c,v 1.91 2020/01/13 13:54:44 espie Exp $ */
    /*	$NetBSD: arch.c,v 1.17 1996/11/06 17:58:59 christos Exp $	*/
    
    /*
     * Copyright (c) 1999,2000 Marc Espie.
     *
     * Extensive code changes for the OpenBSD project.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE OPENBSD PROJECT AND CONTRIBUTORS
     * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
     * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
     * A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OPENBSD
     * PROJECT OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
     * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
     * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
     * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     */
    /*
     * Copyright (c) 1988, 1989, 1990, 1993
     *	The Regents of the University of California.  All rights reserved.
     * Copyright (c) 1989 by Berkeley Softworks
     * All rights reserved.
     *
     * This code is derived from software contributed to Berkeley by
     * Adam de Boor.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     */
    
    /*
     *	Once again, cacheing/hashing comes into play in the manipulation
     * of archives. The first time an archive is referenced, all of its members'
     * headers are read and hashed and the archive closed again. All hashed
     * archives are kept in a hash (archives) which is searched each time
     * an archive member is referenced.
     *
     */
    
    #include <ar.h>
    #include <assert.h>
    #include <ctype.h>
    #include <fcntl.h>
    #include <limits.h>
    #include <stddef.h>
    #include <stdint.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #include <unistd.h>
    #include <ohash.h>
    #include "config.h"
    #include "defines.h"
    #include "buf.h"
    #include "dir.h"
    #include "direxpand.h"
    #include "arch.h"
    #include "var.h"
    #include "targ.h"
    #include "memory.h"
    #include "gnode.h"
    #include "timestamp.h"
    #include "lst.h"
    
    #ifdef TARGET_MACHINE
    #undef MACHINE
    #define MACHINE TARGET_MACHINE
    #endif
    #ifdef TARGET_MACHINE_ARCH
    #undef MACHINE_ARCH
    #define MACHINE_ARCH TARGET_MACHINE_ARCH
    #endif
    #ifdef TARGET_MACHINE_CPU
    #undef MACHINE_CPU
    #define MACHINE_CPU TARGET_MACHINE_CPU
    #endif
    
    static struct ohash archives;	/* Archives we've already examined.  */
    
    typedef struct Arch_ {
    	struct ohash members;	/* All the members of this archive, as
    				 * struct arch_member entries.  */
    	char name[1];		/* Archive name. */
    } Arch;
    
    /* Used to get to ar's field sizes.  */
    static struct ar_hdr *dummy;
    #define AR_NAME_SIZE		(sizeof(dummy->ar_name))
    #define AR_DATE_SIZE		(sizeof(dummy->ar_date))
    
    /* Each archive member is tied to an arch_member structure,
     * suitable for hashing.  */
    struct arch_member {
    	struct timespec mtime;		/* Member modification date.  */
    	char date[AR_DATE_SIZE+1];	/* Same, before conversion to numeric
    					 * value.  */
    	char name[1];			/* Member name.  */
    };
    
    static struct ohash_info members_info = {
    	offsetof(struct arch_member, name), NULL,
    	hash_calloc, hash_free, element_alloc
    };
    
    static struct ohash_info arch_info = {
    	offsetof(Arch, name), NULL, hash_calloc, hash_free, element_alloc
    };
    
    
    
    static struct arch_member *new_arch_member(struct ar_hdr *, const char *);
    static struct timespec mtime_of_member(struct arch_member *);
    static long field2long(const char *, size_t);
    static Arch *read_archive(const char *, const char *);
    
    static struct timespec ArchMTimeMember(const char *, const char *, bool);
    static FILE *ArchFindMember(const char *, const char *, struct ar_hdr *, const char *);
    static void ArchTouch(const char *, const char *);
    #if defined(__svr4__) || defined(__SVR4) || \
        (defined(__OpenBSD__) && defined(__ELF__))
    #define SVR4ARCHIVES
    #endif
    static bool parse_archive(Buffer, const char **, Lst, SymTable *);
    static void add_archive_node(Lst, const char *);
    
    struct SVR4namelist {
    	char *fnametab;		/* Extended name table strings */
    	size_t fnamesize;	/* Size of the string table */
    };
    
    #ifdef SVR4ARCHIVES
    static const char *svr4list = "Archive list";
    
    static char *ArchSVR4Entry(struct SVR4namelist *, const char *, size_t, FILE *);
    #endif
    
    static struct arch_member *
    new_arch_member(struct ar_hdr *hdr, const char *name)
    {
    	const char *end = NULL;
    	struct arch_member *n;
    
    	n = ohash_create_entry(&members_info, name, &end);
    	/* XXX ar entries are NOT null terminated.	*/
    	memcpy(n->date, &(hdr->ar_date), AR_DATE_SIZE);
    	n->date[AR_DATE_SIZE] = '\0';
    	/* Don't compute mtime before it is needed. */
    	ts_set_out_of_date(n->mtime);
    	return n;
    }
    
    static struct timespec
    mtime_of_member(struct arch_member *m)
    {
    	if (is_out_of_date(m->mtime))
    		ts_set_from_time_t((time_t) strtoll(m->date, NULL, 10),
    		    m->mtime);
    	return m->mtime;
    }
    
    bool
    Arch_ParseArchive(const char **line, Lst nodes, SymTable *ctxt)
    {
    	bool result;
    	static BUFFER expand;
    
    	Buf_Reinit(&expand, MAKE_BSIZE);
    	result = parse_archive(&expand, line, nodes, ctxt);
    	return result;
    }
    
    static void
    add_archive_node(Lst nodes, const char *name)
    {
    	GNode *gn;
    
    	gn = Targ_FindNode(name, TARG_CREATE);
    	gn->type |= OP_ARCHV;
    	Lst_AtEnd(nodes, gn);
    }
    
    static bool
    parse_archive(Buffer expand, const char **linePtr, Lst nodeLst, SymTable *ctxt)
    {
    	const char *cp;    	/* Pointer into line */
    	const char *lib;	/* Library-part of specification */
    	const char *elib;
    	const char *member;    	/* Member-part of specification */
    	const char *emember;
    	bool subst_lib;
    
    	/* figure out the library name part */
    	lib = *linePtr;
    	subst_lib = false;
    
    	for (cp = lib; *cp != '(' && *cp != '\0';) {
    		if (*cp == '$') {
    			if (!Var_ParseSkip(&cp, ctxt))
    				return false;
    			subst_lib = true;
    		} else
    			cp++;
    	}
    
    	elib = cp;
    	if (subst_lib) {
    		lib = Var_Substi(lib, elib, ctxt, true);
    		elib = lib + strlen(lib);
    	}
    
    	if (*cp == '\0') {
    		printf("Unclosed parenthesis in archive specification\n");
    		return false;
    	}
    	cp++;
    	/* iterate on members, that may be separated by spaces */
    	for (;;) {
    		/* First skip to the start of the member's name, mark that
    		 * place and skip to the end of it (either white-space or
    		 * a close paren).  */
    		bool subst_member = false;
    
    		while (ISSPACE(*cp))
    			cp++;
    		member = cp;
    		while (*cp != '\0' && *cp != ')' && !ISSPACE(*cp)) {
    			if (*cp == '$') {
    				if (!Var_ParseSkip(&cp, ctxt))
    					return false;
    				subst_member = true;
    			} else
    				cp++;
    		}
    
    		/* If the specification ends without a closing parenthesis,
    		 * chances are there's something wrong (like a missing
    		 * backslash), so it's better to return failure than allow such
    		 * things to happen.  */
    		if (*cp == '\0' || ISSPACE(*cp)) {
    			printf("No closing parenthesis in archive specification\n");
    			return false;
    		}
    
    		/* If we didn't move anywhere, we must be done.  */
    		if (cp == member)
    			break;
    
    		emember = cp;
    
    		/* XXX: This should be taken care of intelligently by
    		 * SuffExpandChildren, both for the archive and the member
    		 * portions.  */
    
    		/* If member contains variables, try and substitute for them.
    		 * This will slow down archive specs with dynamic sources, of
    		 * course, since we'll be (non-)substituting them three times,
    		 * but them's the breaks -- we need to do this since
    		 * SuffExpandChildren calls us, otherwise we could assume the
    		 * thing would be taken care of later.  */
    		if (subst_member) {
    			const char *oldMemberName = member;
    			const char *result;
    
    			member = Var_Substi(member, emember, ctxt, true);
    
    			/* Now form an archive spec and recurse to deal with
    			 * nested variables and multi-word variable values....
    			 * The results are just placed at the end of the
    			 * nodeLst we're returning.  */
    			Buf_Addi(expand, lib, elib);
    			Buf_AddChar(expand, '(');
    			Buf_AddString(expand, member);
    			Buf_AddChar(expand, ')');
    			result = Buf_Retrieve(expand);
    
    			if (strchr(member, '$') &&
    			    memcmp(member, oldMemberName,
    				emember - oldMemberName) == 0) {
    				/* Must contain dynamic sources, so we can't
    				 * deal with it now.  let SuffExpandChildren
    				 * handle it later  */
    				add_archive_node(nodeLst, result);
    			} else if (!Arch_ParseArchive(&result, nodeLst, ctxt))
    				return false;
    			Buf_Reset(expand);
    		} else if (Dir_HasWildcardsi(member, emember)) {
    			LIST  members;
    			char  *m;
    
    			Lst_Init(&members);
    
    			Dir_Expandi(member, emember, defaultPath, &members);
    			while ((m = Lst_DeQueue(&members)) != NULL) {
    				Buf_Addi(expand, lib, elib);
    				Buf_AddChar(expand, '(');
    				Buf_AddString(expand, m);
    				Buf_AddChar(expand, ')');
    				free(m);
    				add_archive_node(nodeLst, Buf_Retrieve(expand));
    				Buf_Reset(expand);
    			}
    		} else {
    			Buf_Addi(expand, lib, elib);
    			Buf_AddChar(expand, '(');
    			Buf_Addi(expand, member, emember);
    			Buf_AddChar(expand, ')');
    			add_archive_node(nodeLst, Buf_Retrieve(expand));
    			Buf_Reset(expand);
    		}
    		if (subst_member)
    			free((char *)member);
    
    	}
    
    	if (subst_lib)
    		free((char *)lib);
    
    	/* We promised the pointer would be set up at the next non-space, so
    	 * we must advance cp there before setting *linePtr... (note that on
    	 * entrance to the loop, cp is guaranteed to point at a ')') */
    	do {
    		cp++;
    	} while (ISSPACE(*cp));
    
    	*linePtr = cp;
    	return true;
    }
    
    /* Helper function: ar fields are not null terminated.	*/
    static long
    field2long(const char *field, size_t length)
    {
    	static char enough[32];
    
    	assert(length < sizeof(enough));
    	memcpy(enough, field, length);
    	enough[length] = '\0';
    	return strtol(enough, NULL, 10);
    }
    
    static Arch *
    read_archive(const char *archive, const char *earchive)
    {
    	FILE *arch;       /* Stream to archive */
    	char magic[SARMAG];
    	Arch *ar;
    	struct SVR4namelist list;
    
    	list.fnametab = NULL;
    
    	/* When we encounter an archive for the first time, we read its
    	 * whole contents, to place it in the cache.  */
    	arch = fopen(archive, "r");
    	if (arch == NULL)
    		return NULL;
    
    	/* Make sure this is an archive we can handle.  */
    	if ((fread(magic, SARMAG, 1, arch) != 1) ||
    	    (strncmp(magic, ARMAG, SARMAG) != 0)) {
    		fclose(arch);
    		return NULL;
    	}
    
    	ar = ohash_create_entry(&arch_info, archive, &earchive);
    	ohash_init(&ar->members, 8, &members_info);
    
    	for (;;) {
    		size_t n;
    		struct ar_hdr arHeader;	/* Archive-member header */
    		off_t size;		/* Size of archive member */
    		char buffer[PATH_MAX];
    		char *memberName; 	/* Current member name while hashing. */
    		char *cp;
    
    		memberName = buffer;
    		n = fread(&arHeader, 1, sizeof(struct ar_hdr), arch);
    
    		/*  Whole archive read ok.  */
    		if (n == 0 && feof(arch)) {
    			free(list.fnametab);
    			fclose(arch);
    			return ar;
    		}
    		if (n < sizeof(struct ar_hdr))
    			break;
    
    		if (memcmp(arHeader.ar_fmag, ARFMAG, sizeof(arHeader.ar_fmag))
    		    != 0) {
    			/* header is bogus.  */
    			break;
    		} else {
    			/* We need to advance the stream's pointer to the start
    			 * of the next header.  Records are padded with
    			 * newlines to an even-byte boundary, so we need to
    			 * extract the size of the record and round it up
    			 * during the seek.  */
    			size = (off_t) field2long(arHeader.ar_size,
    			    sizeof(arHeader.ar_size));
    
    			(void)memcpy(memberName, arHeader.ar_name,
    			    AR_NAME_SIZE);
    			/* Find real end of name (strip extranous ' ')  */
    			for (cp = memberName + AR_NAME_SIZE - 1; *cp == ' ';)
    				cp--;
    			cp[1] = '\0';
    
    #ifdef SVR4ARCHIVES
    			/* SVR4 names are slash terminated.  Also svr4 extended
    			 * AR format.
    			 */
    			if (memberName[0] == '/') {
    				/* SVR4 magic mode.  */
    				memberName = ArchSVR4Entry(&list, memberName,
    				    size, arch);
    				if (memberName == NULL)
    					/* Invalid data */
    					break;
    				else if (memberName == svr4list)
    					/* List of files entry */
    					continue;
    				/* Got the entry.  */
    				/* XXX this assumes further processing, such as
    				 * AR_EFMT1, also applies to SVR4ARCHIVES.  */
    			}
    			else {
    				if (cp[0] == '/')
    					cp[0] = '\0';
    			}
    #endif
    
    #ifdef AR_EFMT1
    			/* BSD 4.4 extended AR format: #1/<namelen>, with name
    			 * as the first <namelen> bytes of the file.  */
    			if (memcmp(memberName, AR_EFMT1, sizeof(AR_EFMT1) - 1)
    			    == 0 && ISDIGIT(memberName[sizeof(AR_EFMT1) - 1])) {
    
    				int elen = atoi(memberName +
    				    sizeof(AR_EFMT1)-1);
    
    				if (elen <= 0 || elen >= PATH_MAX)
    					break;
    				memberName = buffer;
    				if (fread(memberName, elen, 1, arch) != 1)
    					break;
    				memberName[elen] = '\0';
    				if (fseek(arch, -elen, SEEK_CUR) != 0)
    					break;
    				if (DEBUG(ARCH) || DEBUG(MAKE))
    					printf("ArchStat: Extended format entry for %s\n",
    					    memberName);
    			}
    #endif
    
    			ohash_insert(&ar->members,
    			    ohash_qlookup(&ar->members, memberName),
    				new_arch_member(&arHeader, memberName));
    		}
    		if (fseek(arch, (size + 1) & ~1, SEEK_CUR) != 0)
    			break;
    	}
    
    	fclose(arch);
    	ohash_delete(&ar->members);
    	free(list.fnametab);
    	free(ar);
    	return NULL;
    }
    
    /*-
     *-----------------------------------------------------------------------
     * ArchMTimeMember --
     *	Find the modification time of an archive's member, given the
     *	path to the archive and the path to the desired member.
     *
     * Results:
     *	The archive member's modification time, or OUT_OF_DATE if member
     *	was not found (convenient, so that missing members are always
     *	out of date).
     *
     * Side Effects:
     *	Cache the whole archive contents if hash is true.
     *-----------------------------------------------------------------------
     */
    static struct timespec
    ArchMTimeMember(
        const char *archive,	/* Path to the archive */
        const char *member, 	/* Name of member. If it is a path, only the
    				 * last component is used. */
        bool hash)       		/* true if archive should be hashed if not
    				 * already so. */
    {
    	FILE *arch;     	/* Stream to archive */
    	Arch *ar;		/* Archive descriptor */
    	unsigned int slot;	/* Place of archive in the archives hash */
    	const char *end = NULL;
    	const char *cp;
    	struct timespec result;
    
    	ts_set_out_of_date(result);
    	/* Because of space constraints and similar things, files are archived
    	 * using their final path components, not the entire thing, so we need
    	 * to point 'member' to the final component, if there is one, to make
    	 * the comparisons easier...  */
    	cp = strrchr(member, '/');
    	if (cp != NULL)
    		member = cp + 1;
    
    	/* Try to find archive in cache.  */
    	slot = ohash_qlookupi(&archives, archive, &end);
    	ar = ohash_find(&archives, slot);
    
    	/* If not found, get it now.  */
    	if (ar == NULL) {
    		if (!hash) {
    			/* Quick path:  no need to hash the whole archive, just
    			 * use ArchFindMember to get the member's header and
    			 * close the stream again.  */
    			struct ar_hdr arHeader;
    
    			arch = ArchFindMember(archive, member, &arHeader, "r");
    
    			if (arch != NULL) {
    				fclose(arch);
    				ts_set_from_time_t(
    				    (time_t)strtol(arHeader.ar_date, NULL, 10),
    				    result);
    			}
    			return result;
    		}
    		ar = read_archive(archive, end);
    		if (ar != NULL)
    			ohash_insert(&archives, slot, ar);
    	}
    
    	/* If archive was found, get entry we seek.  */
    	if (ar != NULL) {
    		struct arch_member *he;
    		end = NULL;
    
    		he = ohash_find(&ar->members, ohash_qlookupi(&ar->members,
    		    member, &end));
    		if (he != NULL)
    			return mtime_of_member(he);
    		else {
    			if ((size_t)(end - member) > AR_NAME_SIZE) {
    				/* Try truncated name.	*/
    				end = member + AR_NAME_SIZE;
    				he = ohash_find(&ar->members,
    				    ohash_qlookupi(&ar->members, member, &end));
    				if (he != NULL)
    					return mtime_of_member(he);
    			}
    		}
    	}
    	return result;
    }
    
    #ifdef SVR4ARCHIVES
    /*-
     *-----------------------------------------------------------------------
     * ArchSVR4Entry --
     *	Parse an SVR4 style entry that begins with a slash.
     *	If it is "//", then load the table of filenames
     *	If it is "/<offset>", then try to substitute the long file name
     *	from offset of a table previously read.
     *
     * Results:
     *	svr4list: just read a list of names
     *	NULL:	  error occurred
     *	extended name
     *
     * Side-effect:
     *	For a list of names, store the list in l.
     *-----------------------------------------------------------------------
     */
    
    static char *
    ArchSVR4Entry(struct SVR4namelist *l, const char *name, size_t size, FILE *arch)
    {
    #define ARLONGNAMES1 "/"
    #define ARLONGNAMES2 "ARFILENAMES"
    	size_t entry;
    	char *ptr, *eptr;
    
    	assert(name[0] == '/');
    	name++;
    	/* First comes a table of archive names, to be used by subsequent
    	 * calls.  */
    	if (memcmp(name, ARLONGNAMES1, sizeof(ARLONGNAMES1) - 1) == 0 ||
    	    memcmp(name, ARLONGNAMES2, sizeof(ARLONGNAMES2) - 1) == 0) {
    
    		if (l->fnametab != NULL) {
    			if (DEBUG(ARCH))
    				printf("Attempted to redefine an SVR4 name table\n");
    			return NULL;
    		}
    
    		l->fnametab = emalloc(size);
    		l->fnamesize = size;
    
    		if (fread(l->fnametab, size, 1, arch) != 1) {
    			if (DEBUG(ARCH))
    				printf("Reading an SVR4 name table failed\n");
    			return NULL;
    		}
    
    		eptr = l->fnametab + size;
    		for (entry = 0, ptr = l->fnametab; ptr < eptr; ptr++)
    			switch (*ptr) {
    			case '/':
    				entry++;
    				*ptr = '\0';
    				break;
    
    			case '\n':
    				break;
    
    			default:
    				break;
    			}
    		if (DEBUG(ARCH))
    			printf("Found svr4 archive name table with %zu entries\n",
    			    entry);
    		return (char *)svr4list;
    	}
    	/* Then the names themselves are given as offsets in this table.  */
    	if (*name == ' ' || *name == '\0')
    		return NULL;
    
    	entry = (size_t) strtol(name, &eptr, 0);
    	if ((*eptr != ' ' && *eptr != '\0') || eptr == name) {
    		if (DEBUG(ARCH))
    			printf("Could not parse SVR4 name /%s\n", name);
    		return NULL;
    	}
    	if (entry >= l->fnamesize) {
    		if (DEBUG(ARCH))
    			printf("SVR4 entry offset /%s is greater than %zu\n",
    			    name, l->fnamesize);
    		return NULL;
    	}
    
    	if (DEBUG(ARCH))
    		printf("Replaced /%s with %s\n", name, l->fnametab + entry);
    
    	return l->fnametab + entry;
    }
    #endif
    
    
    /*-
     *-----------------------------------------------------------------------
     * ArchFindMember --
     *	Locate a member of an archive, given the path of the archive and
     *	the path of the desired member. If the archive is to be modified,
     *	the mode should be "r+", if not, it should be "r".
     *
     * Results:
     *	A FILE *, opened for reading and writing, positioned right after
     *	the member's header, or NULL if the member was nonexistent.
     *
     * Side Effects:
     *	Fill the struct ar_hdr pointed by arHeaderPtr.
     *-----------------------------------------------------------------------
     */
    static FILE *
    ArchFindMember(
        const char	  *archive,   /* Path to the archive */
        const char	  *member,    /* Name of member. If it is a path, only the
    			       * last component is used. */
        struct ar_hdr *arHeaderPtr,/* Pointer to header structure to be filled in */
        const char	  *mode)      /* mode for opening the stream */
    {
    	FILE *	  arch;       /* Stream to archive */
    	char	  *cp;
    	char	  magic[SARMAG];
    	size_t	  length;
    	struct SVR4namelist list;
    
    	list.fnametab = NULL;
    
    	arch = fopen(archive, mode);
    	if (arch == NULL)
    		return NULL;
    
    	/* Make sure this is an archive we can handle.  */
    	if (fread(magic, SARMAG, 1, arch) != 1 ||
    	    strncmp(magic, ARMAG, SARMAG) != 0) {
    		fclose(arch);
    		return NULL;
    	}
    
    	/* Because of space constraints and similar things, files are archived
    	 * using their final path components, not the entire thing, so we need
    	 * to point 'member' to the final component, if there is one, to make
    	 * the comparisons easier...  */
    	cp = strrchr(member, '/');
    	if (cp != NULL)
    		member = cp + 1;
    
    	length = strlen(member);
    	if (length >= AR_NAME_SIZE)
    		length = AR_NAME_SIZE;
    
    	/* Error handling is simpler than for read_archive, since we just
    	 * look for a given member.  */
    	while (fread(arHeaderPtr, sizeof(struct ar_hdr), 1, arch) == 1) {
    		off_t size;       /* Size of archive member */
    		char *memberName;
    
    		if (memcmp(arHeaderPtr->ar_fmag, ARFMAG,
    		    sizeof(arHeaderPtr->ar_fmag) ) != 0)
    			 /* The header is bogus, so the archive is bad.  */
    			 break;
    
    		memberName = arHeaderPtr->ar_name;
    		if (memcmp(member, memberName, length) == 0) {
    			/* If the member's name doesn't take up the entire
    			 * 'name' field, we have to be careful of matching
    			 * prefixes. Names are space- padded to the right, so
    			 * if the character in 'name' at the end of the matched
    			 * string is anything but a space, this isn't the
    			 * member we sought.  */
    #ifdef SVR4ARCHIVES
    			if (length < sizeof(arHeaderPtr->ar_name) &&
    			    memberName[length] == '/')
    				length++;
    #endif
    			if (length == sizeof(arHeaderPtr->ar_name) ||
    			    memberName[length] == ' ') {
    				free(list.fnametab);
    				return arch;
    			}
    		}
    
    		size = (off_t) field2long(arHeaderPtr->ar_size,
    		    sizeof(arHeaderPtr->ar_size));
    
    #ifdef SVR4ARCHIVES
    		/* svr4 names are slash terminated. Also svr4 extended AR
    		 * format.
    		 */
    		if (memberName[0] == '/') {
    			/* svr4 magic mode.  */
    			memberName = ArchSVR4Entry(&list, arHeaderPtr->ar_name,
    			    size, arch);
    			if (memberName == NULL)
    				/* Invalid data */
    				break;
    			else if (memberName == svr4list)
    				/* List of files entry */
    				continue;
    			/* Got the entry.  */
    			if (strcmp(memberName, member) == 0) {
    				free(list.fnametab);
    				return arch;
    			}
    		}
    #endif
    
    #ifdef AR_EFMT1
    		/* BSD 4.4 extended AR format: #1/<namelen>, with name as the
    		 * first <namelen> bytes of the file.  */
    		if (memcmp(memberName, AR_EFMT1, sizeof(AR_EFMT1) - 1) == 0 &&
    		    ISDIGIT(memberName[sizeof(AR_EFMT1) - 1])) {
    			char ename[PATH_MAX];
    
    			int elength = atoi(memberName + sizeof(AR_EFMT1)-1);
    
    			if (elength <= 0 || elength >= PATH_MAX)
    				break;
    			if (fread(ename, elength, 1, arch) != 1)
    				break;
    			if (fseek(arch, -elength, SEEK_CUR) != 0)
    				break;
    			ename[elength] = '\0';
    			if (DEBUG(ARCH) || DEBUG(MAKE))
    				printf("ArchFind: Extended format entry for %s\n", ename);
    			/* Found as extended name.	*/
    			if (strcmp(ename, member) == 0) {
    				free(list.fnametab);
    				return arch;
    			}
    		}
    #endif
    		/* This isn't the member we're after, so we need to advance the
    		 * stream's pointer to the start of the next header.  */
    		if (fseek(arch, (size + 1) & ~1, SEEK_CUR) != 0)
    			break;
    	}
    
    	/* We did not find the member, or we ran into an error while reading
    	 * the archive.  */
    #ifdef SVRARCHIVES
    	free(list.fnametab);
    #endif
    	fclose(arch);
    	return NULL;
    }
    
    static void
    ArchTouch(const char *archive, const char *member)
    {
    	FILE *arch;
    	struct ar_hdr arHeader;
    
    	arch = ArchFindMember(archive, member, &arHeader, "r+");
    	if (arch != NULL) {
    		snprintf(arHeader.ar_date, sizeof(arHeader.ar_date),
    		    "%-12ld", (long) time(NULL));
    		if (fseek(arch, -sizeof(struct ar_hdr), SEEK_CUR) == 0)
    			(void)fwrite(&arHeader, sizeof(struct ar_hdr), 1, arch);
    		fclose(arch);
    	}
    }
    
    /*
     * Side Effects:
     *	The modification time of the entire archive is also changed.
     *	For a library, this could necessitate the re-ranlib'ing of the
     *	whole thing.
     */
    void
    Arch_Touch(GNode *gn)
    {
    	ArchTouch(Var(ARCHIVE_INDEX, gn), Var(MEMBER_INDEX, gn));
    }
    
    struct timespec
    Arch_MTime(GNode *gn)
    {
    	gn->mtime = ArchMTimeMember(Var(ARCHIVE_INDEX, gn),
    	     Var(MEMBER_INDEX, gn), true);
    
    	return gn->mtime;
    }
    
    struct timespec
    Arch_MemMTime(GNode *gn)
    {
    	LstNode ln;
    
    	for (ln = Lst_First(&gn->parents); ln != NULL; ln = Lst_Adv(ln)) {
    		GNode *pgn;
    		char *nameStart;
    		char *nameEnd;
    
    		pgn = Lst_Datum(ln);
    
    		if (pgn->type & OP_ARCHV) {
    			/* If the parent is an archive specification and is
    			 * being built and its member's name matches the name of
    			 * the node we were given, record the modification time
    			 * of the parent in the child. We keep searching its
    			 * parents in case some other parent requires this
    			 * child to exist...  */
    			if ((nameStart = strchr(pgn->name, '(') ) != NULL) {
    				nameStart++;
    				nameEnd = strchr(nameStart, ')');
    			} else
    				nameEnd = NULL;
    
    			if (pgn->must_make && nameEnd != NULL &&
    			    strncmp(nameStart, gn->name, nameEnd - nameStart)
    			    == 0 && gn->name[nameEnd-nameStart] == '\0')
    				gn->mtime = Arch_MTime(pgn);
    		} else if (pgn->must_make) {
    			/* Something which isn't a library depends on the
    			 * existence of this target, so it needs to exist.  */
    			ts_set_out_of_date(gn->mtime);
    			break;
    		}
    	}
    	return gn->mtime;
    }
    
    void
    Arch_Init(void)
    {
    	ohash_init(&archives, 4, &arch_info);
    }