Russ, this code works with the files that jmk sent me, which
appear to be in the same format as those spit out by vl -H5.
It is a major departure from how the code used to work, though.
Previously it would load up elf sections by name using the
SHDRs and string table.  The vl -H5 files and the files jmk sent
me do not have this information.  So the result is libmach can
load up the vl -H5 files with this patch, but probably can no
longer load up some elf files that it previously was capable of
loading.
If you would prefer keeping the old functionality rather than the
vl ELF file support, I can fix up the endian issues if someone
provides me with the appropriate Irix elf files to test against.

Notes:
Thu Feb 3 10:33:26 EST 2005 rsc
    I agree that the right thing to do is use
    the phdr info instead of the shdr.  The shdr
    is only there as a courtesy, while the phdr
    is required for the binary to be loaded by the OS.
    However, I'd prefer not to use constant offsets
    into the phdr.  There are type bits in the phdr that
    can be used to figure out which section is the 
    text, which is the data, and which is the symbols.
    See http://cvs.pdos.lcs.mit.edu/cvs/plan9/src/libmach/elf.c?rev=HEAD
    for how I parse the ELF files from Linux and FreeBSD.
    
    Russ


Reference: /n/sources/patch/sorry/libmach-elf
Date: Sat Feb  5 14:30:04 CET 2005
Reviewed-by: rsc

--- /sys/src/libmach/executable.c	Sat Feb  5 14:30:03 2005
+++ /sys/src/libmach/executable.c	Sat Feb  5 14:30:03 2005
@@ -438,24 +438,7 @@
 	return 1;
 }
 
-static Shdr*
-elfsectbyname(int fd, Ehdr *hp, Shdr *sp, char *name)
-{
-	int i, offset, n;
-	char s[64];
 
-	offset = sp[hp->shstrndx].offset;
-	for(i = 1; i < hp->shnum; i++) {
-		seek(fd, offset+sp[i].name, 0);
-		n = read(fd, s, sizeof(s)-1);
-		if(n < 0)
-			continue;
-		s[n] = 0;
-		if(strcmp(s, name) == 0)
-			return &sp[i]; 
-	}
-	return 0;
-}
 /*
  *	Decode an Irix 5.x ELF header
  */
@@ -464,96 +447,49 @@
 {
 
 	Ehdr *ep;
-	Shdr *es, *txt, *init, *s;
-	long addr, size, offset, bsize;
+	Phdr ph[3];
 
+	/* undo the previous incorrect swap and redo it properly */
 	ep = &hp->e;
-	if(ep->type != 8 || ep->machine != 2 || ep->version != 1)
+	hswal((long*)ep, sizeof *ep / sizeof(long), beswal);
+	ep->type = beswab(ep->type);
+	ep->machine = beswab(ep->machine);
+	ep->version = beswal(ep->version);
+	ep->elfentry = beswal(ep->elfentry);
+	ep->phoff = beswal(ep->phoff);
+	ep->shoff = beswal(ep->shoff);
+	ep->flags = beswal(ep->flags);
+	ep->ehsize = beswab(ep->ehsize);
+	ep->phentsize = beswab(ep->phentsize);
+	ep->phnum = beswab(ep->phnum);
+	ep->shentsize = beswab(ep->shentsize);
+	ep->shnum = beswab(ep->shnum);
+	ep->shstrndx = beswab(ep->shstrndx);
+	if(ep->type != 2 || ep->machine != 8 || ep->version != 1)
 		return 0;
 
 	fp->magic = ELF_MAG;
 	fp->hdrsz = (ep->ehsize+ep->phnum*ep->phentsize+16)&~15;
 
-	if(ep->shnum <= 0) {
-		werrstr("no ELF header sections");
+	if(ep->phnum != 3) {
+		werrstr("unexpected ELF headers");
 		return 0;
 	}
-	es = malloc(sizeof(Shdr)*ep->shnum);
-	if(es == 0)
-		return 0;
 
-	seek(fd, ep->shoff, 0);
-	if(read(fd, es, sizeof(Shdr)*ep->shnum) < 0){
-		free(es);
+	seek(fd, ep->phoff, 0);
+	if(read(fd, ph, sizeof(Phdr)*ep->phnum) < 0)
 		return 0;
-	}
-
-	txt = elfsectbyname(fd, ep, es, ".text");
-	init = elfsectbyname(fd, ep, es, ".init");
-	if(txt == 0 || init == 0 || init != txt+1)
-		goto bad;
-	if(txt->addr+txt->size != init->addr)
-		goto bad;
-	settext(fp, ep->elfentry, txt->addr, txt->size+init->size, txt->offset);
-
-	addr = 0;
-	offset = 0;
-	size = 0;
-	s = elfsectbyname(fd, ep, es, ".data");
-	if(s) {
-		addr = s->addr;
-		size = s->size;
-		offset = s->offset;
-	}
+	hswal((long*)ph, sizeof(Phdr)*ep->phnum/sizeof(long), beswal);
 
-	s = elfsectbyname(fd, ep, es, ".rodata");
-	if(s) {
-		if(addr){
-			if(addr+size != s->addr)
-				goto bad;
-		} else {
-			addr = s->addr;
-			offset = s->offset;
-		}
-		size += s->size;
-	}
-
-	s = elfsectbyname(fd, ep, es, ".got");
-	if(s) {
-		if(addr){
-			if(addr+size != s->addr)
-				goto bad;
-		} else {
-			addr = s->addr;
-			offset = s->offset;
-		}
-		size += s->size;
-	}
-
-	bsize = 0;
-	s = elfsectbyname(fd, ep, es, ".bss");
-	if(s) {
-		if(addr){
-			if(addr+size != s->addr)
-				goto bad;
-		} else {
-			addr = s->addr;
-			offset = s->offset;
-		}
-		bsize = s->size;
+	if(ph[0].type != LOAD || ph[1].type != LOAD || ph[2].type != NOPTYPE) {
+		werrstr("unexpected ELF headers");
+		return 0;
 	}
 
-	if(addr == 0)
-		goto bad;
-
-	setdata(fp, addr, size, offset, bsize);
-	fp->name = "IRIX Elf a.out executable";
-	free(es);
+	settext(fp, ep->elfentry, ph[0].vaddr, ph[0].memsz, ph[0].offset);
+	setdata(fp, ph[1].vaddr, ph[1].memsz, ph[1].offset, ph[1].memsz - ph[1].filesz);
+	setsym(fp, ph[2].filesz, 0, ph[2].memsz, ph[2].offset);
 	return 1;
-bad:
-	free(es);
-	werrstr("ELF sections scrambled");
-	return 0;
 }
 
 /*