psymtab.c

Sun Solaris 10 中的 DTrace 组件的源代码。请参看: http://www.sun.com/software/solaris/observability.jsp

 */
static int
file_differs(struct ps_prochandle *P, Elf *elf, file_info_t *fptr)
{
	Elf_Scn *scn;
	GElf_Shdr shdr;
	GElf_Dyn dyn;
	Elf_Data *data;
	uint_t i, ndyn;
	GElf_Xword cksum;
	uintptr_t addr;

	if (fptr->file_map == NULL)
		return (0);

	if ((Pcontent(P) & (CC_CONTENT_TEXT | CC_CONTENT_DATA)) !=
	    (CC_CONTENT_TEXT | CC_CONTENT_DATA))
		return (0);

	/*
	 * First, we find the checksum value in the elf file.
	 */
	scn = NULL;
	while ((scn = elf_nextscn(elf, scn)) != NULL) {
		if (gelf_getshdr(scn, &shdr) != NULL &&
		    shdr.sh_type == SHT_DYNAMIC)
			goto found_shdr;
	}
	return (0);

found_shdr:
	if ((data = elf_getdata(scn, NULL)) == NULL)
		return (0);

	if (P->status.pr_dmodel == PR_MODEL_ILP32)
		ndyn = shdr.sh_size / sizeof (Elf32_Dyn);
#ifdef _LP64
	else if (P->status.pr_dmodel == PR_MODEL_LP64)
		ndyn = shdr.sh_size / sizeof (Elf64_Dyn);
#endif
	else
		return (0);

	for (i = 0; i < ndyn; i++) {
		if (gelf_getdyn(data, i, &dyn) != NULL &&
		    dyn.d_tag == DT_CHECKSUM)
			goto found_cksum;
	}
	return (0);

found_cksum:
	cksum = dyn.d_un.d_val;
	dprintf("elf cksum value is %llx\n", (u_longlong_t)cksum);

	/*
	 * Get the base of the text mapping that corresponds to this file.
	 */
	addr = fptr->file_map->map_pmap.pr_vaddr;

	if (P->status.pr_dmodel == PR_MODEL_ILP32) {
		Elf32_Ehdr ehdr;
		Elf32_Phdr phdr;
		Elf32_Dyn dync, *dynp;
		uint_t i;

		if (read_ehdr32(P, &ehdr, addr) != 0 ||
		    read_dynamic_phdr32(P, &ehdr, &phdr, addr) != 0)
			return (0);

		if (ehdr.e_type == ET_DYN)
			phdr.p_vaddr += addr;
		if ((dynp = malloc(phdr.p_filesz)) == NULL)
			return (0);
		dync.d_tag = DT_NULL;
		if (Pread(P, dynp, phdr.p_filesz, phdr.p_vaddr) !=
		    phdr.p_filesz) {
			free(dynp);
			return (0);
		}

		for (i = 0; i < phdr.p_filesz / sizeof (Elf32_Dyn); i++) {
			if (dynp[i].d_tag == DT_CHECKSUM)
				dync = dynp[i];
		}

		free(dynp);

		if (dync.d_tag != DT_CHECKSUM)
			return (0);

		dprintf("image cksum value is %llx\n",
		    (u_longlong_t)dync.d_un.d_val);
		return (dync.d_un.d_val != cksum);
#ifdef _LP64
	} else if (P->status.pr_dmodel == PR_MODEL_LP64) {
		Elf64_Ehdr ehdr;
		Elf64_Phdr phdr;
		Elf64_Dyn dync, *dynp;
		uint_t i;

		if (read_ehdr64(P, &ehdr, addr) != 0 ||
		    read_dynamic_phdr64(P, &ehdr, &phdr, addr) != 0)
			return (0);

		if (ehdr.e_type == ET_DYN)
			phdr.p_vaddr += addr;
		if ((dynp = malloc(phdr.p_filesz)) == NULL)
			return (0);
		dync.d_tag = DT_NULL;
		if (Pread(P, dynp, phdr.p_filesz, phdr.p_vaddr) !=
		    phdr.p_filesz) {
			free(dynp);
			return (0);
		}

		for (i = 0; i < phdr.p_filesz / sizeof (Elf64_Dyn); i++) {
			if (dynp[i].d_tag == DT_CHECKSUM)
				dync = dynp[i];
		}

		free(dynp);

		if (dync.d_tag != DT_CHECKSUM)
			return (0);

		dprintf("image cksum value is %llx\n",
		    (u_longlong_t)dync.d_un.d_val);
		return (dync.d_un.d_val != cksum);
#endif	/* _LP64 */
	}

	return (0);
}

static Elf *
fake_elf(struct ps_prochandle *P, file_info_t *fptr)
{
	enum {
		DI_PLTGOT = 0,
		DI_JMPREL,
		DI_PLTRELSZ,
		DI_PLTREL,
		DI_SYMTAB,
		DI_HASH,
		DI_SYMENT,
		DI_STRTAB,
		DI_STRSZ,
		DI_NENT
	};
	uintptr_t addr;
	size_t size = 0;
	caddr_t elfdata = NULL;
	Elf *elf;
	Elf32_Word nchain;
	static char shstr[] = ".shstrtab\0.dynsym\0.dynstr\0.dynamic\0.plt";

	if (fptr->file_map == NULL)
		return (NULL);

	if ((Pcontent(P) & (CC_CONTENT_TEXT | CC_CONTENT_DATA)) !=
	    (CC_CONTENT_TEXT | CC_CONTENT_DATA))
		return (NULL);

	addr = fptr->file_map->map_pmap.pr_vaddr;

	/*
	 * We're building a in memory elf file that will let us use libelf
	 * for most of the work we need to later (e.g. symbol table lookups).
	 * We need sections for the dynsym, dynstr, and plt, and we need
	 * the program headers from the text section. The former is used in
	 * Pbuild_file_symtab(); the latter is used in several functions in
	 * Pcore.c to reconstruct the origin of each mapping from the load
	 * object that spawned it.
	 *
	 * Here are some useful pieces of elf trivia that will help
	 * to elucidate this code.
	 *
	 * All the information we need about the dynstr can be found in these
	 * two entries in the dynamic section:
	 *
	 *	DT_STRTAB	base of dynstr
	 *	DT_STRSZ	size of dynstr
	 *
	 * So deciphering the dynstr is pretty straightforward.
	 *
	 * The dynsym is a little trickier.
	 *
	 *	DT_SYMTAB	base of dynsym
	 *	DT_SYMENT	size of a dynstr entry (Elf{32,64}_Sym)
	 *	DT_HASH		base of hash table for dynamic lookups
	 *
	 * The DT_SYMTAB entry gives us any easy way of getting to the base
	 * of the dynsym, but getting the size involves rooting around in the
	 * dynamic lookup hash table. Here's the layout of the hash table:
	 *
	 *		+-------------------+
	 *		|	nbucket	    |	All values are of type
	 *		+-------------------+	Elf32_Word
	 *		|	nchain	    |
	 *		+-------------------+
	 *		|	bucket[0]   |
	 *		|	. . .	    |
	 *		| bucket[nbucket-1] |
	 *		+-------------------+
	 *		|	chain[0]    |
	 *		|	. . .	    |
	 *		|  chain[nchain-1]  |
	 *		+-------------------+
	 *	(figure 5-12 from the SYS V Generic ABI)
	 *
	 * Symbols names are hashed into a particular bucket which contains
	 * an index into the symbol table. Each entry in the symbol table
	 * has a corresponding entry in the chain table which tells the
	 * consumer where the next entry in the hash chain is. We can use
	 * the nchain field to find out the size of the dynsym.
	 *
	 * We can figure out the size of the .plt section, but it takes some
	 * doing. We need to use the following information:
	 *
	 *	DT_PLTGOT	base of the PLT
	 *	DT_JMPREL	base of the PLT's relocation section
	 *	DT_PLTRELSZ	size of the PLT's relocation section
	 *	DT_PLTREL	type of the PLT's relocation section
	 *
	 * We can use the relocation section to figure out the address of the
	 * last entry and subtract off the value of DT_PLTGOT to calculate
	 * the size of the PLT.
	 *
	 * For more information, check out the System V Generic ABI.
	 */

	if (P->status.pr_dmodel == PR_MODEL_ILP32) {
		Elf32_Ehdr ehdr, *ep;
		Elf32_Phdr phdr;
		Elf32_Shdr *sp;
		Elf32_Dyn *dp;
		Elf32_Dyn *d[DI_NENT] = { 0 };
		uint_t i, dcount = 0;
		uint32_t off;
		size_t pltsz = 0, pltentsz;

		if (read_ehdr32(P, &ehdr, addr) != 0 ||
		    read_dynamic_phdr32(P, &ehdr, &phdr, addr) != 0)
			return (NULL);

		if (ehdr.e_type == ET_DYN)
			phdr.p_vaddr += addr;

		if ((dp = malloc(phdr.p_filesz)) == NULL)
			return (NULL);

		if (Pread(P, dp, phdr.p_filesz, phdr.p_vaddr) !=
		    phdr.p_filesz) {
			free(dp);
			return (NULL);
		}

		for (i = 0; i < phdr.p_filesz / sizeof (Elf32_Dyn); i++) {
			switch (dp[i].d_tag) {
			/*
			 * For the .plt section.
			 */
			case DT_PLTGOT:
				d[DI_PLTGOT] = &dp[i];
				continue;
			case DT_JMPREL:
				d[DI_JMPREL] = &dp[i];
				continue;
			case DT_PLTRELSZ:
				d[DI_PLTRELSZ] = &dp[i];
				continue;
			case DT_PLTREL:
				d[DI_PLTREL] = &dp[i];
				continue;
			default:
				continue;

			/*
			 * For the .dynsym section.
			 */
			case DT_SYMTAB:
				d[DI_SYMTAB] = &dp[i];
				break;
			case DT_HASH:
				d[DI_HASH] = &dp[i];
				break;
			case DT_SYMENT:
				d[DI_SYMENT] = &dp[i];
				break;

			/*
			 * For the .dynstr section.
			 */
			case DT_STRTAB:
				d[DI_STRTAB] = &dp[i];
				break;
			case DT_STRSZ:
				d[DI_STRSZ] = &dp[i];
				break;
			}

			dcount++;
		}

		/*
		 * We need all of those dynamic entries in order to put
		 * together a complete set of elf sections, but we'll
		 * let the PLT section slide if need be. The dynsym- and
		 * dynstr-related dynamic entries are mandatory in both
		 * executables and shared objects so if one of those is
		 * missing, we're in some trouble and should abort.
		 */
		if (dcount + 4 != DI_NENT) {
			dprintf("text section missing required dynamic "
			    "entries\n");
			return (NULL);
		}

		if (ehdr.e_type == ET_DYN) {
			if (d[DI_PLTGOT] != NULL)
				d[DI_PLTGOT]->d_un.d_ptr += addr;
			if (d[DI_JMPREL] != NULL)
				d[DI_JMPREL]->d_un.d_ptr += addr;
			d[DI_SYMTAB]->d_un.d_ptr += addr;
			d[DI_HASH]->d_un.d_ptr += addr;
			d[DI_STRTAB]->d_un.d_ptr += addr;
		}

		/* elf header */
		size = sizeof (Elf32_Ehdr);

		/* program headers from in-core elf fragment */
		size += ehdr.e_phnum * ehdr.e_phentsize;

		/* unused shdr, and .shstrtab section */
		size += sizeof (Elf32_Shdr);
		size += sizeof (Elf32_Shdr);
		size += roundup(sizeof (shstr), 4);

		/* .dynsym section */
		size += sizeof (Elf32_Shdr);
		if (Pread(P, &nchain, sizeof (nchain),
		    d[DI_HASH]->d_un.d_ptr + 4) != sizeof (nchain))
			goto bad32;
		size += sizeof (Elf32_Sym) * nchain;

		/* .dynstr section */
		size += sizeof (Elf32_Shdr);
		size += roundup(d[DI_STRSZ]->d_un.d_val, 4);

		/* .dynamic section */
		size += sizeof (Elf32_Shdr);
		size += roundup(phdr.p_filesz, 4);

		/* .plt section */
		if (d[DI_PLTGOT] != NULL && d[DI_JMPREL] != NULL &&
		    d[DI_PLTRELSZ] != NULL && d[DI_PLTREL] != NULL) {
			uintptr_t penult, ult;
			uintptr_t jmprel = d[DI_JMPREL]->d_un.d_ptr;
			size_t pltrelsz = d[DI_PLTRELSZ]->d_un.d_val;

			if (d[DI_PLTREL]->d_un.d_val == DT_RELA) {
				uint_t ndx = pltrelsz / sizeof (Elf32_Rela) - 2;
				Elf32_Rela r[2];

				if (Pread(P, r, sizeof (r), jmprel +
				    sizeof (r[0]) * ndx) != sizeof (r))
					goto bad32;

				penult = r[0].r_offset;
				ult = r[1].r_offset;

			} else if (d[DI_PLTREL]->d_un.d_val == DT_REL) {
				uint_t ndx = pltrelsz / sizeof (Elf32_Rel) - 2;
				Elf32_Rel r[2];

				if (Pread(P, r, sizeof (r), jmprel +
				    sizeof (r[0]) * ndx) != sizeof (r))
					goto bad32;

				penult = r[0].r_offset;
				ult = r[1].r_offset;
			} else {
				goto bad32;
			}

			pltentsz = ult - penult;

			if (ehdr.e_type == ET_DYN)
				ult += addr;

			pltsz = ult - d[DI_PLTGOT]->d_un.d_ptr + pltentsz;

			size += sizeof (Elf32_Shdr);
			size += roundup(pltsz, 4);
		}

		if ((elfdata = calloc(1, size)) == NULL)
			goto bad32;

		/* LINTED - alignment */
		ep = (Elf32_Ehdr *)elfdata;
		(void) memcpy(ep, &ehdr, offsetof(Elf32_Ehdr, e_phoff));

		ep->e_ehsize = sizeof (Elf32_Ehdr);
		ep->e_phoff = sizeof (Elf32_Ehdr);
		ep->e_phentsize = ehdr.e_phentsize;
		ep->e_phnum = ehdr.e_phnum;
		ep->e_shoff = ep->e_phoff + ep->e_phnum * ep->e_phentsize;
		ep->e_shentsize = sizeof (Elf32_Shdr);
		ep->e_shnum = (pltsz == 0) ? 5 : 6;
		ep->e_shstrndx = 1;

		/* LINTED - alignment */
		sp = (Elf32_Shdr *)(elfdata + ep->e_shoff);
		off = ep->e_shoff + ep->e_shentsize * ep->e_shnum;

		/*
		 * Copying the program headers directly from the process's
		 * address space is a little suspect, but since we only
		 * use them for their address and size values, this is fine.
		 */
		if (Pread(P, &elfdata[ep->e_phoff],
		    ep->e_phnum * ep->e_phentsize, addr + ehdr.e_phoff) !=
		    ep->e_phnum * ep->e_phentsize) {
			free(elfdata);
			goto bad32;
		}

		/*
		 * The first elf section is always skipped.
		 */
		sp++;

		/*
		 * Section Header[1]  sh_name: .shstrtab
		 */
		sp->sh_name = 0;
		sp->sh_type = SHT_STRTAB;
		sp->sh_flags = SHF_STRINGS;
		sp->sh_addr = 0;
		sp->sh_offset = off;
		sp->sh_size = sizeof (shstr);
		sp->sh_link = 0;
		sp->sh_info = 0;
		sp->sh_addralign = 1;
		sp->sh_entsize = 0;

		(void) memcpy(&elfdata[off], shstr, sizeof (shstr));
		off += roundup(sp->sh_size, 4);
		sp++;

		/*
		 * Section Header[2]  sh_name: .dynsym
		 */
		sp->sh_name = 10;
		sp->sh_type = SHT_DYNSYM;
		sp->sh_flags = SHF_ALLOC;
		sp->sh_addr = d[DI_SYMTAB]->d_un.d_ptr;
		if (ehdr.e_type == ET_DYN)
			sp->sh_addr -= addr;
		sp->sh_offset = off;
		sp->sh_size = nchain * sizeof (Elf32_Sym);
		sp->sh_link = 3;
		sp->sh_info = 1;
		sp->sh_addralign = 4;
		sp->sh_entsize = sizeof (Elf32_Sym);

		if (Pread(P, &elfdata[off], sp->sh_size,
		    d[DI_SYMTAB]->d_un.d_ptr) != sp->sh_size) {
			free(elfdata);
			goto bad32;
		}

		off += roundup(sp->sh_size, 4);
		sp++;

		/*
		 * Section Header[3]  sh_name: .dynstr
		 */
		sp->sh_name = 18;
		sp->sh_type = SHT_STRTAB;
		sp->sh_flags = SHF_ALLOC | SHF_STRINGS;
		sp->sh_addr = d[DI_STRTAB]->d_un.d_ptr;
		if (ehdr.e_type == ET_DYN)
			sp->sh_addr -= addr;
		sp->sh_offset = off;
		sp->sh_size = d[DI_STRSZ]->d_un.d_val;
		sp->sh_link = 0;
		sp->sh_info = 0;
		sp->sh_addralign = 1;
		sp->sh_entsize = 0;

		if (Pread(P, &elfdata[off], sp->sh_size,
		    d[DI_STRTAB]->d_un.d_ptr) != sp->sh_size) {
			free(elfdata);
			goto bad32;
		}
		off += roundup(sp->sh_size, 4);
		sp++;

		/*
		 * Section Header[4]  sh_name: .dynamic
		 */
		sp->sh_name = 26;
		sp->sh_type = SHT_DYNAMIC;
		sp->sh_flags = SHF_WRITE | SHF_ALLOC;
		sp->sh_addr = phdr.p_vaddr;
		if (ehdr.e_type == ET_DYN)
			sp->sh_addr -= addr;
		sp->sh_offset = off;
		sp->sh_size = phdr.p_filesz;
		sp->sh_link = 3;
		sp->sh_info = 0;
		sp->sh_addralign = 4;