add general fdpic support in dynamic linker and arch support for sh

at this point not all functionality is complete. the dynamic linker
itself, and main app if it is also loaded by the kernel, take
advantage of fdpic and do not need constant displacement between
segments, but additional libraries loaded by the dynamic linker follow
normal ELF semantics for mapping still. this fully works, but does not
admit shared text on nommu.

in terms of actual functional correctness, dlsym's results are
presently incorrect for function symbols, RTLD_NEXT fails to identify
the caller correctly, and dladdr fails almost entirely.

with the dynamic linker entry point working, support for static pie is
automatically included, but linking the main application as ET_DYN
(pie) probably does not make sense for fdpic anyway. ET_EXEC is
equally relocatable but more efficient at representing relocations.

3 files changed, 202 insertions, 14 deletions

diff --git a/src/internal/dynlink.h b/src/internal/dynlink.h
index 369f183e..b9333926 100644
--- a/src/internal/dynlink.h
+++ b/src/internal/dynlink.h
@@ -49,16 +49,27 @@ struct fdpic_loadmap {
 	struct fdpic_loadseg segs[];
 };
 
+struct fdpic_dummy_loadmap {
+	unsigned short version, nsegs;
+	struct fdpic_loadseg segs[1];
+};
+
 #include "reloc.h"
 
-#define IS_RELATIVE(x) ( \
+#ifndef DL_FDPIC
+#define DL_FDPIC 0
+#endif
+
+#if !DL_FDPIC
+#define IS_RELATIVE(x,s) ( \
 	(R_TYPE(x) == REL_RELATIVE) || \
 	(R_TYPE(x) == REL_SYM_OR_REL && !R_SYM(x)) )
-
-#define IS_FDPIC_RELATIVE(x,s) ( ( \
+#else
+#define IS_RELATIVE(x,s) ( ( \
 	(R_TYPE(x) == REL_FUNCDESC_VAL) || \
 	(R_TYPE(x) == REL_SYMBOLIC) ) \
 	&& (((s)[R_SYM(x)].st_info & 0xf) == STT_SECTION) )
+#endif
 
 #ifndef NEED_MIPS_GOT_RELOCS
 #define NEED_MIPS_GOT_RELOCS 0
diff --git a/src/ldso/dlstart.c b/src/ldso/dlstart.c
index e84e073e..46f50114 100644
--- a/src/ldso/dlstart.c
+++ b/src/ldso/dlstart.c
@@ -33,10 +33,70 @@ void _dlstart_c(size_t *sp, size_t *dynv)
 	for (i=0; auxv[i]; i+=2) if (auxv[i]<AUX_CNT)
 		aux[auxv[i]] = auxv[i+1];
 
+#if DL_FDPIC
+	struct fdpic_loadseg *segs, fakeseg;
+	size_t j;
+	if (dynv) {
+		/* crt_arch.h entry point asm is responsible for reserving
+		 * space and moving the extra fdpic arguments to the stack
+		 * vector where they are easily accessible from C. */
+		segs = ((struct fdpic_loadmap *)(sp[-1] ? sp[-1] : sp[-2]))->segs;
+	} else {
+		/* If dynv is null, the entry point was started from loader
+		 * that is not fdpic-aware. We can assume normal fixed-
+		 * displacement ELF loading was performed, but when ldso was
+		 * run as a command, finding the Ehdr is a heursitic: we
+		 * have to assume Phdrs start in the first 4k of the file. */
+		base = aux[AT_BASE];
+		if (!base) base = aux[AT_PHDR] & -4096;
+		segs = &fakeseg;
+		segs[0].addr = base;
+		segs[0].p_vaddr = 0;
+		segs[0].p_memsz = -1;
+		Ehdr *eh = (void *)base;
+		Phdr *ph = (void *)(base + eh->e_phoff);
+		size_t phnum = eh->e_phnum;
+		size_t phent = eh->e_phentsize;
+		while (phnum-- && ph->p_type != PT_DYNAMIC)
+			ph = (void *)((size_t)ph + phent);
+		dynv = (void *)(base + ph->p_vaddr);
+	}
+#endif
+
 	for (i=0; i<DYN_CNT; i++) dyn[i] = 0;
 	for (i=0; dynv[i]; i+=2) if (dynv[i]<DYN_CNT)
 		dyn[dynv[i]] = dynv[i+1];
 
+#if DL_FDPIC
+	for (i=0; i<DYN_CNT; i++) {
+		if (i==DT_RELASZ || i==DT_RELSZ) continue;
+		if (!dyn[i]) continue;
+		for (j=0; dyn[i]-segs[j].p_vaddr >= segs[j].p_memsz; j++);
+		dyn[i] += segs[j].addr - segs[j].p_vaddr;
+	}
+	base = 0;
+
+	const Sym *syms = (void *)dyn[DT_SYMTAB];
+
+	rel = (void *)dyn[DT_RELA];
+	rel_size = dyn[DT_RELASZ];
+	for (; rel_size; rel+=3, rel_size-=3*sizeof(size_t)) {
+		if (!IS_RELATIVE(rel[1], syms)) continue;
+		for (j=0; rel[0]-segs[j].p_vaddr >= segs[j].p_memsz; j++);
+		size_t *rel_addr = (void *)
+			(rel[0] + segs[j].addr - segs[j].p_vaddr);
+		if (R_TYPE(rel[1]) == REL_FUNCDESC_VAL) {
+			*rel_addr += segs[rel_addr[1]].addr
+				- segs[rel_addr[1]].p_vaddr
+				+ syms[R_SYM(rel[1])].st_value;
+			rel_addr[1] = dyn[DT_PLTGOT];
+		} else {
+			size_t val = syms[R_SYM(rel[1])].st_value;
+			for (j=0; val-segs[j].p_vaddr >= segs[j].p_memsz; j++);
+			*rel_addr = rel[2] + segs[j].addr - segs[j].p_vaddr + val;
+		}
+	}
+#else
 	/* If the dynamic linker is invoked as a command, its load
 	 * address is not available in the aux vector. Instead, compute
 	 * the load address as the difference between &_DYNAMIC and the
@@ -68,7 +128,7 @@ void _dlstart_c(size_t *sp, size_t *dynv)
 	rel = (void *)(base+dyn[DT_REL]);
 	rel_size = dyn[DT_RELSZ];
 	for (; rel_size; rel+=2, rel_size-=2*sizeof(size_t)) {
-		if (!IS_RELATIVE(rel[1])) continue;
+		if (!IS_RELATIVE(rel[1], 0)) continue;
 		size_t *rel_addr = (void *)(base + rel[0]);
 		*rel_addr += base;
 	}
@@ -76,10 +136,11 @@ void _dlstart_c(size_t *sp, size_t *dynv)
 	rel = (void *)(base+dyn[DT_RELA]);
 	rel_size = dyn[DT_RELASZ];
 	for (; rel_size; rel+=3, rel_size-=3*sizeof(size_t)) {
-		if (!IS_RELATIVE(rel[1])) continue;
+		if (!IS_RELATIVE(rel[1], 0)) continue;
 		size_t *rel_addr = (void *)(base + rel[0]);
 		*rel_addr = base + rel[2];
 	}
+#endif
 
 	stage2_func dls2;
 	GETFUNCSYM(&dls2, __dls2, base+dyn[DT_PLTGOT]);
diff --git a/src/ldso/dynlink.c b/src/ldso/dynlink.c
index 4b52a5a6..4903dbd2 100644
--- a/src/ldso/dynlink.c
+++ b/src/ldso/dynlink.c
@@ -42,7 +42,11 @@ struct td_index {
 };
 
 struct dso {
+#if DL_FDPIC
+	struct fdpic_loadmap *loadmap;
+#else
 	unsigned char *base;
+#endif
 	char *name;
 	size_t *dynv;
 	struct dso *next, *prev;
@@ -75,6 +79,16 @@ struct dso {
 	struct td_index *td_index;
 	struct dso *fini_next;
 	char *shortname;
+#if DL_FDPIC
+	unsigned char *base;
+#else
+	struct fdpic_loadmap *loadmap;
+#endif
+	struct funcdesc {
+		void *addr;
+		size_t *got;
+	} *funcdescs;
+	size_t *got;
 	char buf[];
 };
 
@@ -112,6 +126,8 @@ static struct debug debug;
 static size_t tls_cnt, tls_offset, tls_align = MIN_TLS_ALIGN;
 static size_t static_tls_cnt;
 static pthread_mutex_t init_fini_lock = { ._m_type = PTHREAD_MUTEX_RECURSIVE };
+static struct fdpic_loadmap *app_loadmap;
+static struct fdpic_dummy_loadmap app_dummy_loadmap;
 
 struct debug *_dl_debug_addr = &debug;
 
@@ -123,7 +139,20 @@ static int dl_strcmp(const char *l, const char *r)
 #define strcmp(l,r) dl_strcmp(l,r)
 
 /* Compute load address for a virtual address in a given dso. */
+#ifdef DL_FDPIC
+static void *laddr(const struct dso *p, size_t v)
+{
+	size_t j=0;
+	if (!p->loadmap) return p->base + v;
+	for (j=0; v-p->loadmap->segs[j].p_vaddr >= p->loadmap->segs[j].p_memsz; j++);
+	return (void *)(v - p->loadmap->segs[j].p_vaddr + p->loadmap->segs[j].addr);
+}
+#define fpaddr(p, v) ((void (*)())&(struct funcdesc){ \
+	laddr(p, v), (p)->got })
+#else
 #define laddr(p, v) (void *)((p)->base + (v))
+#define fpaddr(p, v) ((void (*)())laddr(p, v))
+#endif
 
 static void decode_vec(size_t *v, size_t *a, size_t cnt)
 {
@@ -284,7 +313,7 @@ static void do_relocs(struct dso *dso, size_t *rel, size_t rel_size, size_t stri
 	}
 
 	for (; rel_size; rel+=stride, rel_size-=stride*sizeof(size_t)) {
-		if (skip_relative && IS_RELATIVE(rel[1])) continue;
+		if (skip_relative && IS_RELATIVE(rel[1], dso->syms)) continue;
 		type = R_TYPE(rel[1]);
 		if (type == REL_NONE) continue;
 		sym_index = R_SYM(rel[1]);
@@ -293,7 +322,9 @@ static void do_relocs(struct dso *dso, size_t *rel, size_t rel_size, size_t stri
 			sym = syms + sym_index;
 			name = strings + sym->st_name;
 			ctx = type==REL_COPY ? head->next : head;
-			def = find_sym(ctx, name, type==REL_PLT);
+			def = (sym->st_info&0xf) == STT_SECTION
+				? (struct symdef){ .dso = dso, .sym = sym }
+				: find_sym(ctx, name, type==REL_PLT);
 			if (!def.sym && (sym->st_shndx != SHN_UNDEF
 			    || sym->st_info>>4 != STB_WEAK)) {
 				error("Error relocating %s: %s: symbol not found",
@@ -349,6 +380,15 @@ static void do_relocs(struct dso *dso, size_t *rel, size_t rel_size, size_t stri
 			*(uint32_t *)reloc_addr = sym_val + addend
 				- (size_t)reloc_addr;
 			break;
+		case REL_FUNCDESC:
+			*reloc_addr = def.sym ? (size_t)(def.dso->funcdescs
+				+ (def.sym - def.dso->syms)) : 0;
+			break;
+		case REL_FUNCDESC_VAL:
+			if ((sym->st_info&0xf) == STT_SECTION) *reloc_addr += sym_val;
+			else *reloc_addr = sym_val;
+			reloc_addr[1] = def.sym ? (size_t)def.dso->got : 0;
+			break;
 		case REL_DTPMOD:
 			*reloc_addr = def.dso->tls_id;
 			break;
@@ -430,6 +470,7 @@ static void reclaim_gaps(struct dso *dso)
 	Phdr *ph = dso->phdr;
 	size_t phcnt = dso->phnum;
 
+	if (DL_FDPIC) return; // FIXME
 	for (; phcnt--; ph=(void *)((char *)ph+dso->phentsize)) {
 		if (ph->p_type!=PT_LOAD) continue;
 		if ((ph->p_flags&(PF_R|PF_W))!=(PF_R|PF_W)) continue;
@@ -698,6 +739,8 @@ static void decode_dyn(struct dso *p)
 		p->rpath_orig = p->strings + dyn[DT_RPATH];
 	if (dyn[0]&(1<<DT_RUNPATH))
 		p->rpath_orig = p->strings + dyn[DT_RUNPATH];
+	if (dyn[0]&(1<<DT_PLTGOT))
+		p->got = laddr(p, dyn[DT_PLTGOT]);
 	if (search_vec(p->dynv, dyn, DT_GNU_HASH))
 		p->ghashtab = laddr(p, *dyn);
 	if (search_vec(p->dynv, dyn, DT_VERSYM))
@@ -723,6 +766,46 @@ static size_t count_syms(struct dso *p)
 	return nsym;
 }
 
+static void *dl_mmap(size_t n)
+{
+	void *p;
+	int prot = PROT_READ|PROT_WRITE, flags = MAP_ANONYMOUS|MAP_PRIVATE;
+#ifdef SYS_mmap2
+	p = (void *)__syscall(SYS_mmap2, 0, n, prot, flags, -1, 0);
+#else
+	p = (void *)__syscall(SYS_mmap, 0, n, prot, flags, -1, 0);
+#endif
+	return p == MAP_FAILED ? 0 : p;
+}
+
+static void makefuncdescs(struct dso *p)
+{
+	static int self_done;
+	size_t nsym = count_syms(p);
+	size_t i, size = nsym * sizeof(*p->funcdescs);
+
+	if (!self_done) {
+		p->funcdescs = dl_mmap(size);
+		self_done = 1;
+	} else {
+		p->funcdescs = malloc(size);
+	}
+	if (!p->funcdescs) {
+		if (!runtime) a_crash();
+		error("Error allocating function descriptors for %s", p->name);
+		longjmp(*rtld_fail, 1);
+	}
+	for (i=0; i<nsym; i++) {
+		if ((p->syms[i].st_info&0xf)==STT_FUNC && p->syms[i].st_shndx) {
+			p->funcdescs[i].addr = laddr(p, p->syms[i].st_value);
+			p->funcdescs[i].got = p->got;
+		} else {
+			p->funcdescs[i].addr = 0;
+			p->funcdescs[i].got = 0;
+		}
+	}
+}
+
 static struct dso *load_library(const char *name, struct dso *needed_by)
 {
 	char buf[2*NAME_MAX+2];
@@ -902,6 +985,8 @@ static struct dso *load_library(const char *name, struct dso *needed_by)
 	p->prev = tail;
 	tail = p;
 
+	if (DL_FDPIC) makefuncdescs(p);
+
 	if (ldd_mode) dprintf(1, "\t%s => %s (%p)\n", name, pathname, p->base);
 
 	return p;
@@ -1034,7 +1119,7 @@ static void do_fini()
 		}
 #ifndef NO_LEGACY_INITFINI
 		if ((dyn[0] & (1<<DT_FINI)) && dyn[DT_FINI])
-			((void (*)(void))laddr(p, dyn[DT_FINI]))();
+			fpaddr(p, dyn[DT_FINI])();
 #endif
 	}
 }
@@ -1057,7 +1142,7 @@ static void do_init_fini(struct dso *p)
 		}
 #ifndef NO_LEGACY_INITFINI
 		if ((dyn[0] & (1<<DT_INIT)) && dyn[DT_INIT])
-			((void (*)(void))laddr(p, dyn[DT_INIT]))();
+			fpaddr(p, dyn[DT_INIT])();
 #endif
 		if (dyn[0] & (1<<DT_INIT_ARRAY)) {
 			size_t n = dyn[DT_INIT_ARRAYSZ]/sizeof(size_t);
@@ -1196,16 +1281,33 @@ static void update_tls_size()
 
 void __dls2(unsigned char *base, size_t *sp)
 {
-	Ehdr *ehdr = (void *)base;
-	ldso.base = base;
+	if (DL_FDPIC) {
+		void *p1 = (void *)sp[-2];
+		void *p2 = (void *)sp[-1];
+		if (!p1) {
+			size_t *auxv, aux[AUX_CNT];
+			for (auxv=sp+1+*sp+1; *auxv; auxv++); auxv++;
+			decode_vec(auxv, aux, AUX_CNT);
+			if (aux[AT_BASE]) ldso.base = (void *)aux[AT_BASE];
+			else ldso.base = (void *)(aux[AT_PHDR] & -4096);
+		}
+		app_loadmap = p2 ? p1 : 0;
+		ldso.loadmap = p2 ? p2 : p1;
+		ldso.base = laddr(&ldso, 0);
+	} else {
+		ldso.base = base;
+	}
+	Ehdr *ehdr = (void *)ldso.base;
 	ldso.name = ldso.shortname = "libc.so";
 	ldso.global = 1;
 	ldso.phnum = ehdr->e_phnum;
-	ldso.phdr = (void *)(base + ehdr->e_phoff);
+	ldso.phdr = laddr(&ldso, ehdr->e_phoff);
 	ldso.phentsize = ehdr->e_phentsize;
 	kernel_mapped_dso(&ldso);
 	decode_dyn(&ldso);
 
+	if (DL_FDPIC) makefuncdescs(&ldso);
+
 	/* Prepare storage for to save clobbered REL addends so they
 	 * can be reused in stage 3. There should be very few. If
 	 * something goes wrong and there are a huge number, abort
@@ -1217,7 +1319,7 @@ void __dls2(unsigned char *base, size_t *sp)
 	size_t symbolic_rel_cnt = 0;
 	apply_addends_to = rel;
 	for (; rel_size; rel+=2, rel_size-=2*sizeof(size_t))
-		if (!IS_RELATIVE(rel[1])) symbolic_rel_cnt++;
+		if (!IS_RELATIVE(rel[1], ldso.syms)) symbolic_rel_cnt++;
 	if (symbolic_rel_cnt >= ADDEND_LIMIT) a_crash();
 	size_t addends[symbolic_rel_cnt+1];
 	saved_addends = addends;
@@ -1231,7 +1333,8 @@ void __dls2(unsigned char *base, size_t *sp)
 	 * symbolically as a barrier against moving the address
 	 * load across the above relocation processing. */
 	struct symdef dls3_def = find_sym(&ldso, "__dls3", 0);
-	((stage3_func)laddr(&ldso, dls3_def.sym->st_value))(sp);
+	if (DL_FDPIC) ((stage3_func)&ldso.funcdescs[dls3_def.sym-ldso.syms])(sp);
+	else ((stage3_func)laddr(&ldso, dls3_def.sym->st_value))(sp);
 }
 
 /* Stage 3 of the dynamic linker is called with the dynamic linker/libc
@@ -1298,6 +1401,7 @@ _Noreturn void __dls3(size_t *sp)
 				app.tls_align = phdr->p_align;
 			}
 		}
+		if (DL_FDPIC) app.loadmap = app_loadmap;
 		if (app.tls_size) app.tls_image = laddr(&app, tls_image);
 		if (interp_off) ldso.name = laddr(&app, interp_off);
 		if ((aux[0] & (1UL<<AT_EXECFN))
@@ -1384,6 +1488,16 @@ _Noreturn void __dls3(size_t *sp)
 	}
 	app.global = 1;
 	decode_dyn(&app);
+	if (DL_FDPIC) {
+		makefuncdescs(&app);
+		if (!app.loadmap) {
+			app.loadmap = (void *)&app_dummy_loadmap;
+			app.loadmap->nsegs = 1;
+			app.loadmap->segs[0].addr = (size_t)app.base;
+			app.loadmap->segs[0].p_memsz = -1;
+		}
+		argv[-3] = (void *)app.loadmap;
+	}
 
 	/* Attach to vdso, if provided by the kernel */
 	if (search_vec(auxv, &vdso_base, AT_SYSINFO_EHDR)) {
@@ -1512,6 +1626,8 @@ void *dlopen(const char *file, int mode)
 				free(p->td_index);
 				p->td_index = tmp;
 			}
+			if (p->funcdescs)
+				free(p->funcdescs);
 			if (p->rpath != p->rpath_orig)
 				free(p->rpath);
 			free(p->deps);