Add a "fork" of musl as //fusl.

fusl/src/ldso/dlstart.c

+#include <stddef.h>
+#include "dynlink.h"
+
+#ifdef SHARED
+
+#ifndef START
+#define START "_dlstart"
+#endif
+
+#include "crt_arch.h"
+
+#ifndef GETFUNCSYM
+#define GETFUNCSYM(fp, sym, got) do { \
+        __attribute__((__visibility__("hidden"))) void sym(); \
+        static void (*static_func_ptr)() = sym; \
+        __asm__ __volatile__ ( "" : "+m"(static_func_ptr) : : "memory"); \
+        *(fp) = static_func_ptr; } while(0)
+#endif
+
+__attribute__((__visibility__("hidden")))
+void _dlstart_c(size_t *sp, size_t *dynv)
+{
+        size_t i, aux[AUX_CNT], dyn[DYN_CNT];
+        size_t *rel, rel_size, base;
+
+        int argc = *sp;
+        char **argv = (void *)(sp+1);
+
+        for (i=argc+1; argv[i]; i++);
+        size_t *auxv = (void *)(argv+i+1);
+
+        for (i=0; i<AUX_CNT; i++) aux[i] = 0;
+        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
+         * virtual address in the PT_DYNAMIC program header. */
+        base = aux[AT_BASE];
+        if (!base) {
+                size_t phnum = aux[AT_PHNUM];
+                size_t phentsize = aux[AT_PHENT];
+                Phdr *ph = (void *)aux[AT_PHDR];
+                for (i=phnum; i--; ph = (void *)((char *)ph + phentsize)) {
+                        if (ph->p_type == PT_DYNAMIC) {
+                                base = (size_t)dynv - ph->p_vaddr;
+                                break;
+                        }
+                }
+        }
+
+        /* MIPS uses an ugly packed form for GOT relocations. Since we
+         * can't make function calls yet and the code is tiny anyway,
+         * it's simply inlined here. */
+        if (NEED_MIPS_GOT_RELOCS) {
+                size_t local_cnt = 0;
+                size_t *got = (void *)(base + dyn[DT_PLTGOT]);
+                for (i=0; dynv[i]; i+=2) if (dynv[i]==DT_MIPS_LOCAL_GOTNO)
+                        local_cnt = dynv[i+1];
+                for (i=0; i<local_cnt; i++) got[i] += base;
+        }
+
+        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], 0)) continue;
+                size_t *rel_addr = (void *)(base + rel[0]);
+                *rel_addr += base;
+        }
+
+        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], 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]);
+        dls2((void *)base, sp);
+}
+
+#endif