Support baseline POSIX standard

Many more configuration checks have been added in order to in theory
support baseline POSIX systems, without XSI extensions. Bugs are now
fixed in interfaces like SIOCGIFCONF, getrandom(), getresuid(), etc.
Executable loading is greatly improved. Blink will now handle script
shebang lines. Detection of non-Linux binaries has improved too.

.gitignore

@@ -11,6 +11,7 @@ blink.log
 /TAGS
 /HTAGS
 /config.h
+/config.mk
 /config.log
 /*.dump
 /gmon.out

Makefile

@@ -3,7 +3,7 @@
 
 SHELL = /bin/sh
 MAKEFLAGS += --no-builtin-rules
-ARCHITECTURES = x86_64 x86_64-gcc49 i486 aarch64 riscv64 arm mips s390x mipsel mips64 mips64el powerpc powerpc64le
+ARCHITECTURES = x86_64 x86_64-gcc49 i486 aarch64 arm mips s390x mipsel mips64 mips64el powerpc powerpc64le
 
 .SUFFIXES:
 .DELETE_ON_ERROR:
@@ -20,10 +20,7 @@ MODE := $(m)
 endif
 endif
 
-HOST_SYSTEM := $(shell uname -s)
-HOST_ARCH := $(shell uname -m)
-HOST_OS := $(shell uname -o 2>/dev/null)
-TMPDIR := $(shell mkdir -p o/tmp; echo $(shell pwd)/o/tmp)
+include config.mk
 
 ifneq ($(HOST_SYSTEM), Linux)
 VM = o/$(MODE)/blink/blink
@@ -167,7 +164,7 @@ HTAGS:	o/$(MODE)/hdrs.txt $(HDRS)
 	build/htags -L $< -o $@
 
 clean:
-	rm -f $(OBJS) o/$(MODE)/blink/blink o/$(MODE)/blink/blinkenlights o/$(MODE)/blink/blink.a
+	rm -f $(OBJS) o/$(MODE)/blink/blink o/$(MODE)/blink/blinkenlights o/$(MODE)/blink/blink.a o/$(MODE)/third_party/zlib/zlib.a
 
 distclean:
 	rm -rf o

README.md

@@ -14,7 +14,7 @@ do the same thing as the `qemu-x86_64` command, except that
 1. Blink is 196kb in size (or 126kb if optional features are disabled),
    whereas the qemu-x86_64 executable is 4mb in size.
 
-2. Blink will run your Linux binaries on any POSIX platform, whereas
+2. Blink will run your Linux binaries on any POSIX system, whereas
    qemu-x86_64 only supports Linux.
 
 3. Blink goes 2x faster than qemu-x86_64 on some benchmarks, such as SSE
@@ -44,11 +44,11 @@ following platforms:
 
 Blink depends on the following libraries:
 
-- libc (POSIX.1-2017)
+- libc (POSIX.1-2017 baseline, XSI not required)
 
 Blink can be compiled on UNIX systems that have:
 
-- A C11 compiler (e.g. GCC 4.9.4+)
+- A C11 compiler with atomics (e.g. GCC 4.9.4+)
 - Modern GNU Make (i.e. not the one that comes with XCode)
 
 The instructions for compiling Blink are as follows:
@@ -129,6 +129,14 @@ You can hunt down bugs in Blink using the following build modes:
 - `MODE=ubsan` to find violations of the C standard
 - `MODE=msan` helps find uninitialized memory errors
 
+You can check Blink's compliance with the POSIX standard using the
+following configuration flags:
+
+```sh
+./configure --posix  # only use c11 with baseline posix standard
+./configure --xopen  # same but also allow use of xsi extensions
+```
+
 ### Testing
 
 Blink is tested primarily using precompiled binaries downloaded

blink/ancillary.c

@@ -63,7 +63,7 @@ static int AppendCmsg(struct Machine *m, struct msghdr *msg, int level,
   return 0;
 }
 
-#ifdef SCM_CREDENTIALS
+#ifdef HAVE_SCM_CREDENTIALS
 static int SendScmCredentials(struct Machine *m, struct msghdr *msg,
                               const struct ucred_linux *payload,
                               size_t elements) {
@@ -103,7 +103,7 @@ static ssize_t GetAncillaryElementLength(const struct cmsghdr_linux *gcmsg) {
         case SCM_RIGHTS_LINUX:
           return 4;
 #endif
-#ifdef SCM_CREDENTIALS
+#ifdef HAVE_SCM_CREDENTIALS
         case SCM_CREDENTIALS_LINUX:
           return sizeof(struct ucred_linux);
 #endif
@@ -179,7 +179,7 @@ int SendAncillary(struct Machine *m, struct msghdr *msg,
               return -1;
             break;
 #endif
-#ifdef SCM_CREDENTIALS
+#ifdef HAVE_SCM_CREDENTIALS
           case SCM_CREDENTIALS_LINUX:
             if (SendScmCredentials(m, msg, (const struct ucred_linux *)payload,
                                    elements) == -1)
@@ -271,7 +271,7 @@ static i64 ReceiveScmRights(struct Machine *m, struct msghdr_linux *gm,
 }
 #endif
 
-#ifdef SCM_CREDENTIALS
+#ifdef HAVE_SCM_CREDENTIALS
 static i64 ReceiveScmCredentials(struct Machine *m, struct msghdr_linux *gm,
                                  struct cmsghdr *cmsg, u64 offset) {
   struct ucred_linux gucred;
@@ -301,7 +301,7 @@ static i64 ReceiveControlMessage(struct Machine *m, struct msghdr_linux *gm,
       return ReceiveScmRights(m, gm, cmsg, offset, flags);
     }
 #endif
-#ifdef SCM_CREDENTIALS
+#ifdef HAVE_SCM_CREDENTIALS
     if (cmsg->cmsg_type == SCM_CREDENTIALS) {
       return ReceiveScmCredentials(m, gm, cmsg, offset);
     }

blink/argv.c

@@ -66,13 +66,14 @@ static long GetGuestPageSize(struct Machine *m) {
   }
 }
 
-void LoadArgv(struct Machine *m, char *prog, char **args, char **vars) {
+void LoadArgv(struct Machine *m, char *execfn, char *prog, char **args,
+              char **vars) {
   u8 *bytes;
   char rng[16];
   struct Elf *elf;
   i64 sp, *p, *bloc;
   size_t i, narg, nenv, naux, nall;
-  GetRandom(rng, 16);
+  unassert(GetRandom(rng, 16, 0) == 16);
   elf = &m->system->elf;
   naux = 10;
   if (elf->at_entry) {
@@ -95,7 +96,7 @@ void LoadArgv(struct Machine *m, char *prog, char **args, char **vars) {
   PUSH_AUXV(AT_PAGESZ_LINUX, GetGuestPageSize(m));
   PUSH_AUXV(AT_CLKTCK_LINUX, sysconf(_SC_CLK_TCK));
   PUSH_AUXV(AT_RANDOM_LINUX, PushBuffer(m, rng, 16));
-  PUSH_AUXV(AT_EXECFN_LINUX, PushString(m, g_blink_path));
+  PUSH_AUXV(AT_EXECFN_LINUX, PushString(m, execfn));
   if (elf->at_entry) {
     PUSH_AUXV(AT_PHDR_LINUX, elf->at_phdr);
     PUSH_AUXV(AT_PHENT_LINUX, elf->at_phent);

blink/blink.c

@@ -111,7 +111,7 @@ static void OnSigSegv(int sig, siginfo_t *si, void *ptr) {
   siglongjmp(g_machine->onhalt, kMachineSegmentationFault);
 }
 
-static int Exec(char *prog, char **argv, char **envp) {
+static int Exec(char *execfn, char *prog, char **argv, char **envp) {
   int i;
   sigset_t oldmask;
   struct Machine *old;
@@ -123,7 +123,7 @@ static int Exec(char *prog, char **argv, char **envp) {
   g_machine->system->exec = Exec;
   if (!old) {
     // this is the first time a program is being loaded
-    LoadProgram(g_machine, prog, argv, envp);
+    LoadProgram(g_machine, execfn, prog, argv, envp);
     SetupCod(g_machine);
     for (i = 0; i < 10; ++i) {
       AddStdFd(&g_machine->system->fds, i);
@@ -137,7 +137,7 @@ static int Exec(char *prog, char **argv, char **envp) {
     }
     memcpy(g_machine->system->rlim, old->system->rlim,
            sizeof(old->system->rlim));
-    LoadProgram(g_machine, prog, argv, envp);
+    LoadProgram(g_machine, execfn, prog, argv, envp);
     g_machine->system->fds.list = old->system->fds.list;
     old->system->fds.list = 0;
     // releasing the execve() lock must come after unlocking fds
@@ -286,5 +286,6 @@ int main(int argc, char *argv[]) {
     WriteErrorString("\n");
     exit(127);
   }
-  return Exec(g_pathbuf, argv + optind_ + FLAG_zero, environ);
+  argv[optind_] = g_pathbuf;
+  return Exec(g_pathbuf, g_pathbuf, argv + optind_ + FLAG_zero, environ);
 }