Add x86_64-linux-gnu emulator

I wanted a tiny scriptable meltdown proof way to run userspace programs
and visualize how program execution impacts memory. It helps to explain
how things like Actually Portable Executable works. It can show you how
the GCC generated code is going about manipulating matrices and more. I
didn't feel fully comfortable with Qemu and Bochs because I'm not smart
enough to understand them. I wanted something like gVisor but with much
stronger levels of assurances. I wanted a single binary that'll run, on
all major operating systems with an embedded GPL barrier ZIP filesystem
that is tiny enough to transpile to JavaScript and run in browsers too.

https://justine.storage.googleapis.com/emulator625.mp4

libc/calls/struct/metastat.h

@@ -1,5 +1,6 @@
 #ifndef COSMOPOLITAN_LIBC_CALLS_STRUCT_METASTAT_H_
 #define COSMOPOLITAN_LIBC_CALLS_STRUCT_METASTAT_H_
+#ifndef __STRICT_ANSI__
 #include "libc/calls/struct/stat.h"
 #if !(__ASSEMBLER__ + __LINKER__ + 0)
 COSMOPOLITAN_C_START_
@@ -52,4 +53,5 @@ union metastat {
 
 COSMOPOLITAN_C_END_
 #endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* !ANSI */
 #endif /* COSMOPOLITAN_LIBC_CALLS_STRUCT_METASTAT_H_ */

libc/calls/struct/metatermios.h

@@ -1,5 +1,6 @@
 #ifndef COSMOPOLITAN_LIBC_CALLS_STRUCT_METATERMIOS_H_
 #define COSMOPOLITAN_LIBC_CALLS_STRUCT_METATERMIOS_H_
+#ifndef __STRICT_ANSI__
 #include "libc/calls/struct/termios.h"
 #if !(__ASSEMBLER__ + __LINKER__ + 0)
 COSMOPOLITAN_C_START_
@@ -32,4 +33,5 @@ union metatermios {
 
 COSMOPOLITAN_C_END_
 #endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* !ANSI */
 #endif /* COSMOPOLITAN_LIBC_CALLS_STRUCT_METATERMIOS_H_ */

libc/calls/struct/sigaction-freebsd.h

@@ -0,0 +1,14 @@
+#ifndef COSMOPOLITAN_LIBC_CALLS_STRUCT_SIGACTION_FREEBSD_H_
+#define COSMOPOLITAN_LIBC_CALLS_STRUCT_SIGACTION_FREEBSD_H_
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+
+struct sigaction$freebsd {
+  intptr_t sa_handler;
+  uint32_t sa_flags;
+  struct sigset$freebsd {
+    uint32_t sig[4];
+  } sa_mask;
+};
+
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_LIBC_CALLS_STRUCT_SIGACTION_FREEBSD_H_ */

libc/calls/struct/sigaction-linux.h

@@ -0,0 +1,15 @@
+#ifndef COSMOPOLITAN_LIBC_CALLS_STRUCT_SIGACTION_LINUX_H_
+#define COSMOPOLITAN_LIBC_CALLS_STRUCT_SIGACTION_LINUX_H_
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+
+struct sigaction$linux {
+  intptr_t sa_handler;
+  uint64_t sa_flags;
+  void (*sa_restorer)(void);
+  struct sigset$linux {
+    uint32_t sig[2];
+  } sa_mask;
+};
+
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_LIBC_CALLS_STRUCT_SIGACTION_LINUX_H_ */

libc/calls/struct/sigaction-openbsd.h

@@ -0,0 +1,14 @@
+#ifndef COSMOPOLITAN_LIBC_CALLS_STRUCT_SIGACTION_OPENBSD_H_
+#define COSMOPOLITAN_LIBC_CALLS_STRUCT_SIGACTION_OPENBSD_H_
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+
+struct sigaction$openbsd {
+  intptr_t sa_handler;
+  struct sigset$openbsd {
+    uint32_t sig[1];
+  } sa_mask;
+  int32_t sa_flags;
+};
+
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_LIBC_CALLS_STRUCT_SIGACTION_OPENBSD_H_ */

libc/calls/struct/sigaction-xnu.h

@@ -0,0 +1,28 @@
+#ifndef COSMOPOLITAN_LIBC_CALLS_STRUCT_SIGACTION_XNU_H_
+#define COSMOPOLITAN_LIBC_CALLS_STRUCT_SIGACTION_XNU_H_
+#include "libc/calls/internal.h"
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+
+struct __darwin_ucontext;
+struct __darwin_siginfo;
+
+struct sigset$xnu {
+  uint32_t sig[1];
+};
+
+struct sigaction$xnu_in {
+  intptr_t sa_handler;
+  void (*sa_restorer)(void *, int, int, const struct __darwin_siginfo *,
+                      const struct __darwin_ucontext *);
+  struct sigset$xnu sa_mask;
+  int32_t sa_flags;
+};
+
+struct sigaction$xnu_out {
+  intptr_t sa_handler;
+  struct sigset$xnu sa_mask;
+  int32_t sa_flags;
+};
+
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_LIBC_CALLS_STRUCT_SIGACTION_XNU_H_ */

libc/calls/struct/sigaltstack.h

@@ -10,7 +10,5 @@ struct sigaltstack {
 
 typedef struct sigaltstack stack_t;
 
-static_assert(sizeof(stack_t) == 24);
-
 #endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
 #endif /* COSMOPOLITAN_LIBC_CALLS_STRUCT_SIGALTSTACK_H_ */

libc/calls/struct/sigset.h

@@ -2,7 +2,7 @@
 #define COSMOPOLITAN_LIBC_CALLS_STRUCT_SIGSET_H_
 #if !(__ASSEMBLER__ + __LINKER__ + 0)
 
-struct sigset {
+struct sigset {    /* cosmo abi (linux is uint64_t) */
   uint32_t sig[4]; /* ignore sig[2] and sig[3] (for freebsd) */
 } aligned(8);