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$prog.ape support (#977)

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* ape loader: $prog.ape + login shell support

If the ape loader is invoked with `$0 = $prog.ape`, then it searches for
a `$prog` in the same directory as it and loads that. In particular, the
loader searches the `PATH` for an executable named `$prog.ape`, then for
an executable named `$prog` in the same directory. If the former but not
the latter is found, the search terminates with an error.

It also handles the special case of getting started as `-$SHELL`, which
getty uses to indicate that the shell is a login shell. The path is not
searched in this case, and the program location is read straight out of
the `SHELL` variable.

It is now possible to have `/usr/local/bin/zsh.ape` act as a login shell
for a `/usr/local/bin/zsh` αpε, insofar as the program will get started
with the 'correct' args. Unfortunately, many things break if `$0` is not
the actual full path of the executable being run; for example, backspace
does not update the display properly.

To work around the brokenness introduced by not having `$0` be the full
path of the binary, we cut the leading `-` out of `argv[0]` if present.
This gets the loader's behavior with `$prog.ape` up to par, but doesn't
tell login shells that they are login shells.

So we introduce a hack to accomplish that: if ape is run as `-$prog.ape`
and the shell is `$prog`, the binary that is loaded has a `-l` flag put
into its first argument.

As of this commit, αpε binaries can be used as login shells on OSX.

* if islogin, execfn = shell

Prior to this, execfn was not being properly set for login shells that
did not receive `$_`, which was the case for iTerm2 on Mac. There were
no observable consequences of this, but fixing it seems good anyway.

* Fix auxv location calculation

In the non-login-shell case, it was leaving a word of uninitialized
memory at `envp[i] + 1`. This reuses the previous calculation based
on `envp`.
This commit is contained in:
Jōshin 2023-12-03 22:39:32 -05:00 committed by GitHub
parent 8dd348067b
commit 2a3813c6cf
No known key found for this signature in database
GPG key ID: 4AEE18F83AFDEB23
1 changed files with 71 additions and 19 deletions
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90
ape/ape-m1.c
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@ -194,6 +194,7 @@ union ElfPhdrBuf {
struct PathSearcher {
int literally;
int indirect;
unsigned long namelen;
const char *name;
const char *syspath;
@ -220,16 +221,8 @@ static int StrCmp(const char *l, const char *r) {
}
static const char *BaseName(const char *s) {
int c;
const char *b = "";
if (s) {
while ((c = *s++)) {
if (c == '/') {
b = s;
}
}
}
return b;
const char *b = strrchr(s, '/');
return b ? b + 1 : s;
}
static char *GetEnv(char **p, const char *s) {
@ -297,6 +290,14 @@ static long Print(int fd, const char *s, ...) {
return write(fd, b, n);
}
static int GetIndirectOffset(const char *arg0) {
char *tail = strrchr(arg0, '.');
if (tail && !StrCmp(tail + 1, "ape")) {
return tail - arg0;
}
return 0;
}
static void Perror(const char *thing, long rc, const char *reason) {
char ibuf[21];
ibuf[0] = 0;
@ -316,7 +317,17 @@ static char AccessCommand(struct PathSearcher *ps, unsigned long pathlen) {
if (pathlen && ps->path[pathlen - 1] != '/') ps->path[pathlen++] = '/';
memmove(ps->path + pathlen, ps->name, ps->namelen);
ps->path[pathlen + ps->namelen] = 0;
return !access(ps->path, X_OK);
if (!access(ps->path, X_OK)) {
if (ps->indirect) {
ps->namelen -= 4;
ps->path[pathlen + ps->namelen] = 0;
if (access(ps->path, X_OK) < 0) {
Pexit(ps->path, -errno, "access(X_OK)");
}
}
return 1;
}
return 0;
}
static char SearchPath(struct PathSearcher *ps) {
@ -870,11 +881,11 @@ static const char *TryElf(struct ApeLoader *M, union ElfEhdrBuf *ebuf,
int main(int argc, char **argv, char **envp) {
unsigned i;
int c, n, fd, rc;
struct ApeLoader *M;
long *sp, *sp2, *auxv;
union ElfEhdrBuf *ebuf;
char *p, *pe, *exe, *prog, *execfn;
int c, islogin, n, fd, rc;
char *p, *pe, *dash_l, *exe, *prog, *shell, *execfn;
/* allocate loader memory in program's arg block */
n = sizeof(struct ApeLoader);
@ -936,8 +947,21 @@ int main(int argc, char **argv, char **envp) {
M->lib.dlclose = dlclose;
M->lib.dlerror = dlerror;
/* there is a common convention of shells being told that they
are login shells via the OS prepending a - to their argv[0].
the APE system doesn't like it when argv[0] is not the full
path of the binary. to rectify this, the loader puts a "-l"
flag in argv[1] and ignores the dash. */
if ((islogin = argc > 0 && *argv[0] == '-' && (shell = GetEnv(envp, "SHELL"))
&& !StrCmp(argv[0] + 1, BaseName(shell)))) {
execfn = shell;
dash_l = __builtin_alloca(3);
memmove(dash_l, "-l", 3);
} else {
execfn = argc > 0 ? argv[0] : 0;
}
/* getenv("_") is close enough to at_execfn */
execfn = argc > 0 ? argv[0] : 0;
for (i = 0; envp[i]; ++i) {
if (envp[i][0] == '_' && envp[i][1] == '=') {
execfn = envp[i] + 2;
@ -951,20 +975,47 @@ int main(int argc, char **argv, char **envp) {
/* create new bottom of stack for spawned program
system v abi aligns this on a 16-byte boundary
grows down the alloc by poking the guard pages */
n = (auxv - sp + AUXV_WORDS + 1) * sizeof(long);
n = (auxv - sp + islogin + AUXV_WORDS + 1) * sizeof(long);
sp2 = (long *)__builtin_alloca(n);
if ((long)sp2 & 15) ++sp2;
for (; n > 0; n -= pagesz) {
((char *)sp2)[n - 1] = 0;
}
memmove(sp2, sp, (auxv - sp) * sizeof(long));
if (islogin) {
memmove(sp2, sp, 2 * sizeof(long));
*((char **)sp2 + 2) = dash_l;
memmove(sp2 + 3, sp + 2, (auxv - sp - 2) * sizeof(long));
++argc;
sp2[0] = argc;
} else {
memmove(sp2, sp, (auxv - sp) * sizeof(long));
}
argv = (char **)(sp2 + 1);
envp = (char **)(sp2 + 1 + argc + 1);
auxv = sp2 + (auxv - sp);
auxv = (long *)(envp + i + 1);
sp = sp2;
/* interpret command line arguments */
if ((M->ps.literally = argc >= 3 && !StrCmp(argv[1], "-"))) {
if ((M->ps.indirect = argc > 0 ? GetIndirectOffset(argv[0]) : 0)) {
M->ps.literally = 0;
/* if argv[0] is $prog.ape, then we strip off the .ape and run
$prog. This allows you to use symlinks to trick the OS when
a native executable is required. For example, let's say you
want to use the APE binary /opt/cosmos/bin/bash as a system
shell in /etc/shells, or perhaps in shebang lines like e.g.
`#!/opt/cosmos/bin/bash`. That won't work with APE normally,
but it will if you say:
ln -sf /usr/local/bin/ape /opt/cosmos/bin/bash.ape
and then use #!/opt/cosmos/bin/bash.ape instead. */
prog = (char *)sp[1];
argc = sp[0];
argv = (char **)(sp + 1);
if (islogin) {
++argv[0];
prog = shell;
}
} else if ((M->ps.literally = argc >= 3 && !StrCmp(argv[1], "-"))) {
/* if the first argument is a hyphen then we give the user the
power to change argv[0] or omit it entirely. most operating
systems don't permit the omission of argv[0] but we do, b/c
@ -975,6 +1026,7 @@ int main(int argc, char **argv, char **envp) {
} else if (argc < 2) {
Emit("usage: ape PROG [ARGV1,ARGV2,...]\n"
" ape - PROG [ARGV0,ARGV1,...]\n"
" ($0 = PROG.ape) [ARGV1,ARGV2,...]\n"
"actually portable executable loader silicon 1.9\n"
"copyright 2023 justine alexandra roberts tunney\n"
"https://justine.lol/ape.html\n");
@ -1006,7 +1058,7 @@ int main(int argc, char **argv, char **envp) {
/* resolve argv[0] to reflect path search */
if (argc > 0 && ((*prog != '/' && *exe == '/' && !StrCmp(prog, argv[0])) ||
!StrCmp(BaseName(prog), argv[0]))) {
M->ps.indirect || !StrCmp(BaseName(prog), argv[0]))) {
argv[0] = exe;
}