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loader.c uses AT_FLAGS to communicate literally #1168

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loader.c uses AT_FLAGS to communicate literally #1168

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b77a3d5
loader.c uses AT_FLAGS to communicate literally
mrdomino May 6, 2024
f6cc903
Add TODO in test
mrdomino May 6, 2024
d259b4a
Zero out end-of-auxv
mrdomino May 6, 2024
7aef5c7
Set flags correctly
mrdomino May 6, 2024
e788df7
Only take the first flags
mrdomino May 6, 2024
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22 changes: 17 additions & 5 deletions ape/loader.c
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Original file line number Diff line number Diff line change
Expand Up @@ -949,7 +949,7 @@ EXTERN_C __attribute__((__noreturn__)) void ApeLoader(long di, long *sp,
char arg0, literally;
unsigned long pagesz;
union ElfEhdrBuf *ebuf;
long *auxv, *ap, *endp, *sp2;
long *auxv, *flags, *ap, *endp, *sp2;
char *p, *pe, *exe, *prog, **argv, **envp;

(void)Printf;
Expand Down Expand Up @@ -993,13 +993,15 @@ EXTERN_C __attribute__((__noreturn__)) void ApeLoader(long di, long *sp,
/* detect netbsd and find end of words */
pagesz = 0;
arg0 = 0;
flags = 0;
for (ap = auxv; ap[0]; ap += 2) {
if (ap[0] == AT_PAGESZ) {
pagesz = ap[1];
} else if (SupportsNetbsd() && !os && ap[0] == AT_EXECFN_NETBSD) {
os = NETBSD;
} else if (SupportsLinux() && ap[0] == AT_FLAGS) {
// TODO(mrdomino): maybe set/insert this when we are called as "ape -".
} else if (!flags && ap[0] == AT_FLAGS) {
// TODO(mrdomino): does anyone use auxv 8 for anything else?
flags = ap;
arg0 = !!(ap[1] & AT_FLAGS_PRESERVE_ARGV0);
}
}
Expand Down Expand Up @@ -1047,8 +1049,9 @@ EXTERN_C __attribute__((__noreturn__)) void ApeLoader(long di, long *sp,

/* 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 = (endp - sp + 1) * sizeof(long);
grows down the alloc by poking the guard pages
uses AT_FLAGS to say that argv[0] is preserved */
n = (endp - sp + 2 * !flags + 1) * sizeof(long);
sp2 = (long *)__builtin_alloca(n);
if ((long)sp2 & 15)
++sp2;
Expand All @@ -1059,6 +1062,15 @@ EXTERN_C __attribute__((__noreturn__)) void ApeLoader(long di, long *sp,
argv = (char **)(sp2 + 1);
envp = (char **)(sp2 + 1 + argc + 1);
auxv = sp2 + (auxv - sp);
if (flags) {
flags = flags - sp + sp2;
flags[1] |= literally * AT_FLAGS_PRESERVE_ARGV0;
} else {
flags = (endp - 1) - sp + sp2;
flags[0] = AT_FLAGS;
flags[1] = literally * AT_FLAGS_PRESERVE_ARGV0;
flags[2] = 0; /* end-of-auxv sentinel */
}
sp = sp2;

/* allocate ephemeral memory for reading file */
Expand Down
1 change: 1 addition & 0 deletions test/libc/calls/getprogramexecutablename_test.c
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Expand Up @@ -58,6 +58,7 @@ void SetUpOnce(void) {
skiptests = IsOpenbsd() || (IsXnu() && !IsXnuSilicon());
}
} else {
// TODO(mrdomino): test skiparg0 in child
skiparg0 = !(getauxval(AT_FLAGS) & AT_FLAGS_PRESERVE_ARGV0);
}
fprintf(stderr, loaded ? "loaded\n" : "not loaded\n");
Expand Down