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Loaders rewrite argv[0] for old binaries (#1170)

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For this to work, a loader has to be able to tell the difference between
an ‘old’ and a ‘new’ binary. This is achieved via a repurposing of ELF’s
e_flags field. We previously tried to use the padding in e_ident for it,
but binutils was resetting it to zero in e.g. strip.

This introduces one new ELF flag for cosmopolitan binaries. It is called
`EF_APE_MODERN`. We choose 0x101ca75, "lol cat 5".

It should now be safe to install the ape loader binfmt registration with
the `P` flag.
This commit is contained in:
Jōshin 2024-05-07 17:42:18 -07:00 • committed by GitHub
parent 57c0b065c8
commit 7d31fc311a
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5 changed files with 27 additions and 3 deletions
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9
ape/ape-m1.c
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@ -146,6 +146,9 @@ struct Syslib {
#define AT_RANDOM 25
#define AT_EXECFN 31
#define EF_APE_MODERN 0x101ca75
#define EF_APE_MODERN_MASK 0x1ffffff
#define AUXV_WORDS 31
/* from the xnu codebase */
@ -799,7 +802,7 @@ __attribute__((__noreturn__)) static void Spawn(const char *exe, int fd,
}
static const char *TryElf(struct ApeLoader *M, union ElfEhdrBuf *ebuf,
const char *exe, int fd, long *sp, long *auxv,
char *exe, int fd, long *sp, long *auxv,
char *execfn) {
long i, rc;
unsigned size;
@ -820,6 +823,10 @@ static const char *TryElf(struct ApeLoader *M, union ElfEhdrBuf *ebuf,
if (e->e_machine != EM_AARCH64) {
return "couldn't find ELF header with ARM64 machine type";
}
if ((e->e_flags & EF_APE_MODERN_MASK) != EF_APE_MODERN && sp[0] > 0) {
/* change argv[0] to resolved path for older binaries */
((char **)(sp + 1))[0] = exe;
}
if (e->e_phentsize != sizeof(struct ElfPhdr)) {
Pexit(exe, 0, "e_phentsize is wrong");
}