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Work around Rosetta clobbering startup registers on M1 Macs (issue #429)

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Rosetta doesn't correctly respect the startup registers as defined in LC_UNIXTHREAD
which makes platform detection go awry. But at least Rosetta appears to consistently
set rbx to 0x00000000ffffffff and rdx to 0x0000000000000001 at startup for every
x64 executable I could get my hands on. So we use that to detect Rosetta's presence
and set up the correct registers for XNU.

Thanks to @pkulchenko and @jart for pointers on getting this done :)
This commit is contained in:
Daniil Kulchenko 2022-06-26 23:11:50 -07:00
parent a6f65eea7c
commit a7bab48b78
4 changed files with 38 additions and 4 deletions
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13
ape/loader-elf.S
View file

@ -213,7 +213,18 @@ macho: .long 0xFEEDFACE+1
// //
// @see APE_LOADER_ENTRY // @see APE_LOADER_ENTRY
// @see ape/loader.h // @see ape/loader.h
_start: mov %rsp,%rsi _start:
// Hack for detecting M1 Rosetta environment.
// https://github.com/jart/cosmopolitan/issues/429#issuecomment-1166704377
cmp $-1,%ebx
jne 0f
cmp $+1,%edx
jne 0f
mov $XNU,%dl
mov $0,%rcx
0: mov %rsp,%rsi
jmp ApeLoader jmp ApeLoader
.endfn _start,globl .endfn _start,globl

13
ape/loader-macho.S
View file

@ -113,7 +113,18 @@ macho: .long 0xFEEDFACE+1
.endobj macho,globl .endobj macho,globl
.align 64 .align 64
_start: mov %rsp,%rsi _start:
// Hack for detecting M1 Rosetta environment.
// https://github.com/jart/cosmopolitan/issues/429#issuecomment-1166704377
cmp $-1,%ebx
jne 0f
cmp $+1,%edx
jne 0f
mov $XNU,%dl
mov $0,%rcx
0: mov %rsp,%rsi
jmp ApeLoader jmp ApeLoader
.endfn _start,globl .endfn _start,globl

4
ape/loader.c
View file

@ -595,11 +595,11 @@ __attribute__((__noreturn__)) void ApeLoader(long di, long *sp, char dl,
// detect freebsd // detect freebsd
if (handoff) { if (handoff) {
os = handoff->os; os = handoff->os;
} else if (SupportsXnu() && dl == XNU) {
os = XNU;
} else if (SupportsFreebsd() && di) { } else if (SupportsFreebsd() && di) {
os = FREEBSD; os = FREEBSD;
sp = (long *)di; sp = (long *)di;
} else if (SupportsXnu() && dl == XNU) {
os = XNU;
} else { } else {
os = 0; os = 0;
} }

12
libc/crt/crt.S
View file

@ -31,6 +31,18 @@
// @noreturn // @noreturn
_start: _start:
#if SupportsXnu()
// Hack for detecting M1 Rosetta environment.
// https://github.com/jart/cosmopolitan/issues/429#issuecomment-1166704377
cmp $-1,%ebx
jne 0f
cmp $+1,%edx
jne 0f
mov $XNU,%cl
mov $0,%rdi
0:
#endif
#if SupportsFreebsd() #if SupportsFreebsd()
// detect free besiyata dishmaya // detect free besiyata dishmaya
test %rdi,%rdi test %rdi,%rdi