From 76e92d1c9e2943de7093af14d58663fa2993e608 Mon Sep 17 00:00:00 2001 From: Keith Randall Date: Mon, 9 Apr 2018 16:00:54 -0700 Subject: [PATCH] runtime: use fixed TLS offsets on darwin/amd64 and darwin/386 Fixes #23617 Note that this CL does not affect darwin/arm and darwin/arm64, still TBD what, if anything, needs to be done for those. Change-Id: Ie1ee02a9f4d4d1fb9cd5dc432d900f926cc157db Reviewed-on: https://go-review.googlesource.com/105975 Reviewed-by: Ian Lance Taylor --- src/cmd/link/internal/ld/sym.go | 20 ++++--- src/runtime/cgo/gcc_darwin_386.c | 92 +----------------------------- src/runtime/cgo/gcc_darwin_amd64.c | 63 +------------------- src/runtime/sys_darwin_386.s | 11 ++-- src/runtime/sys_darwin_amd64.s | 9 ++- 5 files changed, 28 insertions(+), 167 deletions(-) diff --git a/src/cmd/link/internal/ld/sym.go b/src/cmd/link/internal/ld/sym.go index 6f019de8cc..7bc57eff8d 100644 --- a/src/cmd/link/internal/ld/sym.go +++ b/src/cmd/link/internal/ld/sym.go @@ -113,24 +113,30 @@ func (ctxt *Link) computeTLSOffset() { /* * OS X system constants - offset from 0(GS) to our TLS. - * Explained in src/runtime/cgo/gcc_darwin_*.c. */ case objabi.Hdarwin: switch ctxt.Arch.Family { default: log.Fatalf("unknown thread-local storage offset for darwin/%s", ctxt.Arch.Name) + /* + * For x86, Apple has reserved a slot in the TLS for Go. See issue 23617. + * That slot is at offset 0x30 on amd64, and 0x18 on 386. + * The slot will hold the G pointer. + * These constants should match those in runtime/sys_darwin_{386,amd64}.s + * and runtime/cgo/gcc_darwin_{386,amd64}.c. + */ + case sys.I386: + ctxt.Tlsoffset = 0x18 + + case sys.AMD64: + ctxt.Tlsoffset = 0x30 + case sys.ARM: ctxt.Tlsoffset = 0 // dummy value, not needed - case sys.AMD64: - ctxt.Tlsoffset = 0x8a0 - case sys.ARM64: ctxt.Tlsoffset = 0 // dummy value, not needed - - case sys.I386: - ctxt.Tlsoffset = 0x468 } } diff --git a/src/runtime/cgo/gcc_darwin_386.c b/src/runtime/cgo/gcc_darwin_386.c index 7d3c55cd56..c947f23073 100644 --- a/src/runtime/cgo/gcc_darwin_386.c +++ b/src/runtime/cgo/gcc_darwin_386.c @@ -9,89 +9,6 @@ #include "libcgo_unix.h" static void* threadentry(void*); -static pthread_key_t k1; - -#define magic1 (0x23581321U) - -static void -inittls(void) -{ - uint32 x; - pthread_key_t tofree[128], k; - int i, ntofree; - - /* - * Allocate thread-local storage slot for g. - * The key numbers start at 0x100, and we expect to be - * one of the early calls to pthread_key_create, so we - * should be able to get a pretty low number. - * - * In Darwin/386 pthreads, %gs points at the thread - * structure, and each key is an index into the thread-local - * storage array that begins at offset 0x48 within in that structure. - * It may happen that we are not quite the first function to try - * to allocate thread-local storage keys, so instead of depending - * on getting 0x100, we try for 0x108, allocating keys until - * we get the one we want and then freeing the ones we didn't want. - * - * Thus the final offset to use in %gs references is - * 0x48+4*0x108 = 0x468. - * - * The linker and runtime hard-code this constant offset - * from %gs where we expect to find g. - * Known to src/cmd/link/internal/ld/sym.go:/0x468 - * and to src/runtime/sys_darwin_386.s:/0x468 - * - * This is truly disgusting and a bit fragile, but taking care - * of it here protects the rest of the system from damage. - * The alternative would be to use a global variable that - * held the offset and refer to that variable each time we - * need a %gs variable (g). That approach would - * require an extra instruction and memory reference in - * every stack growth prolog and would also require - * rewriting the code that 8c generates for extern registers. - * - * Things get more disgusting on OS X 10.7 Lion. - * The 0x48 base mentioned above is the offset of the tsd - * array within the per-thread structure on Leopard and Snow Leopard. - * On Lion, the base moved a little, so while the math above - * still applies, the base is different. Thus, we cannot - * look for specific key values if we want to build binaries - * that run on both systems. Instead, forget about the - * specific key values and just allocate and initialize per-thread - * storage until we find a key that writes to the memory location - * we want. Then keep that key. - */ - ntofree = 0; - for(;;) { - if(pthread_key_create(&k, nil) != 0) { - fprintf(stderr, "runtime/cgo: pthread_key_create failed\n"); - abort(); - } - pthread_setspecific(k, (void*)magic1); - asm volatile("movl %%gs:0x468, %0" : "=r"(x)); - pthread_setspecific(k, 0); - if(x == magic1) { - k1 = k; - break; - } - if(ntofree >= nelem(tofree)) { - fprintf(stderr, "runtime/cgo: could not obtain pthread_keys\n"); - fprintf(stderr, "\ttried"); - for(i=0; istacklo = (uintptr)&attr - size + 4096; pthread_attr_destroy(&attr); - - inittls(); } @@ -142,10 +57,9 @@ threadentry(void *v) ts = *(ThreadStart*)v; free(v); - if (pthread_setspecific(k1, (void*)ts.g) != 0) { - fprintf(stderr, "runtime/cgo: pthread_setspecific failed\n"); - abort(); - } + // Move the g pointer into the slot reserved in thread local storage. + // Constant must match the one in cmd/link/internal/ld/sym.go. + asm volatile("movq %0, %%gs:0x18" :: "r"(ts.g)); crosscall_386(ts.fn); return nil; diff --git a/src/runtime/cgo/gcc_darwin_amd64.c b/src/runtime/cgo/gcc_darwin_amd64.c index c57608c675..51410d5026 100644 --- a/src/runtime/cgo/gcc_darwin_amd64.c +++ b/src/runtime/cgo/gcc_darwin_amd64.c @@ -9,60 +9,6 @@ #include "libcgo_unix.h" static void* threadentry(void*); -static pthread_key_t k1; - -#define magic1 (0x23581321345589ULL) - -static void -inittls(void) -{ - uint64 x; - pthread_key_t tofree[128], k; - int i, ntofree; - - /* - * Same logic, code as darwin_386.c:/inittls, except that words - * are 8 bytes long now, and the thread-local storage starts - * at 0x60 on Leopard / Snow Leopard. So the offset is - * 0x60+8*0x108 = 0x8a0. - * - * The linker and runtime hard-code this constant offset - * from %gs where we expect to find g. - * Known to src/cmd/link/internal/ld/sym.go:/0x8a0 - * and to src/runtime/sys_darwin_amd64.s:/0x8a0 - * - * As disgusting as on the 386; same justification. - */ - ntofree = 0; - for(;;) { - if(pthread_key_create(&k, nil) != 0) { - fprintf(stderr, "runtime/cgo: pthread_key_create failed\n"); - abort(); - } - pthread_setspecific(k, (void*)magic1); - asm volatile("movq %%gs:0x8a0, %0" : "=r"(x)); - pthread_setspecific(k, 0); - if(x == magic1) { - k1 = k; - break; - } - if(ntofree >= nelem(tofree)) { - fprintf(stderr, "runtime/cgo: could not obtain pthread_keys\n"); - fprintf(stderr, "\ttried"); - for(i=0; istacklo = (uintptr)&attr - size + 4096; pthread_attr_destroy(&attr); - - inittls(); } @@ -113,10 +57,9 @@ threadentry(void *v) ts = *(ThreadStart*)v; free(v); - if (pthread_setspecific(k1, (void*)ts.g) != 0) { - fprintf(stderr, "runtime/cgo: pthread_setspecific failed\n"); - abort(); - } + // Move the g pointer into the slot reserved in thread local storage. + // Constant must match the one in cmd/link/internal/ld/sym.go. + asm volatile("movq %0, %%gs:0x30" :: "r"(ts.g)); crosscall_amd64(ts.fn); return nil; diff --git a/src/runtime/sys_darwin_386.s b/src/runtime/sys_darwin_386.s index 3b5ed44724..3831ba5a79 100644 --- a/src/runtime/sys_darwin_386.s +++ b/src/runtime/sys_darwin_386.s @@ -525,15 +525,14 @@ TEXT runtime·setldt(SB),NOSPLIT,$32 * When linking against the system libraries, * we use its pthread_create and let it set up %gs * for us. When we do that, the private storage - * we get is not at 0(GS) but at 0x468(GS). - * 8l rewrites 0(TLS) into 0x468(GS) for us. + * we get is not at 0(GS) but at 0x18(GS). + * The linker rewrites 0(TLS) into 0x18(GS) for us. * To accommodate that rewrite, we translate the - * address and limit here so that 0x468(GS) maps to 0(address). + * address here so that 0x18(GS) maps to 0(address). * - * See cgo/gcc_darwin_386.c:/468 for the derivation - * of the constant. + * Constant must match the one in cmd/link/internal/ld/sym.go. */ - SUBL $0x468, BX + SUBL $0x18, BX /* * Must set up as USER_CTHREAD segment because diff --git a/src/runtime/sys_darwin_amd64.s b/src/runtime/sys_darwin_amd64.s index ab57843dfa..7a4f8ba39a 100644 --- a/src/runtime/sys_darwin_amd64.s +++ b/src/runtime/sys_darwin_amd64.s @@ -569,11 +569,10 @@ TEXT runtime·mach_semaphore_signal_all(SB),NOSPLIT,$0 // set tls base to DI TEXT runtime·settls(SB),NOSPLIT,$32 /* - * Same as in sys_darwin_386.s:/ugliness, different constant. - * See cgo/gcc_darwin_amd64.c for the derivation - * of the constant. - */ - SUBQ $0x8a0, DI + * Same as in sys_darwin_386.s, but a different constant. + * Constant must match the one in cmd/link/internal/ld/sym.go. + */ + SUBQ $0x30, DI MOVL $(0x3000000+3), AX // thread_fast_set_cthread_self - machdep call #3 SYSCALL