1. For %fs/fsbase the patch follows the macOS logic with LDT descriptor registration and Linux with switching. One notable difference is that on 32->64 transition we set %fs to GSEL(GUFS32_SEL, SEL_UPL) before restoring fsbase, otherwise FreeBSD will just revert it by reloading the selector [at the first opportunity](https://github.com/freebsd/freebsd-src/blob/5673462af5330df20733008beae48a24...). GSEL(GUFS32_SEL, SEL_UPL) is the default %fs value on FreeBSD and is special-cased to save/restore actual fsbase value to/from PCB. 2. I was told we could get rid of fsbase glitches in signal handlers by blocking signals with [sigfastblock(2)](https://man.freebsd.org/cgi/man.cgi?query=sigfastblock) between %fs reset to the default value and fsbase reset to pthread_teb. This is currently a part of internal API for libthr, which could be exposed as pthread_signal_block_np for Wine. I'm on the fence whether it's worth it. 3. I fully admit I have no idea what registers are worth preserving around fallback sysarch(AMD64_SET_FSBASE) syscalls and whether it's appropriate to push those registers to stack. ("Kernel" stack should be fine, I assume?) Syscalls definitely clobber r8-r11. 4. For %ss see https://lkml.org/lkml/2015/4/24/216. FreeBSD doesn't have a similar workaround in the kernel, so it goes into Wine.
-- v7: ntdll: Work around AMD SYSRET SS descriptor behavior on FreeBSD. ntdll: Unbreak new wow64 mode on FreeBSD.
From: Alexander Shaikhulin iwtcex@gmail.com
--- dlls/ntdll/unix/signal_x86_64.c | 137 ++++++++++++++++++++++++++++++-- 1 file changed, 132 insertions(+), 5 deletions(-)
diff --git a/dlls/ntdll/unix/signal_x86_64.c b/dlls/ntdll/unix/signal_x86_64.c index dc07c1778ea..7bb41b7910a 100644 --- a/dlls/ntdll/unix/signal_x86_64.c +++ b/dlls/ntdll/unix/signal_x86_64.c @@ -152,6 +152,9 @@ __ASM_GLOBAL_FUNC( alloc_fs_sel,
#elif defined(__FreeBSD__) || defined (__FreeBSD_kernel__)
+#include <machine/cpufunc.h> +#include <machine/segments.h> +#include <machine/specialreg.h> #include <machine/trap.h>
#define RAX_sig(context) ((context)->uc_mcontext.mc_rax) @@ -469,7 +472,7 @@ static inline struct amd64_thread_data *amd64_thread_data(void) return (struct amd64_thread_data *)ntdll_get_thread_data()->cpu_data; }
-#if defined(__linux__) || defined(__APPLE__) +#if defined(__linux__) || defined(__APPLE__) || defined(__FreeBSD__) static inline TEB *get_current_teb(void) { unsigned long rsp; @@ -1654,7 +1657,7 @@ __ASM_GLOBAL_FUNC( call_user_mode_callback, "movq %r15,%rcx\n" /* func */ /* switch to user stack */ "1:\tmovq %rdi,%rsp\n\t" /* user_rsp */ -#ifdef __linux__ +#if defined(__linux__) || defined(__FreeBSD__) "testl $4,%r14d\n\t" /* SYSCALL_HAVE_PTHREAD_TEB */ "jz 1f\n\t" "movw 0x338(%r13),%fs\n" /* amd64_thread_data()->fs */ @@ -2375,6 +2378,16 @@ static void ldt_set_entry( WORD sel, LDT_ENTRY entry )
#if defined(__APPLE__) if (i386_set_ldt(index, (union ldt_entry *)&entry, 1) < 0) perror("i386_set_ldt"); +#elif defined(__FreeBSD__) + struct i386_ldt_args p; + p.start = index; + p.descs = (struct user_segment_descriptor *)&entry; + p.num = 1; + if (sysarch(I386_SET_LDT, &p) == -1) + { + perror("i386_set_ldt"); + exit(1); + } #else fprintf( stderr, "No LDT support on this platform\n" ); exit(1); @@ -2485,6 +2498,38 @@ static void *mac_thread_gsbase(void) } #endif
+#ifdef __FreeBSD__ +static __siginfohandler_t *libthr_signal_handlers[_SIG_MAXSIG]; + +/* occasionally signals happen right between %fs reset to GUFS32_SEL and fsbase correction, +which results in fsbase being wrong on handler entry; we'll just restore fsbase ourselves */ +static void libthr_sighandler_wrapper(int sig, siginfo_t *info, void *_ucp) { + struct ntdll_thread_data *thread_data = (struct ntdll_thread_data *)&get_current_teb()->GdiTebBatch; + amd64_set_fsbase(((struct amd64_thread_data *)thread_data->cpu_data)->pthread_teb); + libthr_signal_handlers[sig - 1](sig, info, _ucp); +} + +extern int __sys_sigaction(int, const struct sigaction *, struct sigaction *); + +static int wrap_libthr_signal_handlers(void) { + struct sigaction act; + int sig; + + for (sig = 1; sig <= _SIG_MAXSIG; sig++) { + + if (__sys_sigaction(sig, NULL, &act) == -1) return -1; + if (act.sa_sigaction != NULL) { + + libthr_signal_handlers[sig - 1] = act.sa_sigaction; + act.sa_sigaction = libthr_sighandler_wrapper; + + if (__sys_sigaction(sig, &act, NULL) == -1) return -1; + } + } + + return 0; +} +#endif
/********************************************************************** * signal_init_process @@ -2550,6 +2595,37 @@ void signal_init_process(void) break; } } +#elif defined(__FreeBSD__) + if (wow_teb) + { + u_int p[4]; + u_int cpu_stdext_feature; + + LDT_ENTRY fs32_entry = ldt_make_entry(wow_teb, page_size - 1, LDT_FLAGS_DATA | LDT_FLAGS_32BIT); + + cs32_sel = GSEL(GUCODE32_SEL, SEL_UPL); + + amd64_thread_data()->fs = LSEL(first_ldt_entry, SEL_UPL); + ldt_set_entry(amd64_thread_data()->fs, fs32_entry); + + syscall_flags |= SYSCALL_HAVE_PTHREAD_TEB; + + do_cpuid(0, p); + if (p[0] >= 7) + { + cpuid_count(7, 0, p); + cpu_stdext_feature = p[1]; + } + else + { + cpu_stdext_feature = 0; + } + + if (cpu_stdext_feature & CPUID_STDEXT_FSGSBASE) + { + syscall_flags |= SYSCALL_HAVE_WRFSGSBASE; + } + } #endif
sig_act.sa_mask = server_block_set; @@ -2574,6 +2650,9 @@ void signal_init_process(void) #ifdef __APPLE__ sig_act.sa_sigaction = sigsys_handler; if (sigaction( SIGSYS, &sig_act, NULL ) == -1) goto error; +#endif +#ifdef __FreeBSD__ + if (wrap_libthr_signal_handlers() == -1) goto error; #endif return;
@@ -2603,7 +2682,8 @@ void init_syscall_frame( LPTHREAD_START_ROUTINE entry, void *arg, BOOL suspend, arch_prctl( ARCH_GET_FS, &thread_data->pthread_teb ); if (fs32_sel) alloc_fs_sel( fs32_sel >> 3, get_wow_teb( teb )); #elif defined (__FreeBSD__) || defined (__FreeBSD_kernel__) - amd64_set_gsbase( teb ); + amd64_set_gsbase(teb); + amd64_get_fsbase(&thread_data->pthread_teb); #elif defined(__NetBSD__) sysarch( X86_64_SET_GSBASE, &teb ); #elif defined (__APPLE__) @@ -2818,6 +2898,30 @@ __ASM_GLOBAL_FUNC( __wine_syscall_dispatcher, "syscall\n\t" "leaq -0x98(%rbp),%rcx\n" "2:\n\t" +#elif defined(__FreeBSD__) + "testl $4,%r14d\n\t" /* SYSCALL_HAVE_PTHREAD_TEB */ + "jz 2f\n\t" + "movq $0x13,%rsi\n\t" /* GSEL(GUFS32_SEL, SEL_UPL) */ + "movq %rsi,%fs\n\t" + "movq 0x320(%r13),%rsi\n\t" /* amd64_thread_data()->pthread_teb */ + "testl $8,%r14d\n\t" /* SYSCALL_HAVE_WRFSGSBASE */ + "jz 1f\n\t" + "wrfsbase %rsi\n\t" + "jmp 2f\n" + "1:\n\t" + "pushq %r8\n\t" + "pushq %r9\n\t" + "pushq %r10\n\t" + "pushq %r11\n\t" + "movq $0xa5,%rax\n\t" /* sysarch */ + "movq $0x81,%rdi\n\t" /* AMD64_SET_FSBASE */ + "syscall\n\t" + "popq %r11\n\t" + "popq %r10\n\t" + "popq %r9\n\t" + "popq %r8\n\t" + "leaq -0x98(%rbp),%rcx\n" + "2:\n\t" #elif defined __APPLE__ "movq 0x320(%r13),%rdi\n\t" /* amd64_thread_data()->pthread_teb */ "xorl %esi,%esi\n\t" @@ -2863,7 +2967,7 @@ __ASM_GLOBAL_FUNC( __wine_syscall_dispatcher, __ASM_CFI(".cfi_remember_state\n\t") __ASM_CFI_CFA_IS_AT2(rcx, 0xa8, 0x01) /* frame->syscall_cfa */ "leaq 0x70(%rcx),%rsp\n\t" /* %rsp > frame means no longer inside syscall */ -#ifdef __linux__ +#if defined(__linux__) || defined(__FreeBSD__) "testl $4,%r14d\n\t" /* SYSCALL_HAVE_PTHREAD_TEB */ "jz 1f\n\t" "movw 0x338(%r13),%fs\n" /* amd64_thread_data()->fs */ @@ -3103,6 +3207,29 @@ __ASM_GLOBAL_FUNC( __wine_unix_call_dispatcher, "mov $158,%eax\n\t" /* SYS_arch_prctl */ "syscall\n\t" "2:\n\t" +#elif defined(__FreeBSD__) + "testl $4,%r14d\n\t" /* SYSCALL_HAVE_PTHREAD_TEB */ + "jz 2f\n\t" + "movq $0x13,%rsi\n\t" /* GSEL(GUFS32_SEL, SEL_UPL) */ + "movq %rsi,%fs\n\t" + "movq 0x320(%r13),%rsi\n\t" /* amd64_thread_data()->pthread_teb */ + "testl $8,%r14d\n\t" /* SYSCALL_HAVE_WRFSGSBASE */ + "jz 1f\n\t" + "wrfsbase %rsi\n\t" + "jmp 2f\n" + "1:\n\t" + "pushq %r8\n\t" + "pushq %r9\n\t" + "pushq %r10\n\t" + "pushq %r11\n\t" + "movq $0xa5,%rax\n\t" /* sysarch */ + "movq $0x81,%rdi\n\t" /* AMD64_SET_FSBASE */ + "syscall\n\t" + "popq %r11\n\t" + "popq %r10\n\t" + "popq %r9\n\t" + "popq %r8\n\t" + "2:\n\t" #elif defined __APPLE__ "movq 0x320(%r13),%rdi\n\t" /* amd64_thread_data()->pthread_teb */ "xorl %esi,%esi\n\t" @@ -3127,7 +3254,7 @@ __ASM_GLOBAL_FUNC( __wine_unix_call_dispatcher, /* switch to user stack */ "movq 0x88(%rcx),%rsp\n\t" __ASM_CFI(".cfi_restore_state\n\t") -#ifdef __linux__ +#if defined(__linux__) || defined(__FreeBSD__) "testl $4,%r14d\n\t" /* SYSCALL_HAVE_PTHREAD_TEB */ "jz 1f\n\t" "movw 0x338(%r13),%fs\n" /* amd64_thread_data()->fs */
From: Alexander Shaikhulin iwtcex@gmail.com
On AMD CPUs the cached SS descriptor attributes could be invalid after return to the userspace with SYSRET, which doesn't matter in the long mode, but would easily crash programs in the compatibility mode. Reloading %ss avoids that.
Note that Linux already has X86_BUG_SYSRET_SS_ATTRS as the workaround for this issue. --- dlls/ntdll/unix/signal_x86_64.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
diff --git a/dlls/ntdll/unix/signal_x86_64.c b/dlls/ntdll/unix/signal_x86_64.c index 7bb41b7910a..9354d4645b1 100644 --- a/dlls/ntdll/unix/signal_x86_64.c +++ b/dlls/ntdll/unix/signal_x86_64.c @@ -2971,6 +2971,11 @@ __ASM_GLOBAL_FUNC( __wine_syscall_dispatcher, "testl $4,%r14d\n\t" /* SYSCALL_HAVE_PTHREAD_TEB */ "jz 1f\n\t" "movw 0x338(%r13),%fs\n" /* amd64_thread_data()->fs */ +# ifdef __FreeBSD__ + /* reset %ss (after sysret) for AMD */ + "movq $0x3b,%rsi\n\t" /* GSEL(GUDATA_SEL, SEL_UPL) */ + "movq %rsi,%ss\n\t" +# endif "1:\n\t" #elif defined __APPLE__ "movq %rax,%r8\n\t" @@ -3258,6 +3263,11 @@ __ASM_GLOBAL_FUNC( __wine_unix_call_dispatcher, "testl $4,%r14d\n\t" /* SYSCALL_HAVE_PTHREAD_TEB */ "jz 1f\n\t" "movw 0x338(%r13),%fs\n" /* amd64_thread_data()->fs */ +# ifdef __FreeBSD__ + /* reset %ss (after sysret) for AMD */ + "movq $0x3b,%rsi\n\t" /* GSEL(GUDATA_SEL, SEL_UPL) */ + "movq %rsi,%ss\n\t" +# endif "1:\n\t" #elif defined __APPLE__ "movq %rax,%rdx\n\t"
On Thu May 22 23:42:18 2025 +0000, Alexander Shaikhulin wrote:
This is the most concise explanation that I found: https://github.com/torvalds/linux/blob/a11a72229881d8ac1d52ea727101bc9c74418....
I split that part into a separate commit with a more elaborate message. Let me know if it's still unclear.
On Fri May 23 06:53:04 2025 +0000, Alexander Shaikhulin wrote:
I split that part into a separate commit with a more elaborate message. Let me know if it's still unclear.
Thanks. It does sound like something that should be fixed in the kernel.
On Fri May 23 05:40:37 2025 +0000, Alexander Shaikhulin wrote:
As far as I understand it, libc's sigaction is normally being redirected to __thr_sigaction, which wraps every signal handler, that [wrapper](https://github.com/freebsd/freebsd-src/blob/3c3dd62966123b424657983d9a4d173f...) relies on TLS. Thus it's too late to set fsbase in init_handler. (Also FreeBSD will do leave_handler's job itself, no need to worry about that one.) This is still a bit obnoxious and we are actually discussing getting rid of that particular annoyance on the FreeBSD side. Would take some time, though.
Are these wrappers needed for our case? Couldn't you install the handlers directly with the kernel?
On Fri May 23 07:37:46 2025 +0000, Alexandre Julliard wrote:
Are these wrappers needed for our case? Couldn't you install the handlers directly with the kernel?
I'd rather not play a lottery with libthr internals: at least a few FreeBSD devs thought those wrappers are useful for something, these people are still around and they know where I live :)
The current plan is simply modifying libthr to communicate the proper tls base value to the kernel (https://reviews.freebsd.org/D50482 and related patches), which would make that part of the merge request completely unnecessary in 6-10 months.
I don't have an opinion on what to do until that, to be honest.
On Fri May 23 06:53:04 2025 +0000, Alexandre Julliard wrote:
Thanks. It does sound like something that should be fixed in the kernel.
On the other hand, I'm still amazed Linux somehow managed to hit that. The effect is only visible on FreeBSD in wow64 Wine and this could be argued either way.
On Sat May 24 01:54:50 2025 +0000, Alexander Shaikhulin wrote:
I'd rather not play a lottery with libthr internals: at least a few FreeBSD devs thought those wrappers are useful for something, these people are still around and they know where I live :) The current plan is to modify libthr to communicate the proper tls base value to the kernel (https://reviews.freebsd.org/D50482 and related patches), which would make that part of the merge request completely unnecessary in 6-10 months. I don't have an opinion on what to do until that, to be honest.
I suppose I could drop libthr_sighandler_wrapper and annoy @gerald with a yet another local patch instead (until the fix propagates to all supported FreeBSD releases). Would that be acceptable?
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Alexander Shaikhulin -
Alexander Shaikhulin (＠shkhln)
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Alexandre Julliard (＠julliard)