From c6853eb4857908072fd1d7c28dffb1d2613a0ee6 Mon Sep 17 00:00:00 2001 From: Shravan Narayan Date: Mon, 15 Jul 2024 17:06:24 -0500 Subject: wasm2c: Segue support for CPUs without wrgsbase instructions --- wasm2c/examples/fac/fac.c | 76 ++++++++++++++++++++++++++++++++--------------- wasm2c/wasm-rt-impl.c | 39 ++++++++++++++++++++++++ wasm2c/wasm-rt.h | 21 +++++++++++++ 3 files changed, 112 insertions(+), 24 deletions(-) (limited to 'wasm2c') diff --git a/wasm2c/examples/fac/fac.c b/wasm2c/examples/fac/fac.c index d9f821df..e253cc2a 100644 --- a/wasm2c/examples/fac/fac.c +++ b/wasm2c/examples/fac/fac.c @@ -47,14 +47,15 @@ // (1) Segue is allowed using WASM_RT_ALLOW_SEGUE // (2) on x86_64 without WABT_BIG_ENDIAN enabled // (3) the Wasm module uses a single unshared imported or exported memory -// (4) the compiler supports: intrinsics for (rd|wr)(fs|gs)base, "address -// namespaces" for accessing pointers, and supports memcpy on pointers with -// custom "address namespaces". GCC does not support the memcpy requirement, -// so this leaves only clang for now. -#if WASM_RT_ALLOW_SEGUE && !WABT_BIG_ENDIAN && \ - (defined(__x86_64__) || defined(_M_X64)) && \ - WASM_RT_MODULE_IS_SINGLE_UNSHARED_MEMORY && __clang__ && \ - __has_builtin(__builtin_ia32_wrgsbase64) +// (4) the compiler supports: intrinsics for (rd|wr)gsbase, "address namespaces" +// for accessing pointers, and supports memcpy on pointers with custom +// "address namespaces". GCC does not support the memcpy requirement, so +// this leaves only clang for now. +// (5) The OS doesn't replace the segment register on context switch which +// eliminates windows for now +#if WASM_RT_ALLOW_SEGUE && !WABT_BIG_ENDIAN && \ + (defined(__x86_64__) || defined(_M_X64)) && IS_SINGLE_UNSHARED_MEMORY && \ + __clang__ && __has_builtin(__builtin_ia32_wrgsbase64) && !defined(_WIN32) #define WASM_RT_USE_SEGUE 1 #else #define WASM_RT_USE_SEGUE 0 @@ -62,21 +63,35 @@ #endif #if WASM_RT_USE_SEGUE -// Different segments are free on different platforms -// Windows uses GS for TLS, FS is free -// Linux uses FS for TLS, GS is free -#if defined(__WIN32) -#define WASM_RT_SEGUE_READ_BASE() __builtin_ia32_rdfsbase64() -#define WASM_RT_SEGUE_WRITE_BASE(base) \ - __builtin_ia32_wrfsbase64((uintptr_t)base) -#define MEM_ADDR_MEMOP(mem, addr, n) ((uint8_t __seg_fs*)(uintptr_t)addr) -#else -// POSIX style OS -#define WASM_RT_SEGUE_READ_BASE() __builtin_ia32_rdgsbase64() -#define WASM_RT_SEGUE_WRITE_BASE(base) \ - __builtin_ia32_wrgsbase64((uintptr_t)base) +// POSIX uses FS for TLS, GS is free +#include +#include +#include +#include + +static inline void* wasm_rt_segue_read_base() { + if (wasm_rt_fsgsbase_inst_supported) { + return (void*)__builtin_ia32_rdgsbase64(); + } else { + void* base; + if (syscall(SYS_arch_prctl, ARCH_GET_GS, &base) != 0) { + perror("Syscall SYS_arch_prctl error"); + abort(); + } + return base; + } +} +static inline void wasm_rt_segue_write_base(void* base) { + if (wasm_rt_fsgsbase_inst_supported) { + __builtin_ia32_wrgsbase64((uintptr_t)base); + } else { + if (syscall(SYS_arch_prctl, ARCH_SET_GS, (uintptr_t)base) != 0) { + perror("Syscall SYS_arch_prctl error"); + abort(); + } + } +} #define MEM_ADDR_MEMOP(mem, addr, n) ((uint8_t __seg_gs*)(uintptr_t)addr) -#endif #else #define MEM_ADDR_MEMOP(mem, addr, n) MEM_ADDR(mem, addr, n) #endif @@ -128,10 +143,23 @@ static inline bool func_types_eq(const wasm_rt_func_type_t a, TRAP(OOB); #endif +#if WASM_RT_USE_SEGUE && WASM_RT_SANITY_CHECKS +#include +#define WASM_RT_CHECK_BASE(mem) \ + if (((uintptr_t)((mem)->data)) != ((uintptr_t)wasm_rt_segue_read_base())) { \ + puts("Segment register mismatch\n"); \ + abort(); \ + } +#else +#define WASM_RT_CHECK_BASE(mem) +#endif + #if WASM_RT_MEMCHECK_GUARD_PAGES -#define MEMCHECK(mem, a, t) +#define MEMCHECK(mem, a, t) WASM_RT_CHECK_BASE(mem); #else -#define MEMCHECK(mem, a, t) RANGE_CHECK(mem, a, sizeof(t)) +#define MEMCHECK(mem, a, t) \ + WASM_RT_CHECK_BASE(mem); \ + RANGE_CHECK(mem, a, sizeof(t)) #endif #ifdef __GNUC__ diff --git a/wasm2c/wasm-rt-impl.c b/wasm2c/wasm-rt-impl.c index 52a42e85..851a4c5a 100644 --- a/wasm2c/wasm-rt-impl.c +++ b/wasm2c/wasm-rt-impl.c @@ -49,6 +49,19 @@ static void* g_sig_handler_handle = 0; #endif #endif +#if WASM_RT_USE_SEGUE || WASM_RT_ALLOW_SEGUE +// Currently Segue is used only for linux +#include +#ifdef __GLIBC__ +#include +#endif +bool wasm_rt_fsgsbase_inst_supported = false; + +#include // For ARCH_SET_GS +#include // For SYS_arch_prctl +#include // For syscall +#endif + #if WASM_RT_STACK_DEPTH_COUNT WASM_RT_THREAD_LOCAL uint32_t wasm_rt_call_stack_depth; WASM_RT_THREAD_LOCAL uint32_t wasm_rt_saved_call_stack_depth; @@ -220,6 +233,15 @@ void wasm_rt_init(void) { os_install_signal_handler(); } #endif + +#if WASM_RT_USE_SEGUE || WASM_RT_ALLOW_SEGUE +#if defined(__GLIBC__) && __GLIBC__ >= 2 && __GLIBC_MINOR__ >= 18 + // Check for support for userspace wrgsbase instructions + unsigned long val = getauxval(AT_HWCAP2); + wasm_rt_fsgsbase_inst_supported = val & (1 << 1); +#endif +#endif + assert(wasm_rt_is_initialized()); } @@ -257,6 +279,23 @@ void wasm_rt_free_thread(void) { #endif } +#if WASM_RT_USE_SEGUE || WASM_RT_ALLOW_SEGUE +void wasm_rt_syscall_set_segue_base(void* base) { + if (syscall(SYS_arch_prctl, ARCH_SET_GS, base) != 0) { + perror("wasm_rt_syscall_set_segue_base error"); + abort(); + } +} +void* wasm_rt_syscall_get_segue_base() { + void* base; + if (syscall(SYS_arch_prctl, ARCH_GET_GS, &base) != 0) { + perror("wasm_rt_syscall_get_segue_base error"); + abort(); + } + return base; +} +#endif + // Include table operations for funcref #define WASM_RT_TABLE_OPS_FUNCREF #include "wasm-rt-impl-tableops.inc" diff --git a/wasm2c/wasm-rt.h b/wasm2c/wasm-rt.h index 5c07ff44..c489c850 100644 --- a/wasm2c/wasm-rt.h +++ b/wasm2c/wasm-rt.h @@ -294,6 +294,27 @@ extern WASM_RT_THREAD_LOCAL uint32_t wasm_rt_call_stack_depth; #endif +#if WASM_RT_USE_SEGUE || WASM_RT_ALLOW_SEGUE +/** + * The segue optimization uses x86 segments to point to a linear memory. If + * used, the runtime must query whether it can use the fast userspace wrgsbase + * instructions or whether it must invoke syscalls to set the segment base, + * depending on the supported CPU features. The result of this query is saved in + * this variable. + */ +extern bool wasm_rt_fsgsbase_inst_supported; +/** + * If fast userspace wrgsbase instructions don't exist, the runtime most provide + * a function that invokes the OS' underlying syscall to set the segment base. + */ +void wasm_rt_syscall_set_segue_base(void* base); +/** + * If fast userspace rdgsbase instructions don't exist, the runtime most provide + * a function that invokes the OS' underlying syscall to get the segment base. + */ +void* wasm_rt_syscall_get_segue_base(); +#endif + #if defined(_MSC_VER) #define WASM_RT_NO_RETURN __declspec(noreturn) #else -- cgit v1.2.3