diff options
Diffstat (limited to 'wasm2c/wasm-rt.h')
| -rw-r--r-- | wasm2c/wasm-rt.h | 29 |
1 files changed, 28 insertions, 1 deletions
diff --git a/wasm2c/wasm-rt.h b/wasm2c/wasm-rt.h index b72d12df..3274a15d 100644 --- a/wasm2c/wasm-rt.h +++ b/wasm2c/wasm-rt.h @@ -228,6 +228,33 @@ extern "C" { #define WASM_RT_SEGUE_FREE_SEGMENT 0 #endif +#ifndef WASM_RT_USE_SEGUE +// Memory functions can use the segue optimization if allowed. The segue +// optimization uses x86 segments to point to a linear memory. We use this +// optimization when: +// +// (1) Segue is allowed using WASM_RT_ALLOW_SEGUE +// (2) on x86_64 without WABT_BIG_ENDIAN enabled +// (3) 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. +// (4) The OS provides a way to query if (rd|wr)gsbase is allowed by the kernel +// or the implementation has to use a syscall for this. +// (5) The OS doesn't replace the segment register on context switch which +// eliminates windows for now +// +// While more OS can be supported in the future, we only support linux for now +#if WASM_RT_ALLOW_SEGUE && !WABT_BIG_ENDIAN && \ + (defined(__x86_64__) || defined(_M_X64)) && __clang__ && \ + __has_builtin(__builtin_ia32_wrgsbase64) && !defined(_WIN32) && \ + defined(__linux__) +#define WASM_RT_USE_SEGUE 1 +#else +#define WASM_RT_USE_SEGUE 0 +#endif +#endif + /** * This macro, if defined, allows the embedder to disable all stack exhaustion * checks. This a non conformant configuration, i.e., this does not respect @@ -306,7 +333,7 @@ extern WASM_RT_THREAD_LOCAL uint32_t wasm_rt_call_stack_depth; #endif -#if WASM_RT_USE_SEGUE || WASM_RT_ALLOW_SEGUE +#if WASM_RT_USE_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 |