wasm2c: Add config macro and tests for disabling unused reads

Author: shravanrn

.github/workflows/build.yml

@@ -172,7 +172,7 @@ jobs:
     runs-on: ubuntu-latest
     env:
       USE_NINJA: "1"
-      WASM2C_CFLAGS: "-DWASM_RT_USE_MMAP=1 -DWASM_RT_SKIP_SIGNAL_RECOVERY=1 -DWASM_RT_NONCONFORMING_STACK_UNCHECKED=1 -DWASM2C_TEST_EMBEDDER_SIGNAL_HANDLING"
+      WASM2C_CFLAGS: "-DWASM_RT_USE_MMAP=1 -DWASM_RT_SKIP_SIGNAL_RECOVERY=1 -DWASM_RT_NONCONFORMING_STACK_UNCHECKED=1 -DWASM_RT_NONCONFORMING_DISABLE_FORCE_READ=1 -DWASM2C_TEST_EMBEDDER_SIGNAL_HANDLING"
     steps:
     - uses: actions/setup-python@v1
       with:
@@ -182,5 +182,5 @@ jobs:
         submodules: true
     - run: sudo apt-get install ninja-build
     - run: make clang-debug
-    - name: tests (wasm2c tests excluding memory64 and stack exhaustion)
-      run: ./test/run-tests.py *wasm2c* --exclude memory64 --exclude call.txt --exclude call_indirect.txt --exclude fac.txt --exclude skip-stack-guard-page.txt
+    - name: tests (wasm2c tests excluding memory64, stack exhaustion, and unused read elimination)
+      run: ./test/run-tests.py *wasm2c* --exclude memory64 --exclude call.txt --exclude call_indirect.txt --exclude fac.txt --exclude skip-stack-guard-page.txt --exclude address-overflow.txt --exclude address.txt --exclude address0.txt --exclude address1.txt --exclude traps.txt --exclude traps0.txt --exclude simd_address.txt

src/prebuilt/wasm2c_simd_source_declarations.cc

@@ -1,4 +1,6 @@
-const char* s_simd_source_declarations = R"w2c_template(#if defined(__GNUC__) && defined(__x86_64__)
+const char* s_simd_source_declarations = R"w2c_template(#if defined(__GNUC__) && defined(__x86_64__) && \
+)w2c_template"
+R"w2c_template(    !WASM_RT_NONCONFORMING_DISABLE_FORCE_READ
 )w2c_template"
 R"w2c_template(#define SIMD_FORCE_READ(var) __asm__("" ::"x"(var));
 )w2c_template"

src/prebuilt/wasm2c_source_declarations.cc

@@ -135,7 +135,7 @@ R"w2c_template(#define MEMCHECK(mem, a, t) RANGE_CHECK(mem, a, sizeof(t))
 R"w2c_template(#endif
 )w2c_template"
 R"w2c_template(
-#ifdef __GNUC__
+#if defined(__GNUC__) && !WASM_RT_NONCONFORMING_DISABLE_FORCE_READ
 )w2c_template"
 R"w2c_template(#define FORCE_READ_INT(var) __asm__("" ::"r"(var));
 )w2c_template"

src/template/wasm2c.declarations.c

@@ -73,7 +73,7 @@ static inline bool func_types_eq(const wasm_rt_func_type_t a,
 #define MEMCHECK(mem, a, t) RANGE_CHECK(mem, a, sizeof(t))
 #endif
 
-#ifdef __GNUC__
+#if defined(__GNUC__) && !WASM_RT_NONCONFORMING_DISABLE_FORCE_READ
 #define FORCE_READ_INT(var) __asm__("" ::"r"(var));
 // Clang on Mips requires "f" constraints on floats
 // See https://github.com/llvm/llvm-project/issues/64241

src/template/wasm2c_simd.declarations.c

@@ -1,4 +1,5 @@
-#if defined(__GNUC__) && defined(__x86_64__)
+#if defined(__GNUC__) && defined(__x86_64__) && \
+    !WASM_RT_NONCONFORMING_DISABLE_FORCE_READ
 #define SIMD_FORCE_READ(var) __asm__("" ::"x"(var));
 #else
 #define SIMD_FORCE_READ(var)

test/wasm2c/add.txt

@@ -140,7 +140,7 @@ static inline bool func_types_eq(const wasm_rt_func_type_t a,
 #define MEMCHECK(mem, a, t) RANGE_CHECK(mem, a, sizeof(t))
 #endif
 
-#ifdef __GNUC__
+#if defined(__GNUC__) && !WASM_RT_NONCONFORMING_DISABLE_FORCE_READ
 #define FORCE_READ_INT(var) __asm__("" ::"r"(var));
 // Clang on Mips requires "f" constraints on floats
 // See https://github.com/llvm/llvm-project/issues/64241

test/wasm2c/check-imports.txt

@@ -163,7 +163,7 @@ static inline bool func_types_eq(const wasm_rt_func_type_t a,
 #define MEMCHECK(mem, a, t) RANGE_CHECK(mem, a, sizeof(t))
 #endif
 
-#ifdef __GNUC__
+#if defined(__GNUC__) && !WASM_RT_NONCONFORMING_DISABLE_FORCE_READ
 #define FORCE_READ_INT(var) __asm__("" ::"r"(var));
 // Clang on Mips requires "f" constraints on floats
 // See https://github.com/llvm/llvm-project/issues/64241

test/wasm2c/export-names.txt

@@ -163,7 +163,7 @@ static inline bool func_types_eq(const wasm_rt_func_type_t a,
 #define MEMCHECK(mem, a, t) RANGE_CHECK(mem, a, sizeof(t))
 #endif
 
-#ifdef __GNUC__
+#if defined(__GNUC__) && !WASM_RT_NONCONFORMING_DISABLE_FORCE_READ
 #define FORCE_READ_INT(var) __asm__("" ::"r"(var));
 // Clang on Mips requires "f" constraints on floats
 // See https://github.com/llvm/llvm-project/issues/64241

test/wasm2c/hello.txt

@@ -171,7 +171,7 @@ static inline bool func_types_eq(const wasm_rt_func_type_t a,
 #define MEMCHECK(mem, a, t) RANGE_CHECK(mem, a, sizeof(t))
 #endif
 
-#ifdef __GNUC__
+#if defined(__GNUC__) && !WASM_RT_NONCONFORMING_DISABLE_FORCE_READ
 #define FORCE_READ_INT(var) __asm__("" ::"r"(var));
 // Clang on Mips requires "f" constraints on floats
 // See https://github.com/llvm/llvm-project/issues/64241

test/wasm2c/minimal.txt

@@ -134,7 +134,7 @@ static inline bool func_types_eq(const wasm_rt_func_type_t a,
 #define MEMCHECK(mem, a, t) RANGE_CHECK(mem, a, sizeof(t))
 #endif
 
-#ifdef __GNUC__
+#if defined(__GNUC__) && !WASM_RT_NONCONFORMING_DISABLE_FORCE_READ
 #define FORCE_READ_INT(var) __asm__("" ::"r"(var));
 // Clang on Mips requires "f" constraints on floats
 // See https://github.com/llvm/llvm-project/issues/64241

test/wasm2c/tail-calls.txt

@@ -164,7 +164,7 @@ static inline bool func_types_eq(const wasm_rt_func_type_t a,
 #define MEMCHECK(mem, a, t) RANGE_CHECK(mem, a, sizeof(t))
 #endif
 
-#ifdef __GNUC__
+#if defined(__GNUC__) && !WASM_RT_NONCONFORMING_DISABLE_FORCE_READ
 #define FORCE_READ_INT(var) __asm__("" ::"r"(var));
 // Clang on Mips requires "f" constraints on floats
 // See https://github.com/llvm/llvm-project/issues/64241

wasm2c/wasm-rt.h

@@ -174,6 +174,16 @@ extern "C" {
 #define WASM_RT_NONCONFORMING_STACK_UNCHECKED 0
 #endif
 
+/* This macro, if defined, allows the embedder to specify that wasm2c can remove
+ * linear memory reads which are unused. Normally, Wasm requires does not allow
+ * reads to be eliminated when using guard pages, as OOB reads must still trap.
+ * This a non conformant configuration, i.e., this does not respect Wasm's
+ * specification. Use with caution.
+ */
+#ifndef WASM_RT_NONCONFORMING_DISABLE_FORCE_READ
+#define WASM_RT_NONCONFORMING_DISABLE_FORCE_READ 0
+#endif
+
 /* We need to detect and trap stack overflows. If we use a signal handler on
  * POSIX systems, this can detect call stack overflows. On windows, or platforms
  * without a signal handler, we use stack depth counting. */