cppgc: Support GCC for conservative stack scan

Assumes that (is_clang = false && !is_win) => GCC or other compiler with
inline assembly that is gas-compatible.

Bug: chromium:1056170
Change-Id: I1a2a2d13b7d4af630349d9194b64394c9736ad3c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2137405Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67014}

BUILD.gn

@@ -348,7 +348,9 @@ config("libbase_config") {
 
 # This config should be applied to code using the cppgc_base.
 config("cppgc_base_config") {
-  if (is_clang) {
+  # Assume is_clang = false means GCC or other compilers that are compatible
+  # with gas inline assembly on non-Windows builds.
+  if (is_clang || !is_win) {
     if (target_cpu == "x64" || target_cpu == "x86" || target_cpu == "arm") {
       defines = [ "CPPGC_SUPPORTS_CONSERVATIVE_STACK_SCAN" ]
     }
@@ -3967,13 +3969,13 @@ v8_source_set("cppgc_base") {
     "src/heap/cppgc/stack.h",
   ]
 
-  if (is_clang) {
+  if (is_clang || !is_win) {
     if (target_cpu == "x64") {
-      sources += [ "src/heap/cppgc/asm/x64/push_registers_clang.cc" ]
+      sources += [ "src/heap/cppgc/asm/x64/push_registers_asm.cc" ]
     } else if (target_cpu == "x86") {
-      sources += [ "src/heap/cppgc/asm/ia32/push_registers_clang.cc" ]
+      sources += [ "src/heap/cppgc/asm/ia32/push_registers_asm.cc" ]
     } else if (target_cpu == "arm") {
-      sources += [ "src/heap/cppgc/asm/arm/push_registers_clang.cc" ]
+      sources += [ "src/heap/cppgc/asm/arm/push_registers_asm.cc" ]
     }
   }
 

src/heap/cppgc/asm/x64/push_registers_clang.cc → src/heap/cppgc/asm/x64/push_registers_asm.cc

@@ -18,10 +18,10 @@
 // Otherwise, undefined.
 #ifdef _WIN64
 
-  // We maintain 16-byte alignment at calls. There is an 8-byte return address
-  // on the stack and we push 72 bytes which maintains 16-byte stack alignment
-  // at the call.
-  // Source: https://docs.microsoft.com/en-us/cpp/build/x64-calling-convention
+// We maintain 16-byte alignment at calls. There is an 8-byte return address
+// on the stack and we push 72 bytes which maintains 16-byte stack alignment
+// at the call.
+// Source: https://docs.microsoft.com/en-us/cpp/build/x64-calling-convention
 asm(".globl PushAllRegistersAndIterateStack             \n"
     "PushAllRegistersAndIterateStack:                   \n"
     // rbp is callee-saved. Maintain proper frame pointer for debugging.
@@ -52,10 +52,10 @@ asm(".globl PushAllRegistersAndIterateStack             \n"
 
 #else  // !_WIN64
 
-  // We maintain 16-byte alignment at calls. There is an 8-byte return address
-  // on the stack and we push 56 bytes which maintains 16-byte stack alignment
-  // at the call.
-  // Source: https://github.com/hjl-tools/x86-psABI/wiki/x86-64-psABI-1.0.pdf
+// We maintain 16-byte alignment at calls. There is an 8-byte return address
+// on the stack and we push 56 bytes which maintains 16-byte stack alignment
+// at the call.
+// Source: https://github.com/hjl-tools/x86-psABI/wiki/x86-64-psABI-1.0.pdf
 asm(
 #ifdef __APPLE__
     ".globl _PushAllRegistersAndIterateStack            \n"