Remove guesswork from getStackPointerGlobal. NFC

sbc100 · sbc100 · commit 8e2c2be93749 · 2026-05-06T17:11:05.000-07:00
We were just assuming that if no `__stack_pointer` was imported then the first global must be the `__stack_pointer`. Instead we can just require that the global be names correctly in the name section. This will require an emscripten-side change to ensure names are generated when running this pass. Needed for fixing emscripten-core/emscripten#24964.
diff --git a/src/wasm/wasm-emscripten.cpp b/src/wasm/wasm-emscripten.cpp
@@ -40,17 +40,10 @@ void addExportedFunction(Module& wasm, Function* function) {
 }
 
 Global* getStackPointerGlobal(Module& wasm) {
-  // Assumption: The stack pointer is either imported as __stack_pointer or
-  // we just assume it's the first non-imported global.
-  // TODO(sbc): Find a better way to discover the stack pointer.  Perhaps the
-  // linker could export it by name?
+  // Assumption: The stack pointer is either be and imported global called
+  // __stack_pointer or a defined global with that name.
   for (auto& g : wasm.globals) {
-    if (g->imported() && g->base == STACK_POINTER) {
-      return g.get();
-    }
-  }
-  for (auto& g : wasm.globals) {
-    if (!g->imported()) {
+    if (g->base == STACK_POINTER || g->name == STACK_POINTER) {
       return g.get();
     }
   }
diff --git a/test/finalize/recursive_safe_stack.wat b/test/finalize/recursive_safe_stack.wat
@@ -6,7 +6,7 @@
  (memory $0 2)
  (data (i32.const 568) "%d:%d\n\00Result: %d\n\00")
  (table $0 1 1 funcref)
- (global $global$0 (mut i32) (i32.const 66128))
+ (global $__stack_pointer (mut i32) (i32.const 66128))
  (global $global$1 i32 (i32.const 66128))
  (global $global$2 i32 (i32.const 587))
  (export "memory" (memory $0))
@@ -18,10 +18,10 @@
  )
  (func $foo (; 2 ;) (type $0) (param $0 i32) (param $1 i32) (result i32)
   (local $2 i32)
-  (global.set $global$0
+  (global.set $__stack_pointer
    (local.tee $2
     (i32.sub
-     (global.get $global$0)
+     (global.get $__stack_pointer)
      (i32.const 16)
     )
    )
@@ -40,7 +40,7 @@
     (local.get $2)
    )
   )
-  (global.set $global$0
+  (global.set $__stack_pointer
    (i32.add
     (local.get $2)
     (i32.const 16)
@@ -53,10 +53,10 @@
  )
  (func $__original_main (; 3 ;) (type $2) (result i32)
   (local $0 i32)
-  (global.set $global$0
+  (global.set $__stack_pointer
    (local.tee $0
     (i32.sub
-     (global.get $global$0)
+     (global.get $__stack_pointer)
      (i32.const 16)
     )
    )
@@ -74,7 +74,7 @@
     (local.get $0)
    )
   )
-  (global.set $global$0
+  (global.set $__stack_pointer
    (i32.add
     (local.get $0)
     (i32.const 16)
diff --git a/test/finalize/recursive_safe_stack.wat.out b/test/finalize/recursive_safe_stack.wat.out
@@ -6,7 +6,7 @@
  (type $4 (func (param i32 i32)))
  (import "env" "printf" (func $printf (param i32 i32) (result i32)))
  (import "env" "__handle_stack_overflow" (func $__handle_stack_overflow (param i32)))
- (global $global$0 (mut i32) (i32.const 66128))
+ (global $__stack_pointer (mut i32) (i32.const 66128))
  (global $global$1 i32 (i32.const 66128))
  (global $global$2 i32 (i32.const 587))
  (global $__stack_base (mut i32) (i32.const 0))
@@ -33,7 +33,7 @@
       (local.tee $3
        (local.tee $2
         (i32.sub
-         (global.get $global$0)
+         (global.get $__stack_pointer)
          (i32.const 16)
         )
        )
@@ -51,7 +51,7 @@
      )
     )
    )
-   (global.set $global$0
+   (global.set $__stack_pointer
     (local.get $3)
    )
   )
@@ -92,7 +92,7 @@
      )
     )
    )
-   (global.set $global$0
+   (global.set $__stack_pointer
     (local.get $4)
    )
   )
@@ -112,7 +112,7 @@
       (local.tee $1
        (local.tee $0
         (i32.sub
-         (global.get $global$0)
+         (global.get $__stack_pointer)
          (i32.const 16)
         )
        )
@@ -130,7 +130,7 @@
      )
     )
    )
-   (global.set $global$0
+   (global.set $__stack_pointer
     (local.get $1)
    )
   )
@@ -170,7 +170,7 @@
      )
     )
    )
-   (global.set $global$0
+   (global.set $__stack_pointer
     (local.get $2)
    )
   )
diff --git a/test/finalize/safe_stack_standalone-wasm.wat b/test/finalize/safe_stack_standalone-wasm.wat
@@ -6,7 +6,7 @@
  (memory $0 2)
  (data (i32.const 568) "%d:%d\n\00Result: %d\n\00")
  (table $0 1 1 funcref)
- (global $global$0 (mut i32) (i32.const 66128))
+ (global $__stack_pointer (mut i32) (i32.const 66128))
  (global $global$1 i32 (i32.const 66128))
  (global $global$2 i32 (i32.const 587))
  (export "memory" (memory $0))
@@ -18,10 +18,10 @@
  )
  (func $foo (; 2 ;) (type $0) (param $0 i32) (param $1 i32) (result i32)
   (local $2 i32)
-  (global.set $global$0
+  (global.set $__stack_pointer
    (local.tee $2
     (i32.sub
-     (global.get $global$0)
+     (global.get $__stack_pointer)
      (i32.const 16)
     )
    )
@@ -40,7 +40,7 @@
     (local.get $2)
    )
   )
-  (global.set $global$0
+  (global.set $__stack_pointer
    (i32.add
     (local.get $2)
     (i32.const 16)
@@ -53,10 +53,10 @@
  )
  (func $__original_main (; 3 ;) (type $2) (result i32)
   (local $0 i32)
-  (global.set $global$0
+  (global.set $__stack_pointer
    (local.tee $0
     (i32.sub
-     (global.get $global$0)
+     (global.get $__stack_pointer)
      (i32.const 16)
     )
    )
@@ -74,7 +74,7 @@
     (local.get $0)
    )
   )
-  (global.set $global$0
+  (global.set $__stack_pointer
    (i32.add
     (local.get $0)
     (i32.const 16)
diff --git a/test/finalize/safe_stack_standalone-wasm.wat.out b/test/finalize/safe_stack_standalone-wasm.wat.out
@@ -4,7 +4,7 @@
  (type $2 (func (result i32)))
  (type $3 (func (param i32 i32)))
  (import "env" "printf" (func $printf (param i32 i32) (result i32)))
- (global $global$0 (mut i32) (i32.const 66128))
+ (global $__stack_pointer (mut i32) (i32.const 66128))
  (global $global$1 i32 (i32.const 66128))
  (global $global$2 i32 (i32.const 587))
  (global $__stack_base (mut i32) (i32.const 0))
@@ -31,7 +31,7 @@
       (local.tee $3
        (local.tee $2
         (i32.sub
-         (global.get $global$0)
+         (global.get $__stack_pointer)
          (i32.const 16)
         )
        )
@@ -47,7 +47,7 @@
      (unreachable)
     )
    )
-   (global.set $global$0
+   (global.set $__stack_pointer
     (local.get $3)
    )
   )
@@ -86,7 +86,7 @@
      (unreachable)
     )
    )
-   (global.set $global$0
+   (global.set $__stack_pointer
     (local.get $4)
    )
   )
@@ -106,7 +106,7 @@
       (local.tee $1
        (local.tee $0
         (i32.sub
-         (global.get $global$0)
+         (global.get $__stack_pointer)
          (i32.const 16)
         )
        )
@@ -122,7 +122,7 @@
      (unreachable)
     )
    )
-   (global.set $global$0
+   (global.set $__stack_pointer
     (local.get $1)
    )
   )
@@ -160,7 +160,7 @@
      (unreachable)
     )
    )
-   (global.set $global$0
+   (global.set $__stack_pointer
     (local.get $2)
    )
   )
diff --git a/test/passes/spill-pointers.txt b/test/passes/spill-pointers.txt
diff --git a/test/passes/spill-pointers.wast b/test/passes/spill-pointers.wast

Original file line number	Diff line number	Diff line change
`@@ -6,7 +6,7 @@`
`6`	`6`	`(memory $0 2)`
`7`	`7`	`(data (i32.const 568) "%d:%d\n\00Result: %d\n\00")`
`8`	`8`	`(table $0 1 1 funcref)`
`9`		`- (global $global$0 (mut i32) (i32.const 66128))`
	`9`	`+ (global $__stack_pointer (mut i32) (i32.const 66128))`
`10`	`10`	`(global $global$1 i32 (i32.const 66128))`
`11`	`11`	`(global $global$2 i32 (i32.const 587))`
`12`	`12`	`(export "memory" (memory $0))`
`@@ -18,10 +18,10 @@`
`18`	`18`	`)`
`19`	`19`	`(func $foo (; 2 ;) (type $0) (param $0 i32) (param $1 i32) (result i32)`
`20`	`20`	`(local $2 i32)`
`21`		`- (global.set $global$0`
	`21`	`+ (global.set $__stack_pointer`
`22`	`22`	`(local.tee $2`
`23`	`23`	`(i32.sub`
`24`		`- (global.get $global$0)`
	`24`	`+ (global.get $__stack_pointer)`
`25`	`25`	`(i32.const 16)`
`26`	`26`	`)`
`27`	`27`	`)`
`@@ -40,7 +40,7 @@`
`40`	`40`	`(local.get $2)`
`41`	`41`	`)`
`42`	`42`	`)`
`43`		`- (global.set $global$0`
	`43`	`+ (global.set $__stack_pointer`
`44`	`44`	`(i32.add`
`45`	`45`	`(local.get $2)`
`46`	`46`	`(i32.const 16)`
`@@ -53,10 +53,10 @@`
`53`	`53`	`)`
`54`	`54`	`(func $__original_main (; 3 ;) (type $2) (result i32)`
`55`	`55`	`(local $0 i32)`
`56`		`- (global.set $global$0`
	`56`	`+ (global.set $__stack_pointer`
`57`	`57`	`(local.tee $0`
`58`	`58`	`(i32.sub`
`59`		`- (global.get $global$0)`
	`59`	`+ (global.get $__stack_pointer)`
`60`	`60`	`(i32.const 16)`
`61`	`61`	`)`
`62`	`62`	`)`
`@@ -74,7 +74,7 @@`
`74`	`74`	`(local.get $0)`
`75`	`75`	`)`
`76`	`76`	`)`
`77`		`- (global.set $global$0`
	`77`	`+ (global.set $__stack_pointer`
`78`	`78`	`(i32.add`
`79`	`79`	`(local.get $0)`
`80`	`80`	`(i32.const 16)`
Original file line number	Diff line number	Diff line change
`@@ -6,7 +6,7 @@`
`6`	`6`	`(type $4 (func (param i32 i32)))`
`7`	`7`	`(import "env" "printf" (func $printf (param i32 i32) (result i32)))`
`8`	`8`	`(import "env" "__handle_stack_overflow" (func $__handle_stack_overflow (param i32)))`
`9`		`- (global $global$0 (mut i32) (i32.const 66128))`
	`9`	`+ (global $__stack_pointer (mut i32) (i32.const 66128))`
`10`	`10`	`(global $global$1 i32 (i32.const 66128))`
`11`	`11`	`(global $global$2 i32 (i32.const 587))`
`12`	`12`	`(global $__stack_base (mut i32) (i32.const 0))`
`@@ -33,7 +33,7 @@`
`33`	`33`	`(local.tee $3`
`34`	`34`	`(local.tee $2`
`35`	`35`	`(i32.sub`
`36`		`- (global.get $global$0)`
	`36`	`+ (global.get $__stack_pointer)`
`37`	`37`	`(i32.const 16)`
`38`	`38`	`)`
`39`	`39`	`)`
`@@ -51,7 +51,7 @@`
`51`	`51`	`)`
`52`	`52`	`)`
`53`	`53`	`)`
`54`		`- (global.set $global$0`
	`54`	`+ (global.set $__stack_pointer`
`55`	`55`	`(local.get $3)`
`56`	`56`	`)`
`57`	`57`	`)`
`@@ -92,7 +92,7 @@`
`92`	`92`	`)`
`93`	`93`	`)`
`94`	`94`	`)`
`95`		`- (global.set $global$0`
	`95`	`+ (global.set $__stack_pointer`
`96`	`96`	`(local.get $4)`
`97`	`97`	`)`
`98`	`98`	`)`
`@@ -112,7 +112,7 @@`
`112`	`112`	`(local.tee $1`
`113`	`113`	`(local.tee $0`
`114`	`114`	`(i32.sub`
`115`		`- (global.get $global$0)`
	`115`	`+ (global.get $__stack_pointer)`
`116`	`116`	`(i32.const 16)`
`117`	`117`	`)`
`118`	`118`	`)`
`@@ -130,7 +130,7 @@`
`130`	`130`	`)`
`131`	`131`	`)`
`132`	`132`	`)`
`133`		`- (global.set $global$0`
	`133`	`+ (global.set $__stack_pointer`
`134`	`134`	`(local.get $1)`
`135`	`135`	`)`
`136`	`136`	`)`
`@@ -170,7 +170,7 @@`
`170`	`170`	`)`
`171`	`171`	`)`
`172`	`172`	`)`
`173`		`- (global.set $global$0`
	`173`	`+ (global.set $__stack_pointer`
`174`	`174`	`(local.get $2)`
`175`	`175`	`)`
`176`	`176`	`)`
Original file line number	Diff line number	Diff line change
`@@ -4,7 +4,7 @@`
`4`	`4`	`(type $2 (func (result i32)))`
`5`	`5`	`(type $3 (func (param i32 i32)))`
`6`	`6`	`(import "env" "printf" (func $printf (param i32 i32) (result i32)))`
`7`		`- (global $global$0 (mut i32) (i32.const 66128))`
	`7`	`+ (global $__stack_pointer (mut i32) (i32.const 66128))`
`8`	`8`	`(global $global$1 i32 (i32.const 66128))`
`9`	`9`	`(global $global$2 i32 (i32.const 587))`
`10`	`10`	`(global $__stack_base (mut i32) (i32.const 0))`
`@@ -31,7 +31,7 @@`
`31`	`31`	`(local.tee $3`
`32`	`32`	`(local.tee $2`
`33`	`33`	`(i32.sub`
`34`		`- (global.get $global$0)`
	`34`	`+ (global.get $__stack_pointer)`
`35`	`35`	`(i32.const 16)`
`36`	`36`	`)`
`37`	`37`	`)`
`@@ -47,7 +47,7 @@`
`47`	`47`	`(unreachable)`
`48`	`48`	`)`
`49`	`49`	`)`
`50`		`- (global.set $global$0`
	`50`	`+ (global.set $__stack_pointer`
`51`	`51`	`(local.get $3)`
`52`	`52`	`)`
`53`	`53`	`)`
`@@ -86,7 +86,7 @@`
`86`	`86`	`(unreachable)`
`87`	`87`	`)`
`88`	`88`	`)`
`89`		`- (global.set $global$0`
	`89`	`+ (global.set $__stack_pointer`
`90`	`90`	`(local.get $4)`
`91`	`91`	`)`
`92`	`92`	`)`
`@@ -106,7 +106,7 @@`
`106`	`106`	`(local.tee $1`
`107`	`107`	`(local.tee $0`
`108`	`108`	`(i32.sub`
`109`		`- (global.get $global$0)`
	`109`	`+ (global.get $__stack_pointer)`
`110`	`110`	`(i32.const 16)`
`111`	`111`	`)`
`112`	`112`	`)`
`@@ -122,7 +122,7 @@`
`122`	`122`	`(unreachable)`
`123`	`123`	`)`
`124`	`124`	`)`
`125`		`- (global.set $global$0`
	`125`	`+ (global.set $__stack_pointer`
`126`	`126`	`(local.get $1)`
`127`	`127`	`)`
`128`	`128`	`)`
`@@ -160,7 +160,7 @@`
`160`	`160`	`(unreachable)`
`161`	`161`	`)`
`162`	`162`	`)`
`163`		`- (global.set $global$0`
	`163`	`+ (global.set $__stack_pointer`
`164`	`164`	`(local.get $2)`
`165`	`165`	`)`
`166`	`166`	`)`