Mark all labels inside JIT_PatchedCode region as .alt_entry on Apple platforms

Author: filipnavara

src/coreclr/pal/inc/unixasmmacrosamd64.inc

@@ -52,6 +52,25 @@ C_FUNC(\Name):
         .cfi_endproc
 .endm
 
+// Special version of the LEAF_ENTRY macro that should be used inside
+// patchable code region to prevent the linker from relocating the code.
+// On most Unix platforms this is identical to LEAF_ENTRY. However, on
+// Apple platforms it produces the function entry points at .alt_entry
+// symbols that create external labels but keep the whole patched region
+// as single atom for the linker.
+.macro LEAF_ENTRY_PATCHABLE Name, Section
+#if defined(__APPLE__)
+        .text
+        .p2align 4
+        .alt_entry C_FUNC(\Name)
+        .private_extern C_FUNC(\Name)
+C_FUNC(\Name):
+        .cfi_startproc
+#else
+        LEAF_ENTRY \Name, \Section
+#endif
+.endm
+
 .macro LEAF_END_MARKED Name, Section
 #if defined(__APPLE__)
         .alt_entry C_FUNC(\Name\()_End)

src/coreclr/pal/inc/unixasmmacrosarm64.inc

@@ -63,6 +63,25 @@ C_FUNC(\Name):
         .cfi_endproc
 .endm
 
+// Special version of the LEAF_ENTRY macro that should be used inside
+// patchable code region to prevent the linker from relocating the code.
+// On most Unix platforms this is identical to LEAF_ENTRY. However, on
+// Apple platforms it produces the function entry points at .alt_entry
+// symbols that create external labels but keep the whole patched region
+// as single atom for the linker.
+.macro LEAF_ENTRY_PATCHABLE Name, Section
+#if defined(__APPLE__)
+        .text
+        .p2align        2
+        .alt_entry C_FUNC(\Name)
+        .private_extern C_FUNC(\Name)
+C_FUNC(\Name):
+        .cfi_startproc
+#else
+        LEAF_ENTRY \Name, \Section
+#endif
+.endm
+
 .macro LEAF_END_MARKED Name, Section
 #if defined(__APPLE__)
         .alt_entry C_FUNC(\Name\()_End)

src/coreclr/vm/amd64/patchedcode.S

@@ -24,7 +24,7 @@ LEAF_END JIT_PatchedCodeStart, _TEXT
 // it needs to have it's card updated
 //
 // void JIT_CheckedWriteBarrier(Object** dst, Object* src)
-LEAF_ENTRY JIT_CheckedWriteBarrier, _TEXT
+LEAF_ENTRY_PATCHABLE JIT_CheckedWriteBarrier, _TEXT
 
         // When WRITE_BARRIER_CHECK is defined _NotInHeap will write the reference
         // but if it isn't then it will just return.
@@ -54,7 +54,7 @@ LEAF_END_MARKED JIT_CheckedWriteBarrier, _TEXT
 // larger of the two functions (JIT_WriteBarrier_PostGrow) to ensure we have created
 // enough space to copy that code in.
 .balign 16
-LEAF_ENTRY JIT_WriteBarrier, _TEXT
+LEAF_ENTRY_PATCHABLE JIT_WriteBarrier, _TEXT
 #ifdef _DEBUG
         // In debug builds, this just contains jump to the debug version of the write barrier by default
         jmp C_FUNC(JIT_WriteBarrier_Debug)
@@ -240,6 +240,6 @@ LEAF_ENTRY JIT_WriteBarrier, _TEXT
 LEAF_END_MARKED JIT_WriteBarrier, _TEXT
 
 // Mark start of the code region that we patch at runtime
-LEAF_ENTRY JIT_PatchedCodeLast, _TEXT
+LEAF_ENTRY_PATCHABLE JIT_PatchedCodeLast, _TEXT
         ret
 LEAF_END JIT_PatchedCodeLast, _TEXT

src/coreclr/vm/arm64/patchedcode.S

@@ -13,7 +13,7 @@
 // to declare a write barrier function.
 //
 .macro WRITE_BARRIER_ENTRY name
-    LEAF_ENTRY \name, _TEXT
+    LEAF_ENTRY_PATCHABLE \name, _TEXT
 .endm
 
 // WRITE_BARRIER_END
@@ -145,7 +145,7 @@ WRITE_BARRIER_END JIT_WriteBarrier_Table
 
 // ------------------------------------------------------------------
 // End of the writeable code region
-LEAF_ENTRY JIT_PatchedCodeLast, _TEXT
+LEAF_ENTRY_PATCHABLE JIT_PatchedCodeLast, _TEXT
     ret  lr
 LEAF_END JIT_PatchedCodeLast, _TEXT