[PATCH] amdgcn: Use __builtin_gcn_ in libc/machine/amdgcn/getreent.c

[PATCH] amdgcn: Use __builtin_gcn_ in libc/machine/amdgcn/getreent.c

[Tobias Burnus]

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This patch replaces some more hard-coded register use and
coded internal implementation choices by compiler builtins –
added in this case of GCC 13 (mainline). #if conditions are
used to use the builtins if (and only if) they are available
in the used compiler.

Thanks,

Tobias
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From 611559a7939c29afeda6bb585fb6ba846e5a8b0e Mon Sep 17 00:00:00 2001
From: Tobias Burnus <tobias@codesourcery.com>
Date: Tue, 22 Nov 2022 14:53:48 +0100
Subject: [PATCH] amdgcn: Use __builtin_gcn_ in libc/machine/amdgcn/getreent.c

Call __builtin_gcn_get_stack_limit and __builtin_gcn_first_call_this_thread_p
to reduce dependency on some register/layout assumptions by using the new
GCC mainline (GCC 13) builtins, if they are available. If not, the existing
code is used.
---
 newlib/libc/machine/amdgcn/getreent.c | 38 ++++++++++++++++++++-------
 1 file changed, 29 insertions(+), 9 deletions(-)

diff --git a/newlib/libc/machine/amdgcn/getreent.c b/newlib/libc/machine/amdgcn/getreent.c
index be7d2edc9..ef731f649 100644
--- a/newlib/libc/machine/amdgcn/getreent.c
+++ b/newlib/libc/machine/amdgcn/getreent.c
@@ -29,22 +29,42 @@ typedef struct hsa_kernel_dispatch_packet_s {
 struct _reent *
 __getreent (void)
 {
-  /* Place the reent data at the top of the stack allocation.
-     s[0:1] contains a 48-bit private segment base address.
+  /* Place the reent data at the top of the stack allocation.  */
+  struct data {
+    int marker;
+    struct _reent reent;
+  } *data;
+
+#if defined(__has_builtin) \
+    && __has_builtin(__builtin_gcn_get_stack_limit) \
+    && __has_builtin(__builtin_gcn_first_call_this_thread_p)
+  unsigned long addr = (((unsigned long) __builtin_gcn_get_stack_limit()
+			 - sizeof(struct data)) & ~7);
+  data = (struct data *)addr;
+
+  register long sp asm("s16");
+
+  if (sp >= addr)
+    goto stackoverflow;
+  if (__builtin_gcn_first_call_this_thread_p())
+    {
+      data->marker = 12345;
+      __builtin_memset (&data->reent, 0, sizeof(struct _reent));
+      _REENT_INIT_PTR_ZEROED (&data->reent);
+    }
+  else if (data->marker != 12345)
+    goto stackoverflow;
+#else
+  /* s[0:1] contains a 48-bit private segment base address.
      s11 contains the offset to the base of the stack.
      s[4:5] contains the dispatch pointer.
-     
+
      WARNING: this code will break if s[0:1] is ever used for anything!  */
   const register unsigned long buffer_descriptor asm("s0");
   unsigned long private_segment = buffer_descriptor & 0x0000ffffffffffff;
   const register unsigned int stack_offset asm("s11");
   const register hsa_kernel_dispatch_packet_t *dispatch_ptr asm("s4");
 
-  struct data {
-    int marker;
-    struct _reent reent;
-  } *data;
-
   unsigned long stack_base = private_segment + stack_offset;
   unsigned long stack_end = stack_base + dispatch_ptr->private_segment_size * 64;
   unsigned long addr = (stack_end - sizeof(struct data)) & ~7;
@@ -69,7 +89,7 @@ __getreent (void)
     }
   else if (data->marker != 12345)
     goto stackoverflow;
-
+#endif
 
   return &data->reent;
 
-- 
2.25.1