[crt] Stringize __USER_LABEL_PREFIX__ in asm strings

[barannikov88]

Summary

__USER_LABEL_PREFIX__ is not a string (usually it is just _ if not
empty). It must be stringized for string concatenation to work.

[MaskRay]

The code only makes sense for some ELF platforms, not Mach-O platforms where __USER_LABEL_PREFIX__ is (usually) _.
What platforms are you building the code with and seeing a problem?

If we want to make some changes, likely we should just remove __USER_LABEL_PREFIX__.

(I'll take a vacation until 2023-04-10, so I will probably not respond in time.)

[barannikov88]

In D147085#4228710, @MaskRay wrote:

The code only makes sense for some ELF platforms, not Mach-O platforms where __USER_LABEL_PREFIX__ is (usually) _.
What platforms are you building the code with and seeing a problem?

An out-of-tree target with an unusual combination ELF + non-empty __USER_LABEL_PREFIX__.
The prefix has only caused troubles; it will probably go away once I am able to build newlib using clang.

If we want to make some changes, likely we should just remove __USER_LABEL_PREFIX__.

I don't know much about the prefix, but I noticed that the same target may configure it differently depending on the target triple.
If you are sure this is always a no-op, I don't mind removing it. (I would still have to keep an extra _ for my target under #ifdef.)
Note that there is also builtins component using the same functionality, and it also looks like the prefix is always empty. Otherwise the bug would have been spotted earlier -- please see D147077.

[barannikov88]

The prefix has only caused troubles; it will probably go away once I am able to build newlib using clang.

Ah, no, it will have to stay.
Speaking in X86 terms:

eax:
  lea eax, [eax]

causes ambiguity. Same for my target. So the labels are prefixed with _.

[barannikov88]

Wait for D147093 resolution.

[barannikov88]

Abandoned in favor of D147093.

compiler-rt/lib/crt/crtbegin.c

 //===-- crtbegin.c - Start of constructors and destructors ----------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include <stddef.h>
 
+#define STR(S) #S
+#define XSTR(S) STR(S)
+#define SYMBOL_NAME(NAME) XSTR(__USER_LABEL_PREFIX__) #NAME
+
 __attribute__((visibility("hidden"))) void *__dso_handle = &__dso_handle;
 
 #ifdef EH_USE_FRAME_REGISTRY
 __extension__ static void *__EH_FRAME_LIST__[]
     __attribute__((section(".eh_frame"), aligned(sizeof(void *)))) = {};
 
 extern void __register_frame_info(const void *, void *) __attribute__((weak));
 extern void *__deregister_frame_info(const void *) __attribute__((weak));

 #endif
 }
 
 #ifdef CRT_HAS_INITFINI_ARRAY
 __attribute__((section(".init_array"),
                used)) static void (*__init)(void) = __do_init;
 #elif defined(__i386__) || defined(__x86_64__)
 __asm__(".pushsection .init,\"ax\",@progbits\n\t"
-    "call " __USER_LABEL_PREFIX__ "__do_init\n\t"
+        "call " SYMBOL_NAME(__do_init) "\n\t"
         ".popsection");
 #elif defined(__riscv)
 __asm__(".pushsection .init,\"ax\",%progbits\n\t"
-        "call " __USER_LABEL_PREFIX__ "__do_init\n\t"
+        "call " SYMBOL_NAME(__do_init) "\n\t"
         ".popsection");
 #elif defined(__arm__) || defined(__aarch64__)
 __asm__(".pushsection .init,\"ax\",%progbits\n\t"
-    "bl " __USER_LABEL_PREFIX__ "__do_init\n\t"
+        "bl " SYMBOL_NAME(__do_init) "\n\t"
         ".popsection");
 #elif defined(__powerpc__) || defined(__powerpc64__)
 __asm__(".pushsection .init,\"ax\",@progbits\n\t"
-    "bl " __USER_LABEL_PREFIX__ "__do_init\n\t"
+        "bl " SYMBOL_NAME(__do_init) "\n\t"
         "nop\n\t"
         ".popsection");
 #elif defined(__sparc__)
 __asm__(".pushsection .init,\"ax\",@progbits\n\t"
-    "call " __USER_LABEL_PREFIX__ "__do_init\n\t"
+        "call " SYMBOL_NAME(__do_init) "\n\t"
         ".popsection");
 #else
 #error "crtbegin without .init_fini array unimplemented for this architecture"
 #endif // CRT_HAS_INITFINI_ARRAY
 
 #ifndef CRT_HAS_INITFINI_ARRAY
 static fp __DTOR_LIST__[]
     __attribute__((section(".dtors"), aligned(sizeof(fp)))) = {(fp)-1};
 extern fp __DTOR_LIST_END__[];

 #endif
 }
 
 #ifdef CRT_HAS_INITFINI_ARRAY
 __attribute__((section(".fini_array"),
                used)) static void (*__fini)(void) = __do_fini;
 #elif defined(__i386__) || defined(__x86_64__)
 __asm__(".pushsection .fini,\"ax\",@progbits\n\t"
-    "call " __USER_LABEL_PREFIX__ "__do_fini\n\t"
+        "call " SYMBOL_NAME(__do_fini) "\n\t"
         ".popsection");
 #elif defined(__arm__) || defined(__aarch64__)
 __asm__(".pushsection .fini,\"ax\",%progbits\n\t"
-    "bl " __USER_LABEL_PREFIX__ "__do_fini\n\t"
+        "bl " SYMBOL_NAME(__do_fini) "\n\t"
         ".popsection");
 #elif defined(__powerpc__) || defined(__powerpc64__)
 __asm__(".pushsection .fini,\"ax\",@progbits\n\t"
-    "bl " __USER_LABEL_PREFIX__ "__do_fini\n\t"
+        "bl " SYMBOL_NAME(__do_fini) "\n\t"
         "nop\n\t"
         ".popsection");
 #elif defined(__riscv)
 __asm__(".pushsection .fini,\"ax\",@progbits\n\t"
-        "call " __USER_LABEL_PREFIX__ "__do_fini\n\t"
+        "call " SYMBOL_NAME(__do_fini) "\n\t"
         ".popsection");
 #elif defined(__sparc__)
 __asm__(".pushsection .fini,\"ax\",@progbits\n\t"
-    "call " __USER_LABEL_PREFIX__ "__do_fini\n\t"
+        "call " SYMBOL_NAME(__do_fini) "\n\t"
         ".popsection");
 #else
 #error "crtbegin without .init_fini array unimplemented for this architecture"
-#endif  // CRT_HAS_INIT_FINI_ARRAY
+#endif // CRT_HAS_INIT_FINI_ARRAY