gcc: prevent runtime references via __FILE__ but in a reversible manner

the mangling done by mangle-NIX_STORE-in-__FILE__.patch also applies to
source paths embedded in debug symbols. When putting a breakpoint in a
template instanciation from another lib, the path that gdb looks for is
therefore mangled (/nix/store/eeeeeee;...-the-lib-dev/include/foo.h)
This severely degrades the debugging experience. To alleviate that, it's
possible to make the mangling reversible: a debuginfod server can then
reverse the mangling. I plan to implement that in nixseparatedebuginfod.
The reversible mangling that was chosen in making the hash of the store
path uppercase.

pkgs/development/compilers/gcc/patches/12/mangle-NIX_STORE-in-__FILE__.patch

@@ -12,9 +12,20 @@ inputs to be retained in runtime closure.
 Typical examples are `nix` -> `nlohmann_json` and `pipewire` ->
 `lttng-ust.dev`.
 
+For this reason we want to remove the occurrences of hashes in the
+expansion of `__FILE__`. `nuke-references` does it by replacing hashes
+by `eeeeee...` but those paths are also used for debug symbols. It is
+handy to be able to invert the transformation to go back to the original
+store path for debuginfod servers. The chosen solution is to make the
+hash uppercase:
+- it does not trigger runtime references (except for all digit hashes,
+  which are unlikely enough)
+- it visually looks like a bogus store path
+- it is easy to find the original store path if required
+
 Ideally we would like to use `-fmacro-prefix-map=` feature of `gcc` as:
 
-  -fmacro-prefix-map=/nix/store/$hash1-nlohmann-json-ver=/nix/store/eeee.eee-nlohmann-json-ver
+  -fmacro-prefix-map=/nix/store/$hash1-nlohmann-json-ver=/nix/store/$HASH1-nlohmann-json-ver
   -fmacro-prefix-map=/nix/...
 
 In practice it quickly exhausts argument length limit due to `gcc`
@@ -25,9 +36,9 @@ is present in the environment.
 
 Tested as:
 
-    $ printf "# 0 \"/nix/store/01234567890123456789012345678901-pppppp-vvvvvvv\" \nconst char * f(void) { return __FILE__; }" | NIX_STORE=/nix/store ./gcc/xgcc -Bgcc -x c - -S -o -
+    $ printf "# 0 \"/nix/store/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-pppppp-vvvvvvv\" \nconst char * f(void) { return __FILE__; }" | NIX_STORE=/nix/store ./gcc/xgcc -Bgcc -x c - -S -o -
     ...
-    .string "/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-pppppp-vvvvvvv"
+    .string "/nix/store/AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA-pppppp-vvvvvvv"
     ...
 
 Mangled successfully.
@@ -43,7 +54,7 @@ Mangled successfully.
  /* Perform user-specified mapping of filename prefixes.  Return the
     GC-allocated new name corresponding to FILENAME or FILENAME if no
     remapping was performed.  */
-@@ -76,7 +79,30 @@ remap_filename (file_prefix_map *maps, const char *filename)
+@@ -76,7 +79,31 @@ remap_filename (file_prefix_map *maps, const char *filename)
      if (filename_ncmp (filename, map->old_prefix, map->old_len) == 0)
        break;
    if (!map)
@@ -51,8 +62,7 @@ Mangled successfully.
 +    {
 +      if (maps == macro_prefix_maps)
 +	{
-+	  /* Remap all fo $NIX_STORE/.{32} paths to
-+	  * equivalent $NIX_STORE/e{32}.
++	  /* Remap the 32 characters after $NIX_STORE/ to uppercase
 +	  *
 +	  * That way we avoid argument parameters explosion
 +	  * and still avoid embedding headers into runtime closure:
@@ -66,7 +76,9 @@ Mangled successfully.
 +	    {
 +	       s = (char *) ggc_alloc_atomic (name_len + 1);
 +	       memcpy(s, name, name_len + 1);
-+	       memset(s + nix_store_len + 1, 'e', 32);
++	       for (int i = nix_store_len + 1; i < nix_store_len + 1 + 32; i++) {
++		 s[i] = TOUPPER(s[i]);
++	       }
 +	       return s;
 +	    }
 +	}
@@ -75,7 +87,7 @@ Mangled successfully.
    name = filename + map->old_len;
    name_len = strlen (name) + 1;
  
-@@ -90,7 +116,6 @@ remap_filename (file_prefix_map *maps, const char *filename)
+@@ -90,7 +117,6 @@ remap_filename (file_prefix_map *maps, const char *filename)
     ignore it in DW_AT_producer (dwarf2out.cc).  */
  
  /* Linked lists of file_prefix_map structures.  */

pkgs/development/compilers/gcc/patches/13/mangle-NIX_STORE-in-__FILE__.patch

@@ -12,9 +12,20 @@ inputs to be retained in runtime closure.
 Typical examples are `nix` -> `nlohmann_json` and `pipewire` ->
 `lttng-ust.dev`.
 
+For this reason we want to remove the occurrences of hashes in the
+expansion of `__FILE__`. `nuke-references` does it by replacing hashes
+by `eeeeee...` but those paths are also used for debug symbols. It is
+handy to be able to invert the transformation to go back to the original
+store path for debuginfod servers. The chosen solution is to make the
+hash uppercase:
+- it does not trigger runtime references (except for all digit hashes,
+  which are unlikely enough)
+- it visually looks like a bogus store path
+- it is easy to find the original store path if required
+
 Ideally we would like to use `-fmacro-prefix-map=` feature of `gcc` as:
 
-  -fmacro-prefix-map=/nix/store/$hash1-nlohmann-json-ver=/nix/store/eeee.eee-nlohmann-json-ver
+  -fmacro-prefix-map=/nix/store/$hash1-nlohmann-json-ver=/nix/store/$HASH1-nlohmann-json-ver
   -fmacro-prefix-map=/nix/...
 
 In practice it quickly exhausts argument length limit due to `gcc`
@@ -25,9 +36,9 @@ is present in the environment.
 
 Tested as:
 
-    $ printf "# 0 \"/nix/store/01234567890123456789012345678901-pppppp-vvvvvvv\" \nconst char * f(void) { return __FILE__; }" | NIX_STORE=/nix/store ./gcc/xgcc -Bgcc -x c - -S -o -
+    $ printf "# 0 \"/nix/store/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-pppppp-vvvvvvv\" \nconst char * f(void) { return __FILE__; }" | NIX_STORE=/nix/store ./gcc/xgcc -Bgcc -x c - -S -o -
     ...
-    .string "/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-pppppp-vvvvvvv"
+    .string "/nix/store/AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA-pppppp-vvvvvvv"
     ...
 
 Mangled successfully.
@@ -43,14 +54,13 @@ Mangled successfully.
  /* Perform user-specified mapping of filename prefixes.  Return the
     GC-allocated new name corresponding to FILENAME or FILENAME if no
     remapping was performed.  */
-@@ -102,6 +105,29 @@ remap_filename (file_prefix_map *maps, const char *filename)
+@@ -102,6 +105,30 @@ remap_filename (file_prefix_map *maps, const char *filename)
        break;
    if (!map)
      {
 +      if (maps == macro_prefix_maps)
 +	{
-+	  /* Remap all fo $NIX_STORE/.{32} paths to
-+	   * equivalent $NIX_STORE/e{32}.
++	  /* Remap all fo $NIX_STORE/.{32} paths to uppercase
 +	   *
 +	   * That way we avoid argument parameters explosion
 +	   * and still avoid embedding headers into runtime closure:
@@ -64,7 +74,9 @@ Mangled successfully.
 +	     {
 +		s = (char *) ggc_alloc_atomic (name_len + 1);
 +		memcpy(s, name, name_len + 1);
-+		memset(s + nix_store_len + 1, 'e', 32);
++		for (int i = nix_store_len + 1; i < nix_store_len + 1 + 32; i++) {
++		  s[i] = TOUPPER(s[i]);
++		}
 +		if (realname != filename)
 +		  free (const_cast <char *> (realname));
 +		return s;
@@ -73,7 +85,7 @@ Mangled successfully.
        if (realname != filename)
  	free (const_cast <char *> (realname));
        return filename;
-@@ -124,7 +150,6 @@ remap_filename (file_prefix_map *maps, const char *filename)
+@@ -124,7 +151,6 @@ remap_filename (file_prefix_map *maps, const char *filename)
     ignore it in DW_AT_producer (gen_command_line_string in opts.cc).  */
  
  /* Linked lists of file_prefix_map structures.  */
@@ -81,4 +93,3 @@ Mangled successfully.
  static file_prefix_map *debug_prefix_maps; /* -fdebug-prefix-map  */
  static file_prefix_map *profile_prefix_maps; /* -fprofile-prefix-map  */
  
-