pyrox.dev
1From e160a8cd4a704f4b7724df02b62394f677cc4198 Mon Sep 17 00:00:00 2001
2From: Sergei Trofimovich <siarheit@google.com>
3Date: Fri, 22 Sep 2023 22:41:49 +0100
4Subject: [PATCH] gcc/file-prefix-map.cc: always mangle __FILE__ into invalid
5 store path
6
7Without the change `__FILE__` used in static inline functions in headers
8embed paths to header files into executable images. For local headers
9it's not a problem, but for headers in `/nix/store` this causes `-dev`
10inputs to be retained in runtime closure.
11
12Typical examples are `nix` -> `nlohmann_json` and `pipewire` ->
13`lttng-ust.dev`.
14
15For this reason we want to remove the occurrences of hashes in the
16expansion of `__FILE__`. `nuke-references` does it by replacing hashes
17by `eeeeee...`. It is handy to be able to invert the transformation to
18go back to the original store path. The chosen solution is to make the
19hash uppercase:
20- it does not trigger runtime references (except for all digit hashes,
21 which are unlikely enough)
22- it visually looks like a bogus store path
23- it is easy to find the original store path if required
24
25Ideally we would like to use `-fmacro-prefix-map=` feature of `gcc` as:
26
27 -fmacro-prefix-map=/nix/store/$hash1-nlohmann-json-ver=/nix/store/$HASH1-nlohmann-json-ver
28 -fmacro-prefix-map=/nix/...
29
30In practice it quickly exhausts argument length limit due to `gcc`
31deficiency: https://gcc.gnu.org/PR111527
32
33Until it's fixed let's hardcode header mangling if $NIX_STORE variable
34is present in the environment.
35
36Tested as:
37
38 $ printf "# 0 \"/nix/store/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-pppppp-vvvvvvv\" \nconst char * f(void) { return __FILE__; }" | NIX_STORE=/nix/store ./gcc/xgcc -Bgcc -x c - -S -o -
39 ...
40 .string "/nix/store/AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA-pppppp-vvvvvvv"
41 ...
42
43Mangled successfully.
44
45To reverse the effect of the mangle use new `NIX_GCC_DONT_MANGLE_PREFIX_MAP`
46environment variable. It should not normally be needed.
47--- a/gcc/file-prefix-map.cc
48+++ b/gcc/file-prefix-map.cc
49@@ -74,7 +74,7 @@ add_prefix_map (file_prefix_map *&maps, const char *arg, const char *opt)
50 remapping was performed. */
51
52 static const char *
53-remap_filename (file_prefix_map *maps, const char *filename)
54+remap_filename (file_prefix_map *maps, const char *filename, bool mangle_nix_store = false)
55 {
56 file_prefix_map *map;
57 char *s;
58@@ -102,6 +102,30 @@ remap_filename (file_prefix_map *maps, const char *filename)
59 break;
60 if (!map)
61 {
62+ if (mangle_nix_store && getenv("NIX_GCC_DONT_MANGLE_PREFIX_MAP") == NULL)
63+ {
64+ /* Remap all fo $NIX_STORE/.{32} paths to uppercase
65+ *
66+ * That way we avoid argument parameters explosion
67+ * and still avoid embedding headers into runtime closure:
68+ * https://gcc.gnu.org/PR111527
69+ */
70+ char * nix_store = getenv("NIX_STORE");
71+ size_t nix_store_len = nix_store ? strlen(nix_store) : 0;
72+ const char * name = realname ? realname : filename;
73+ size_t name_len = strlen(name);
74+ if (nix_store && name_len >= nix_store_len + 1 + 32 && memcmp(name, nix_store, nix_store_len) == 0)
75+ {
76+ s = (char *) ggc_alloc_atomic (name_len + 1);
77+ memcpy(s, name, name_len + 1);
78+ for (size_t i = nix_store_len + 1; i < nix_store_len + 1 + 32; i++) {
79+ s[i] = TOUPPER(s[i]);
80+ }
81+ if (realname != filename)
82+ free (const_cast <char *> (realname));
83+ return s;
84+ }
85+ }
86 if (realname != filename)
87 free (const_cast <char *> (realname));
88 return filename;
89@@ -163,7 +187,7 @@ add_profile_prefix_map (const char *arg)
90 const char *
91 remap_macro_filename (const char *filename)
92 {
93- return remap_filename (macro_prefix_maps, filename);
94+ return remap_filename (macro_prefix_maps, filename, true);
95 }
96
97 /* Remap using -fdebug-prefix-map. Return the GC-allocated new name