100 lines
3.7 KiB
Diff
100 lines
3.7 KiB
Diff
From 30908556fece379ffd7c0da96c774d8bd297e459 Mon Sep 17 00:00:00 2001
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From: Sergei Trofimovich <siarheit@google.com>
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Date: Fri, 22 Sep 2023 22:41:49 +0100
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Subject: [PATCH] gcc/file-prefix-map.cc: always mangle __FILE__ into invalid
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store path
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Without the change `__FILE__` used in static inline functions in headers
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embed paths to header files into executable images. For local headers
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it's not a problem, but for headers in `/nix/store` this causes `-dev`
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inputs to be retained in runtime closure.
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Typical examples are `nix` -> `nlohmann_json` and `pipewire` ->
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`lttng-ust.dev`.
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For this reason we want to remove the occurrences of hashes in the
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expansion of `__FILE__`. `nuke-references` does it by replacing hashes
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by `eeeeee...`. It is handy to be able to invert the transformation to
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go back to the original store path. The chosen solution is to make the
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hash uppercase:
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- it does not trigger runtime references (except for all digit hashes,
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which are unlikely enough)
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- it visually looks like a bogus store path
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- it is easy to find the original store path if required
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Ideally we would like to use `-fmacro-prefix-map=` feature of `gcc` as:
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-fmacro-prefix-map=/nix/store/$hash1-nlohmann-json-ver=/nix/store/$HASH1-nlohmann-json-ver
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-fmacro-prefix-map=/nix/...
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In practice it quickly exhausts argument length limit due to `gcc`
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deficiency: https://gcc.gnu.org/PR111527
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Until it's fixed let's hardcode header mangling if $NIX_STORE variable
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is present in the environment.
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Tested as:
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$ printf "# 0 \"/nix/store/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-pppppp-vvvvvvv\" \nconst char * f(void) { return __FILE__; }" | NIX_STORE=/nix/store ./gcc/xgcc -Bgcc -x c - -S -o -
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...
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.string "/nix/store/AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA-pppppp-vvvvvvv"
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...
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Mangled successfully.
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To reverse the effect of the mangle use new `NIX_GCC_DONT_MANGLE_PREFIX_MAP`
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environment variable. It should not normally be needed.
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--- a/gcc/file-prefix-map.cc
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+++ b/gcc/file-prefix-map.cc
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@@ -65,7 +65,7 @@ add_prefix_map (file_prefix_map *&maps, const char *arg, const char *opt)
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remapping was performed. */
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static const char *
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-remap_filename (file_prefix_map *maps, const char *filename)
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+remap_filename (file_prefix_map *maps, const char *filename, bool mangle_nix_store = false)
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{
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file_prefix_map *map;
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char *s;
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@@ -76,7 +76,31 @@ remap_filename (file_prefix_map *maps, const char *filename)
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if (filename_ncmp (filename, map->old_prefix, map->old_len) == 0)
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break;
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if (!map)
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- return filename;
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+ {
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+ if (mangle_nix_store && getenv("NIX_GCC_DONT_MANGLE_PREFIX_MAP") == NULL)
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+ {
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+ /* Remap the 32 characters after $NIX_STORE/ to uppercase
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+ *
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+ * That way we avoid argument parameters explosion
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+ * and still avoid embedding headers into runtime closure:
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+ * https://gcc.gnu.org/PR111527
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+ */
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+ char * nix_store = getenv("NIX_STORE");
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+ size_t nix_store_len = nix_store ? strlen(nix_store) : 0;
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+ const char * name = filename;
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+ size_t name_len = strlen(name);
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+ if (nix_store && name_len >= nix_store_len + 1 + 32 && memcmp(name, nix_store, nix_store_len) == 0)
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+ {
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+ s = (char *) ggc_alloc_atomic (name_len + 1);
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+ memcpy(s, name, name_len + 1);
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+ for (size_t i = nix_store_len + 1; i < nix_store_len + 1 + 32; i++) {
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+ s[i] = TOUPPER(s[i]);
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+ }
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+ return s;
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+ }
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+ }
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+ return filename;
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+ }
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name = filename + map->old_len;
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name_len = strlen (name) + 1;
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@@ -129,7 +153,7 @@ add_profile_prefix_map (const char *arg)
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const char *
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remap_macro_filename (const char *filename)
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{
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- return remap_filename (macro_prefix_maps, filename);
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+ return remap_filename (macro_prefix_maps, filename, true);
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}
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/* Remap using -fdebug-prefix-map. Return the GC-allocated new name
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