Make venv change work on Darwin

This patch builds on the previous to make prefix resolution work
correctly inside virtual environments on Darwin. The --inherit-argv0
mechanism is insufficient, as on Darwin, Python uses the
_NSGetExecutablePath() call to work out the actual path to its binary.
Since this resolves to the real unwrapped binary, --inherit-argv0 is
little use.

This patch adds a new variant, --inherit-argv0-path, which resolves the
full path before passing it to argv[0]. On Darwin this is done using
_NSGetExecutablePath(), on Linux by reading /proc/self/exe. This
bypasses the real_executable lookup, as Python gives precedence to
argv[0] when it appears to be a path (contains a slash).

While not strictly necessary on Linux (as --inherit-argv0 works anyway),
the change is made to both for consistency.

3 files changed, 77 insertions, 2 deletions

diff --git a/pkgs/build-support/setup-hooks/make-binary-wrapper/make-binary-wrapper.sh b/pkgs/build-support/setup-hooks/make-binary-wrapper/make-binary-wrapper.sh
index 6cd01f6bf630..cb33fb9cfd84 100644
--- a/pkgs/build-support/setup-hooks/make-binary-wrapper/make-binary-wrapper.sh
+++ b/pkgs/build-support/setup-hooks/make-binary-wrapper/make-binary-wrapper.sh
@@ -19,6 +19,8 @@ assertExecutable() {
 #                          (if unset or empty, defaults to EXECUTABLE)
 # --inherit-argv0        : the executable inherits argv0 from the wrapper.
 #                          (use instead of --argv0 '$0')
+# --inherit-argv0-path   : set the name of the executed process to the full path
+#                          to the wrapper.
 # --set          VAR VAL : add VAR with value VAL to the executable's environment
 # --set-default  VAR VAL : like --set, but only adds VAR if not already set in
 #                          the environment
@@ -87,6 +89,7 @@ makeDocumentedCWrapper() {
 makeCWrapper() {
     local argv0 inherit_argv0 n params cmd main flagsBefore flagsAfter flags executable length
     local uses_prefix uses_suffix uses_assert uses_assert_success uses_stdio uses_asprintf
+    local inherit_argv0_path
     executable=$(escapeStringLiteral "$1")
     params=("$@")
     length=${#params[*]}
@@ -169,6 +172,11 @@ makeCWrapper() {
                 # Whichever comes last of --argv0 and --inherit-argv0 wins
                 inherit_argv0=1
             ;;
+            --inherit-argv0-path)
+                inherit_argv0=1
+                inherit_argv0_path=1
+                uses_stdio=1
+            ;;
             *) # Using an error macro, we will make sure the compiler gives an understandable error message
                 main="$main#error makeCWrapper: Unknown argument ${p}"$'\n'
             ;;
@@ -176,16 +184,19 @@ makeCWrapper() {
     done
     [[ -z "$flagsBefore" && -z "$flagsAfter" ]] || main="$main"${main:+$'\n'}$(addFlags "$flagsBefore" "$flagsAfter")$'\n'$'\n'
     [ -z "$inherit_argv0" ] && main="${main}argv[0] = \"${argv0:-${executable}}\";"$'\n'
+    [[ -n "$inherit_argv0" && -n "$inherit_argv0_path" ]] && main="${main}argv[0] = resolve_path(argv[0]);"$'\n'
     main="${main}return execv(\"${executable}\", argv);"$'\n'
 
-    [ -z "$uses_asprintf" ] || printf '%s\n' "#define _GNU_SOURCE         /* See feature_test_macros(7) */"
+    [[ -z "$uses_asprintf" && -z "$inherit_argv0_path" ]] || printf '%s\n' "#define _GNU_SOURCE         /* See feature_test_macros(7) */"
     printf '%s\n' "#include <unistd.h>"
     printf '%s\n' "#include <stdlib.h>"
     [ -z "$uses_assert" ]   || printf '%s\n' "#include <assert.h>"
     [ -z "$uses_stdio" ]    || printf '%s\n' "#include <stdio.h>"
+    [ -z "$inherit_argv0_path" ] || printf '%s\n' "$(resolvePathInclude)"
     [ -z "$uses_assert_success" ] || printf '\n%s\n' "#define assert_success(e) do { if ((e) < 0) { perror(#e); abort(); } } while (0)"
     [ -z "$uses_prefix" ] || printf '\n%s\n' "$(setEnvPrefixFn)"
     [ -z "$uses_suffix" ] || printf '\n%s\n' "$(setEnvSuffixFn)"
+    [ -z "$inherit_argv0_path" ] || printf '\n%s\n' "$(resolvePathFn)"
     printf '\n%s' "int main(int argc, char **argv) {"
     printf '\n%s' "$(indent4 "$main")"
     printf '\n%s\n' "}"
@@ -338,6 +349,66 @@ void set_env_suffix(char *env, char *sep, char *suffix) {
 "
 }
 
+resolvePathInclude() {
+    printf '%s' "\
+#ifdef __APPLE__
+#include <mach-o/dyld.h>
+#else
+#include <fcntl.h>
+#include <sys/stat.h>
+#endif
+"
+}
+
+resolvePathFn() {
+    printf '%s' "\
+char* resolve_path(char* b) {
+    if (b[0] == '/' || access(b, R_OK | X_OK) == 0)
+        return b;
+
+#ifdef __APPLE__
+    unsigned len = 0;
+    _NSGetExecutablePath(NULL, &len);
+    char* buf = calloc(1, len);
+    if (!buf)
+        return b;
+
+    return _NSGetExecutablePath(buf, &len) == 0 ? buf : b;
+#else
+    int fd = open(\"/proc/self/exe\", O_PATH | O_NOFOLLOW);
+    if (fd < 0) {
+        perror(\"open(/proc/self/exe)\");
+        return b;
+    }
+
+    struct stat st;
+    if (fstat(fd, &st) < 0) {
+        perror(\"fstat(/proc/self/exe)\");
+        close(fd);
+        return b;
+    }
+
+    char* buf = calloc(1, st.st_size + 1);
+    if (!buf) {
+        close(fd);
+        return b;
+    }
+
+    ssize_t res = readlinkat(fd, \"\", buf, st.st_size + 1);
+    if (res != st.st_size) {
+        if (res < 0)
+            perror(\"readlinkat(/proc/self/exe)\");
+        free(buf);
+        close(fd);
+        return b;
+    }
+
+    return buf;
+#endif
+}
+"
+}
+
 # Embed a C string which shows up as readable text in the compiled binary wrapper,
 # giving instructions for recreating the wrapper.
 # Keep in sync with makeBinaryWrapper.extractCmd
diff --git a/pkgs/build-support/setup-hooks/make-wrapper.sh b/pkgs/build-support/setup-hooks/make-wrapper.sh
index 11b332bfc3eb..a44fb6d70547 100644
--- a/pkgs/build-support/setup-hooks/make-wrapper.sh
+++ b/pkgs/build-support/setup-hooks/make-wrapper.sh
@@ -15,6 +15,8 @@ assertExecutable() {
 #                          (if unset or empty, defaults to EXECUTABLE)
 # --inherit-argv0        : the executable inherits argv0 from the wrapper.
 #                          (use instead of --argv0 '$0')
+# --inherit-argv0-path   : set the name of the executed process to the full path
+#                          to the wrapper.
 # --set          VAR VAL : add VAR with value VAL to the executable's environment
 # --set-default  VAR VAL : like --set, but only adds VAR if not already set in
 #                          the environment
@@ -177,6 +179,8 @@ makeShellWrapper() {
         elif [[ "$p" == "--inherit-argv0" ]]; then
             # Whichever comes last of --argv0 and --inherit-argv0 wins
             argv0='$0'
+        elif [[ "$p" == "--inherit-argv0-path" ]]; then
+            argv0='$(which "$0")'
         else
             die "makeWrapper doesn't understand the arg $p"
         fi
diff --git a/pkgs/development/interpreters/python/wrapper.nix b/pkgs/development/interpreters/python/wrapper.nix
index 7c419d320f50..225a2f38b278 100644
--- a/pkgs/development/interpreters/python/wrapper.nix
+++ b/pkgs/development/interpreters/python/wrapper.nix
@@ -49,7 +49,7 @@ let
                   sed -e '1d' -e '3d' ".$prg-wrapped" >> "$out/bin/$prg"
                   chmod +x "$out/bin/$prg"
                 else
-                  makeWrapper "$path/bin/$prg" "$out/bin/$prg" --argv0 "$out/bin/$prg" ${lib.optionalString (!permitUserSite) ''--set PYTHONNOUSERSITE "true"''} ${lib.concatStringsSep " " makeWrapperArgs}
+                  makeWrapper "$path/bin/$prg" "$out/bin/$prg" --inherit-argv0-path ${lib.optionalString (!permitUserSite) ''--set PYTHONNOUSERSITE "true"''} ${lib.concatStringsSep " " makeWrapperArgs}
                 fi
               fi
             fi