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* [committed] libstdc++: Avoid useless dependency on read_symlink from tzdb
@ 2023-09-01 11:16 Jonathan Wakely
  0 siblings, 0 replies; only message in thread
From: Jonathan Wakely @ 2023-09-01 11:16 UTC (permalink / raw)
  To: libstdc++, gcc-patches

Tested x86_64-linux. Pushed to trunk.

-- >8 --

chrono::tzdb::current_zone uses filesystem::read_symlink, which creates
a dependency on the fs_ops.o object in libstdc++.a, which then creates
dependencies on several OS functions if --gc-sections isn't used. For
more details see PR libstdc++/104167 comment 8 and comment 11.

In the cases where that causes linker failures, we probably don't have
readlink anyway, so the filesystem::read_symlink call will always fail.
Repeat the preprocessor conditions for filesystem::read_symlink in the
body of chrono::tzdb::current_zone so that we don't create a
dependency on fs_ops.o for a function that will always fail.


	* src/c++20/ (tzdb::current_zone): Check configure macros
	for POSIX readlink before using filesystem::read_symlink.
 libstdc++-v3/src/c++20/ | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/libstdc++-v3/src/c++20/ b/libstdc++-v3/src/c++20/
index 0fcbf6a4824..d22cea7e070 100644
--- a/libstdc++-v3/src/c++20/
+++ b/libstdc++-v3/src/c++20/
@@ -1635,6 +1635,9 @@ namespace std::chrono
     // TODO cache this function's result?
 #ifndef _AIX
+    // Repeat the preprocessor condition used by filesystem::read_symlink,
+    // to avoid a dependency on src/c++17/fs_ops.o if it won't work anyway.
     error_code ec;
     // This should be a symlink to e.g. /usr/share/zoneinfo/Europe/London
     auto path = filesystem::read_symlink("/etc/localtime", ec);
@@ -1653,6 +1656,7 @@ namespace std::chrono
 	      return tz;
     // Otherwise, look for a file naming the time zone.
     string_view files[] {
       "/etc/timezone",    // Debian derivates

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2023-09-01 11:16 [committed] libstdc++: Avoid useless dependency on read_symlink from tzdb Jonathan Wakely

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