From b9410061e2ad6fe91bb3910c3adc7d4a315b7ce9 Mon Sep 17 00:00:00 2001
From: Rich Felker <dalias@aerifal.cx>
Date: Mon, 16 Apr 2018 20:12:12 -0400
Subject: use explicit dynamic-list rather than symbolic-functions for linking

we have always bound symbols at libc.so link time rather than runtime
to minimize startup-time relocations and overhead of calls through the
PLT, and possibly also to preclude interposition that would not work
correctly anyway if allowed. historically, binding at link-time was
also necessary for the dynamic linker to work, but the dynamic linker
bootstrap overhaul in commit f3ddd173806fd5c60b3f034528ca24542aecc5b9
made it unnecessary.

our use of -Bsymbolic-functions, rather than -Bsymbolic, was chosen
because the latter is incompatible with public global data; it makes
it incompatible with copy relocations in the main program. however,
not all global data needs to be public. by using --dynamic-list
instead with an explicit list, we can reduce the number of symbolic
relocations left for runtime.

this change will also allow us to permit interposition of specific
functions (e.g. the allocator) if/when we want to, by adding them to
the dynamic list.
---
 dynamic.list | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)
 create mode 100644 dynamic.list

(limited to 'dynamic.list')

diff --git a/dynamic.list b/dynamic.list
new file mode 100644
index 00000000..8b4f2366
--- /dev/null
+++ b/dynamic.list
@@ -0,0 +1,35 @@
+{
+environ;
+__environ;
+
+stdin;
+stdout;
+stderr;
+
+timezone;
+daylight;
+tzname;
+__timezone;
+__daylight;
+__tzname;
+
+signgam;
+__signgam;
+
+optarg;
+optind;
+opterr;
+optreset;
+__optreset;
+
+getdate_err;
+
+h_errno;
+
+program_invocation_name;
+program_invocation_short_name;
+__progname;
+__progname_full;
+
+__stack_chk_guard;
+};
-- 
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