take -pie out of macos hardening build flags

1 files changed, 11 insertions, 8 deletions

diff --git a/DESIGN b/DESIGN
index b25b37c..39d0107 100644
--- a/DESIGN
+++ b/DESIGN
@@ -115,20 +115,23 @@ which costs it part of its last day and nothing else.
 Build hardening the shipped binary
 ----------------------------------
 
-The production and debug binaries carry -fstack-protector-strong, PIE and
-_FORTIFY_SOURCE=2; every linker but Apple's also gets full RELRO (-z relro,-z now). Measured cost on
+The production and debug binaries carry -fstack-protector-strong, -fPIE and
+_FORTIFY_SOURCE=2 on every platform; the GNU-style linkers also get -pie and
+full RELRO (-z relro,-z now). Measured cost on
 the announce hot path is 300 to 305 nanoseconds, under two per cent, and the
 individual flags sit inside the run-to-run noise: add_peer has few stack
 buffers, most buffer sizes are known at compile time so FORTIFY emits no
 runtime check, and PIE on arm64 is almost free. On x86-64 PIE costs a little
 more. End to end it is invisible, since a UDP announce is mostly kernel time.
 
-RELRO is gated on the operating system because Apple's linker rejects -z. The
-branch runs in the shell through a != assignment, the one form both bmake and
-GNU make 4 accept; $(shell) is GNU only and GNU make 3.81, which stock macOS
-ships, has neither. On that old make the != line is inert and leaves RELRO
-empty, which is the right answer for macOS anyway, so every platform resolves
-correctly without a make conditional.
+The link flags -pie and RELRO are gated on the operating system: Apple's
+linker rejects -z, and flags a bare -pie in the combined compile-and-link as
+unused, while macOS links executables PIE by default, so leaving both off
+there costs no hardening. The branch runs in the shell through a != assignment,
+the one form both bmake and GNU make 4 accept; $(shell) is GNU only and GNU
+make 3.81, which stock macOS ships, has neither. On that old make the != line
+is inert and leaves the flags empty, which is the right answer for macOS
+anyway, so every platform resolves correctly without a make conditional.
 
 The flags are not in OT_CFLAGS, so the sanitizer test builds do not inherit
 them. AddressSanitizer checks harder than FORTIFY does, and the two clash on