|author||Rich Felker <email@example.com>||2015-11-04 13:24:11 -0500|
|committer||Rich Felker <firstname.lastname@example.org>||2015-11-04 13:24:11 -0500|
have configure check/add -ffunction-sections and -fdata-sections
based on patch by Denys Vlasenko. the original intent for using these options was to enable linking optimizations. these are immediately available for static linking applications to libc.a, and will also be used for linking libc.so in a subsequent commit. in addition to the original motives, this change works around a whole class of toolchain bugs where the compiler generates relative address expressions using a weak symbol and the assembler "optimizes out" the relocation which should result by using the weak definition. (see gas pr 18561 and gcc pr 66609, 68178, etc. for examples.) by having different functions and data objects in their own sections, all relative address expressions are cross-section and thus cannot be resolved to constants until link time. this allows us to retain support for affected compiler/assembler versions without invasive and fragile source-level workarounds.
1 files changed, 11 insertions, 0 deletions
@@ -437,6 +437,17 @@ tryflag CFLAGS_AUTO -fno-unwind-tables
tryflag CFLAGS_AUTO -fno-asynchronous-unwind-tables
+# Attempt to put each function and each data object in its own
+# section. This both allows additional size optimizations at link
+# time and works around a dangerous class of compiler/assembler bugs
+# whereby relative address expressions are constant-folded by the
+# assembler even when one or more of the symbols involved is
+# replaceable. See gas pr 18561 and gcc pr 66609, 68178, etc.
+tryflag CFLAGS_AUTO -ffunction-sections
+tryflag CFLAGS_AUTO -fdata-sections
# On x86, make sure we don't have incompatible instruction set
# extensions enabled by default. This is bad for making static binaries.
# We cheat and use i486 rather than i386 because i386 really does not