[Buildroot] [PATCH/next v2 2/2] gcc: remove BR2_GCC_ENABLE_TLS option
Thomas Petazzoni
thomas.petazzoni at free-electrons.com
Tue Aug 30 21:33:28 UTC 2016
The current BR2_GCC_ENABLE_TLS can cause users to make incorrect
choices, and is not very useful. This options allows to decide whether
we pass --enable-tls or --disable-tls to gcc, to enable or disable
support for Thread Local Storage.
Its behavior is:
- The option is default to "y" but only exists if we're using
uClibc/NPTL or glibc.
- When we're using uClibc, the option can be disabled.
So, in practice, this means that currently:
- TLS support is always on for glibc
- TLS support is on by default for uClibc/NPTL, but can be disabled in
the configuration. This is in fact bad and causes the build failure
reported in bug #7424 (this bug is still reproducible on master)
- TLS support is always disabled for uClibc/no-thread and
uClibc/linuxthreads.
- TLS support is always disabled for musl. This does not cause any
build failure, but musl can use TLS support, and therefore be more
efficient. According to
http://www.openwall.com/lists/musl/2012/10/04/1, "Note that if you've
been building gcc with --disable-tls, __thread was already working
but gets emulated (very poorly; it's slow and will abort() if it runs
out of memory) through libgcc.".
So, this commit completely removes the BR2_GCC_ENABLE_TLS and instead
makes the right choice inside gcc.mk directly:
- TLS support enabled for glibc, musl and uClibc/NPTL
- TLS support in other cases, i.e uClibc/no-thread and
uClibc/linuxthreads.
We have intentionally *not* added the option to
Config.in.legacy. Indeed, the new behavior is *exactly* the same as the
older behavior, with the exception of:
- People can no longer disable TLS support in uClibc/NPTL, which was
anyway causing a build failure and therefore was not used.
- TLS support is now enabled on musl, but people using musl already had
BR2_GCC_ENABLE_TLS not set, so they wouldn't get the legacy warning.
Fixes bug #7424.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni at free-electrons.com>
---
Changes since v1:
- Invert the condition logic, to make it simpler. Suggested by Arnout.
---
package/gcc/Config.in.host | 8 --------
package/gcc/gcc.mk | 9 ++++++---
2 files changed, 6 insertions(+), 11 deletions(-)
diff --git a/package/gcc/Config.in.host b/package/gcc/Config.in.host
index 37728e0..8ed946b 100644
--- a/package/gcc/Config.in.host
+++ b/package/gcc/Config.in.host
@@ -148,14 +148,6 @@ config BR2_TOOLCHAIN_BUILDROOT_FORTRAN
Fortran language and you want Fortran libraries to be
installed on your target system.
-config BR2_GCC_ENABLE_TLS
- bool "Enable compiler tls support" if BR2_TOOLCHAIN_BUILDROOT_UCLIBC
- default y
- depends on BR2_PTHREADS_NATIVE || BR2_TOOLCHAIN_BUILDROOT_GLIBC
- help
- Enable the compiler to generate code for accessing
- thread local storage variables
-
config BR2_GCC_ENABLE_LTO
bool "Enable compiler link-time-optimization support"
select BR2_BINUTILS_ENABLE_LTO
diff --git a/package/gcc/gcc.mk b/package/gcc/gcc.mk
index 39c3eeb..82050b4 100644
--- a/package/gcc/gcc.mk
+++ b/package/gcc/gcc.mk
@@ -133,10 +133,13 @@ ifeq ($(BR2_sparc)$(BR2_sparc64),y)
HOST_GCC_COMMON_CONF_OPTS += --disable-libsanitizer
endif
-ifeq ($(BR2_GCC_ENABLE_TLS),y)
-HOST_GCC_COMMON_CONF_OPTS += --enable-tls
-else
+# TLS support is not needed on uClibc/no-thread and
+# uClibc/linux-threads, otherwise, for all other situations (glibc,
+# musl and uClibc/NPTL), we need it.
+ifeq ($(BR2_TOOLCHAIN_BUILDROOT_UCLIBC)$(BR2_PTHREADS)$(BR2_PTHREADS_NONE),yy)
HOST_GCC_COMMON_CONF_OPTS += --disable-tls
+else
+HOST_GCC_COMMON_CONF_OPTS += --enable-tls
endif
ifeq ($(BR2_GCC_ENABLE_LTO),y)
--
2.7.4
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