i386: Add <startup.h> [BZ #21913]

On Linux/i386, there are 3 ways to make a system call:

1. call *%gs:SYSINFO_OFFSET.  This requires TLS initialization.
2. call *_dl_sysinfo.  This requires relocation of _dl_sysinfo.
3. int $0x80.  This is slower than #2 and #3, but works everywhere.

When an object file is compiled with PIC, #1 is prefered since it is
faster than #3 and doesn't require relocation of _dl_sysinfo.  For
dynamic executables, ld.so initializes TLS.  However, for static
executables, before TLS is initialized by __libc_setup_tls, #3 should
be used for system calls.

This patch adds <startup.h> which defines _startup_fatal and defaults
it to __libc_fatal.  It replaces __libc_fatal with _startup_fatal in
static executables where it is called before __libc_setup_tls is called.
This header file is included in all files containing functions which are
called before __libc_setup_tls is called.  On Linux/i386, when PIE is
enabled by default, _startup_fatal is turned into ABORT_INSTRUCTION and
I386_USE_SYSENTER is defined to 0 so that "int $0x80" is used for system
calls before __libc_setup_tls is called.

Tested on i686 and x86-64.  Without this patch, all statically-linked
tests will fail on i686 when the compiler defaults to -fPIE.

	[BZ #21913]
	* csu/libc-tls.c: Include <startup.h> first.
	(__libc_setup_tls): Call _startup_fatal instead of __libc_fatal.
	* elf/dl-tunables.c: Include <startup.h> first.
	* include/libc-symbols.h (BUILD_PIE_DEFAULT): New.
	* sysdeps/generic/startup.h: New file.
	* sysdeps/unix/sysv/linux/i386/startup.h: Likewise.
	* sysdeps/unix/sysv/linux/i386/brk.c [BUILD_PIE_DEFAULT != 0]
	(I386_USE_SYSENTER): New.  Defined to 0.

1 files changed, 8 insertions, 0 deletions

diff --git a/include/libc-symbols.h b/include/libc-symbols.h
index 3310e3a678..fe3ab81c51 100644
--- a/include/libc-symbols.h
+++ b/include/libc-symbols.h
@@ -84,6 +84,14 @@
 
 #include <config.h>
 
+/* When PIC is defined and SHARED isn't defined, we are building PIE
+   by default.  */
+#if defined PIC && !defined SHARED
+# define BUILD_PIE_DEFAULT 1
+#else
+# define BUILD_PIE_DEFAULT 0
+#endif
+
 /* Define this for the benefit of portable GNU code that wants to check it.
    Code that checks with #if will not #include <config.h> again, since we've
    already done it (and this file is implicitly included in every compile,