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Since GCC 5 and above can properly spill %ebx when needed, we can inline syscalls with 6 arguments if GCC 5 or above is used to compile glibc. This patch rewrites INTERNAL_SYSCALL macros and skips __libc_do_syscall for GCC 5. For sysdeps/unix/sysv/linux/i386/brk.c, with -O2 -march=i686 -mtune=generic, GCC 5.2 now generates: <__brk>: 0: push %ebx 1: mov $0x2d,%eax 6: mov 0x8(%esp),%ebx a: call b <__brk+0xb> b: R_386_PC32 __x86.get_pc_thunk.dx f: add $0x2,%edx 11: R_386_GOTPC _GLOBAL_OFFSET_TABLE_ 15: call *%gs:0x10 1c: mov 0x0(%edx),%edx 1e: R_386_GOT32 __curbrk 22: cmp %eax,%ebx 24: mov %eax,(%edx) 26: ja 30 <__brk+0x30> 28: xor %eax,%eax 2a: pop %ebx 2b: ret instead of <__brk>: 0: push %ebx 1: mov 0x8(%esp),%ecx 5: call 6 <__brk+0x6> 6: R_386_PC32 __x86.get_pc_thunk.bx a: add $0x2,%ebx c: R_386_GOTPC _GLOBAL_OFFSET_TABLE_ 10: xchg %ecx,%ebx 12: mov $0x2d,%eax 17: call *%gs:0x10 1e: xchg %ecx,%ebx 20: mov %eax,%edx 22: mov 0x0(%ebx),%eax 24: R_386_GOT32 __curbrk 28: mov %edx,(%eax) 2a: xor %eax,%eax 2c: cmp %edx,%ecx 2e: ja 38 <__brk+0x38> 30: pop %ebx 31: ret The new one is shorter by 2 instructions. * sysdeps/unix/sysv/linux/i386/libc-do-syscall.S (__libc_do_syscall): Defined only if !__GNUC_PREREQ (5,0). * sysdeps/unix/sysv/linux/i386/sysdep.h: Define assembler macros only if !__GNUC_PREREQ (5,0). (INTERNAL_SYSCALL_MAIN_6): Optimize for GCC 5. (INTERNAL_SYSCALL_MAIN_INLINE): Likewise. (INTERNAL_SYSCALL_NCS): Likewise. (LOADREGS_0): New macro for GCC 5. (ASMARGS_0): Likewise. (LOADREGS_1): Likewise. (ASMARGS_1): Likewise. (LOADREGS_2): Likewise. (ASMARGS_2): Likewise. (LOADREGS_3): Likewise. (ASMARGS_3): Likewise. (LOADREGS_4): Likewise. (ASMARGS_4): Likewise. (LOADREGS_5): Likewise. (ASMARGS_5): Likewise. (LOADREGS_6): Likewise. (ASMARGS_6): Likewise.
This directory contains the sources of the GNU C Library. See the file "version.h" for what release version you have. The GNU C Library is the standard system C library for all GNU systems, and is an important part of what makes up a GNU system. It provides the system API for all programs written in C and C-compatible languages such as C++ and Objective C; the runtime facilities of other programming languages use the C library to access the underlying operating system. In GNU/Linux systems, the C library works with the Linux kernel to implement the operating system behavior seen by user applications. In GNU/Hurd systems, it works with a microkernel and Hurd servers. The GNU C Library implements much of the POSIX.1 functionality in the GNU/Hurd system, using configurations i[4567]86-*-gnu. The current GNU/Hurd support requires out-of-tree patches that will eventually be incorporated into an official GNU C Library release. When working with Linux kernels, this version of the GNU C Library requires Linux kernel version 2.6.32 or later. Also note that the shared version of the libgcc_s library must be installed for the pthread library to work correctly. The GNU C Library supports these configurations for using Linux kernels: aarch64*-*-linux-gnu alpha*-*-linux-gnu arm-*-linux-gnueabi hppa-*-linux-gnu Not currently functional without patches. i[4567]86-*-linux-gnu x86_64-*-linux-gnu Can build either x86_64 or x32 ia64-*-linux-gnu m68k-*-linux-gnu microblaze*-*-linux-gnu mips-*-linux-gnu mips64-*-linux-gnu powerpc-*-linux-gnu Hardware or software floating point, BE only. powerpc64*-*-linux-gnu Big-endian and little-endian. s390-*-linux-gnu s390x-*-linux-gnu sh[34]-*-linux-gnu sparc*-*-linux-gnu sparc64*-*-linux-gnu tilegx-*-linux-gnu tilepro-*-linux-gnu If you are interested in doing a port, please contact the glibc maintainers; see http://www.gnu.org/software/libc/ for more information. See the file INSTALL to find out how to configure, build, and install the GNU C Library. You might also consider reading the WWW pages for the C library at http://www.gnu.org/software/libc/. The GNU C Library is (almost) completely documented by the Texinfo manual found in the `manual/' subdirectory. The manual is still being updated and contains some known errors and omissions; we regret that we do not have the resources to work on the manual as much as we would like. For corrections to the manual, please file a bug in the `manual' component, following the bug-reporting instructions below. Please be sure to check the manual in the current development sources to see if your problem has already been corrected. Please see http://www.gnu.org/software/libc/bugs.html for bug reporting information. We are now using the Bugzilla system to track all bug reports. This web page gives detailed information on how to report bugs properly. The GNU C Library is free software. See the file COPYING.LIB for copying conditions, and LICENSES for notices about a few contributions that require these additional notices to be distributed. License copyright years may be listed using range notation, e.g., 1996-2015, indicating that every year in the range, inclusive, is a copyrightable year that would otherwise be listed individually.