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| author | H.J. Lu <hjl.tools@gmail.com> | 2015-10-15 05:23:42 -0700 |
|---|---|---|
| committer | H.J. Lu <hjl.tools@gmail.com> | 2015-10-15 05:23:58 -0700 |
| commit | 98ad631cd0a77205734abf4f2bb368a8560a08cf (patch) | |
| tree | 0c1c77ca47f7db8df6bf81395ad0d3d5ad91f82f /sysdeps/unix/sysv/linux/i386/libc-do-syscall.S | |
| parent | 83c01ab32b9aa7b27e4e88ed2969d14549e33c5c (diff) | |
| download | glibc-98ad631cd0a77205734abf4f2bb368a8560a08cf.tar.gz glibc-98ad631cd0a77205734abf4f2bb368a8560a08cf.tar.xz glibc-98ad631cd0a77205734abf4f2bb368a8560a08cf.zip | |
Optimize i386 syscall inlining for GCC 5
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.
Diffstat (limited to 'sysdeps/unix/sysv/linux/i386/libc-do-syscall.S')
| -rw-r--r-- | sysdeps/unix/sysv/linux/i386/libc-do-syscall.S | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/sysdeps/unix/sysv/linux/i386/libc-do-syscall.S b/sysdeps/unix/sysv/linux/i386/libc-do-syscall.S index af5c6f05a6..cdef3d5de1 100644 --- a/sysdeps/unix/sysv/linux/i386/libc-do-syscall.S +++ b/sysdeps/unix/sysv/linux/i386/libc-do-syscall.S @@ -18,6 +18,8 @@ #include <sysdep.h> +#if !__GNUC_PREREQ (5,0) + /* %eax, %ecx, %edx and %esi contain the values expected by the kernel. %edi points to a structure with the values of %ebx, %edi and %ebp. */ @@ -48,3 +50,4 @@ ENTRY (__libc_do_syscall) cfi_restore (ebx) ret END (__libc_do_syscall) +#endif |