diff mbox series

[2/2] i386: Always use __libc_do_syscall for 6-argument syscalls (bug 27997)

Message ID 10618fa43399978f066fb375fdf9732d333da925.1641895400.git.fweimer@redhat.com
State Superseded
Headers show
Series Remove some i386 system call optimizations | expand

Checks

Context Check Description
dj/TryBot-apply_patch success Patch applied to master at the time it was sent
dj/TryBot-32bit success Build for i686

Commit Message

Florian Weimer Jan. 11, 2022, 10:06 a.m. UTC
The CAN_USE_REGISTER_ASM_EBP optimization was unreliable because
the configure-time check did not match how %ebp was used during
the build.  With GCC 12, autovectorization at -O2, and the need
for -mstackrealign for compatibility with legacy binaries, the check
is increasingly problematic: CAN_USE_REGISTER_ASM_EBP is set to 1,
but glibc cannot be built with this optimization.
---
 config.h.in                               |  4 ---
 sysdeps/unix/sysv/linux/i386/configure    | 39 -----------------------
 sysdeps/unix/sysv/linux/i386/configure.ac | 17 ----------
 sysdeps/unix/sysv/linux/i386/sysdep.h     | 34 +++-----------------
 4 files changed, 4 insertions(+), 90 deletions(-)
diff mbox series

Patch

diff --git a/config.h.in b/config.h.in
index 82ade1cec4..ff8597413d 100644
--- a/config.h.in
+++ b/config.h.in
@@ -277,10 +277,6 @@ 
 /* Define if static PIE is enabled.  */
 #define ENABLE_STATIC_PIE 0
 
-/* Some compiler options may now allow to use ebp in __asm__ (used mainly
-   in i386 6 argument syscall issue).  */
-#define CAN_USE_REGISTER_ASM_EBP 0
-
 /* The default value of x86 CET control.  */
 #define DEFAULT_DL_X86_CET_CONTROL cet_elf_property
 
diff --git a/sysdeps/unix/sysv/linux/i386/configure b/sysdeps/unix/sysv/linux/i386/configure
index 0327590486..f119e62fc3 100644
--- a/sysdeps/unix/sysv/linux/i386/configure
+++ b/sysdeps/unix/sysv/linux/i386/configure
@@ -1,44 +1,5 @@ 
 # This file is generated from configure.ac by Autoconf.  DO NOT EDIT!
  # Local configure fragment for sysdeps/unix/sysv/linux/i386.
 
-# Check if CFLAGS allows compiler to use ebp register in inline assembly.
-
-{ $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler flags allows ebp in inline assembly" >&5
-$as_echo_n "checking if compiler flags allows ebp in inline assembly... " >&6; }
-if ${libc_cv_can_use_register_asm_ebp+:} false; then :
-  $as_echo_n "(cached) " >&6
-else
-
-cat confdefs.h - <<_ACEOF >conftest.$ac_ext
-/* end confdefs.h.  */
-
-    void foo (int i)
-    {
-      register int reg asm ("ebp") = i;
-      asm ("# %0" : : "r" (reg));
-    }
-int
-main ()
-{
-
-  ;
-  return 0;
-}
-_ACEOF
-if ac_fn_c_try_compile "$LINENO"; then :
-  libc_cv_can_use_register_asm_ebp=yes
-else
-  libc_cv_can_use_register_asm_ebp=no
-fi
-rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
-
-fi
-{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_can_use_register_asm_ebp" >&5
-$as_echo "$libc_cv_can_use_register_asm_ebp" >&6; }
-if test $libc_cv_can_use_register_asm_ebp = yes; then
-  $as_echo "#define CAN_USE_REGISTER_ASM_EBP 1" >>confdefs.h
-
-fi
-
 libc_cv_gcc_unwind_find_fde=yes
 ldd_rewrite_script=sysdeps/unix/sysv/linux/ldd-rewrite.sed
diff --git a/sysdeps/unix/sysv/linux/i386/configure.ac b/sysdeps/unix/sysv/linux/i386/configure.ac
index 9e980784bb..64ab2cc2c8 100644
--- a/sysdeps/unix/sysv/linux/i386/configure.ac
+++ b/sysdeps/unix/sysv/linux/i386/configure.ac
@@ -1,22 +1,5 @@ 
 GLIBC_PROVIDES dnl See aclocal.m4 in the top level source directory.
 # Local configure fragment for sysdeps/unix/sysv/linux/i386.
 
-# Check if CFLAGS allows compiler to use ebp register in inline assembly.
-AC_CACHE_CHECK([if compiler flags allows ebp in inline assembly],
-                libc_cv_can_use_register_asm_ebp, [
-AC_COMPILE_IFELSE(
-  [AC_LANG_PROGRAM([
-    void foo (int i)
-    {
-      register int reg asm ("ebp") = i;
-      asm ("# %0" : : "r" (reg));
-    }])],
-  [libc_cv_can_use_register_asm_ebp=yes],
-  [libc_cv_can_use_register_asm_ebp=no])
-])
-if test $libc_cv_can_use_register_asm_ebp = yes; then
-  AC_DEFINE(CAN_USE_REGISTER_ASM_EBP)
-fi
-
 libc_cv_gcc_unwind_find_fde=yes
 ldd_rewrite_script=sysdeps/unix/sysv/linux/ldd-rewrite.sed
diff --git a/sysdeps/unix/sysv/linux/i386/sysdep.h b/sysdeps/unix/sysv/linux/i386/sysdep.h
index fcd78e3157..4558ab66cb 100644
--- a/sysdeps/unix/sysv/linux/i386/sysdep.h
+++ b/sysdeps/unix/sysv/linux/i386/sysdep.h
@@ -42,15 +42,6 @@ 
 # endif
 #endif
 
-/* Since GCC 5 and above can properly spill %ebx with PIC when needed,
-   we can inline syscalls with 6 arguments if GCC 5 or above is used
-   to compile glibc.  Disable GCC 5 optimization when compiling for
-   profiling or when -fno-omit-frame-pointer is used since asm ("ebp")
-   can't be used to put the 6th argument in %ebp for syscall.  */
-#if !defined PROF && CAN_USE_REGISTER_ASM_EBP
-# define OPTIMIZE_FOR_GCC_5
-#endif
-
 #ifdef __ASSEMBLER__
 
 /* Linux uses a negative return value to indicate syscall errors,
@@ -238,7 +229,6 @@ 
 extern int __syscall_error (int)
   attribute_hidden __attribute__ ((__regparm__ (1)));
 
-#ifndef OPTIMIZE_FOR_GCC_5
 /* Six-argument syscalls use an out-of-line helper, because an inline
    asm using all registers apart from %esp cannot work reliably and
    the assembler does not support describing an asm that saves and
@@ -249,7 +239,6 @@  struct libc_do_syscall_args
 {
   int ebx, edi, ebp;
 };
-#endif
 
 # define VDSO_NAME  "LINUX_2.6"
 # define VDSO_HASH  61765110
@@ -302,14 +291,8 @@  struct libc_do_syscall_args
 
 /* Each object using 6-argument inline syscalls must include a
    definition of __libc_do_syscall.  */
-#ifdef OPTIMIZE_FOR_GCC_5
-# define INTERNAL_SYSCALL_MAIN_6(name, args...) \
-    INTERNAL_SYSCALL_MAIN_INLINE(name, 6, args)
-# define INTERNAL_SYSCALL_MAIN_NCS_6(name, args...) \
-    INTERNAL_SYSCALL_MAIN_NCS(name, 6, args)
-#else /* GCC 5  */
-# define INTERNAL_SYSCALL_MAIN_6(name, arg1, arg2, arg3,		\
-				 arg4, arg5, arg6)			\
+#define INTERNAL_SYSCALL_MAIN_6(name, arg1, arg2, arg3,			\
+				arg4, arg5, arg6)			\
   struct libc_do_syscall_args _xv =					\
     {									\
       (int) (arg1),							\
@@ -322,8 +305,8 @@  struct libc_do_syscall_args
     : "=a" (resultvar)							\
     : "i" (__NR_##name), "c" (arg2), "d" (arg3), "S" (arg4), "D" (&_xv) \
     : "memory", "cc")
-# define INTERNAL_SYSCALL_MAIN_NCS_6(name, arg1, arg2, arg3,		\
-				     arg4, arg5, arg6)			\
+#define INTERNAL_SYSCALL_MAIN_NCS_6(name, arg1, arg2, arg3,		\
+				    arg4, arg5, arg6)			\
   struct libc_do_syscall_args _xv =					\
     {									\
       (int) (arg1),							\
@@ -336,7 +319,6 @@  struct libc_do_syscall_args
     : "=a" (resultvar)							\
     : "a" (name), "c" (arg2), "d" (arg3), "S" (arg4), "D" (&_xv)	\
     : "memory", "cc")
-#endif /* GCC 5  */
 
 #define INTERNAL_SYSCALL(name, nr, args...) \
   ({									      \
@@ -417,14 +399,6 @@  struct libc_do_syscall_args
 #define ASMARGS_5(arg1, arg2, arg3, arg4, arg5) \
 	ASMARGS_4 (arg1, arg2, arg3, arg4), "D" ((unsigned int) (arg5))
 
-#ifdef OPTIMIZE_FOR_GCC_5
-# define LOADREGS_6(arg1, arg2, arg3, arg4, arg5, arg6) \
-	register unsigned int _a6 asm ("ebp") = (unsigned int) (arg6); \
-	LOADREGS_5 (arg1, arg2, arg3, arg4, arg5)
-# define ASMARGS_6(arg1, arg2, arg3, arg4, arg5, arg6) \
-	ASMARGS_5 (arg1, arg2, arg3, arg4, arg5), "r" (_a6)
-#endif /* GCC 5  */
-
 #define ASMFMT_0()
 #ifdef __PIC__
 # define ASMFMT_1(arg1) \