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Re: [PATCH] Rework -fno-omit-frame-pointer support on i386

From: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>
To: "H.J. Lu" <hjl dot tools at gmail dot com>
Cc: GNU C Library <libc-alpha at sourceware dot org>
Date: Fri, 17 Feb 2017 12:47:55 -0200
Subject: Re: [PATCH] Rework -fno-omit-frame-pointer support on i386
Authentication-results: sourceware.org; auth=none
References: <1483966550-21038-1-git-send-email-adhemerval.zanella@linaro.org> <CAMe9rOpsn6_y3MY6X=j-L7FncmWdkoQkQazvxRQUz=W_msRCeQ@mail.gmail.com>

On 16/02/2017 17:24, H.J. Lu wrote:
> On Mon, Jan 9, 2017 at 4:55 AM, Adhemerval Zanella
>> +# Check if CFLAGS sets -fno-omit-frame-pointer
>> +AC_CACHE_CHECK(for if compiler flags sets -fno-omit-frame-pointer,
>> +              libc_cv_no_omit_frame_pointer,
>> +              [cat > conftest.c << EOF
>> +              void foo (void) { }
>> +EOF
>> +              libc_cv_no_omit_frame_pointer=no
>> +              if AC_TRY_COMMAND(${CC-cc} $CFLAGS -S conftest.c -o conftest.s 1>&AS_MESSAGE_LOG_FD); then
>> +                if grep 'push.*%ebp' conftest.s >/dev/null &&
>> +                   grep 'pop.*%ebp' conftest.s >/dev/null; then
>> +                  libc_cv_no_omit_frame_pointer=yes
>> +                fi
>> +              fi
>> +              rm -f conftest.c conftest.s
>> +              ])
> 
> I prefer something like
> 
> [hjl@gnu-fer something like
> 
> [hjl@gnu-6 tmp]$ cat ebp.c
> void
> foo (int i)
> {
>   register int reg asm ("ebp") = i;
>   asm ("# %0" : : "r" (reg));
> }
> [hjl@gnu-6 tmp]$ gcc -S -m32 -Os ebp.c
> ebp.c: In function ‘foo’:
> ebp.c:6:1: error: bp cannot be used in asm here
>  }
>  ^
> [hjl@gnu-6 tmp]$ gcc -S -m32 -O2 ebp.c
> [hjl@gnu-6 tmp]$
> 
>> +if test $libc_cv_no_omit_frame_pointer = yes; then
>> +  AC_DEFINE(NO_OMIT_FRAME_POINTER)
>> +fi
> 
> How about something like CAN_USE_REGISTER_ASM_EBP?

I implemented both your suggestions in this version:

	[BZ #21029]
	* config.h.in [CAN_USE_REGISTER_ASM_EBP]: New define.
	* sysdeps/unix/sysv/linux/i386/Makefile
	[$(subdir) = elf] (sysdep-dl-routines): Add libc-do-syscall.
	(uses-6-syscall-arguments): Remove.
	[$(subdir) = misc] (CFLAGS-epoll_pwait.o): Likewise.
	[$(subdir) = misc] (CFLAGS-epoll_pwait.os): Likewise.
	[$(subdir) = misc] (CFLAGS-mmap.o): Likewise.
	[$(subdir) = misc] (CFLAGS-mmap.os): Likewise.
	[$(subdir) = misc] (CFLAGS-mmap64.o): Likewise.
	[$(subdir) = misc] (CFLAGS-mmap64.os): Likewise.
	[$(subdir) = misc] (CFLAGS-pselect.o): Likewise.
	[$(subdir) = misc] (cflags-pselect.o): Likewise.
	[$(subdir) = misc] (cflags-pselect.os): Likewise.
	[$(subdir) = misc] (cflags-rtld-mmap.os): Likewise.
	[$(subdir) = sysvipc] (cflags-semtimedop.o): Likewise.
	[$(subdir) = sysvipc] (cflags-semtimedop.os): Likewise.
	[$(subdir) = io] (CFLAGS-posix_fadvise64.o): Likewise.
	[$(subdir) = io] (CFLAGS-posix_fadvise64.os): Likewise.
	[$(subdir) = io] (CFLAGS-posix_fallocate.o): Likewise.
	[$(subdir) = io] (CFLAGS-posix_fallocate.os): Likewise.
	[$(subdir) = io] (CFLAGS-posix_fallocate64.o): Likewise.
	[$(subdir) = io] (CFLAGS-posix_fallocate64.os): Likewise.
	[$(subdir) = io] (CFLAGS-sync_file_range.o): Likewise.
	[$(subdir) = io] (CFLAGS-sync_file_range.os): Likewise.
	[$(subdir) = io] (CFLAGS-fallocate.o): Likewise.
	[$(subdir) = io] (CFLAGS-fallocate.os): Likewise.
	[$(subdir) = io] (CFLAGS-fallocate64.o): Likewise.
	[$(subdir) = io] (CFLAGS-fallocate64.os): Likewise.
	[$(subdir) = nptl] (CFLAGS-pthread_rwlock_timedrdlock.o):
	Likewise.
	[$(subdir) = nptl] (CFLAGS-pthread_rwlock_timedrdlock.os):
	Likewise.
	[$(subdir) = nptl] (CFLAGS-pthread_rwlock_timedrwlock.o):
	Likewise.
	[$(subdir) = nptl] (CFLAGS-pthread_rwlock_timedrwlock.os):
	Likewise.
	[$(subdir) = nptl] (CFLAGS-sem_wait.o): Likewise.
	[$(subdir) = nptl] (CFLAGS-sem_wait.os): Likewise.
	[$(subdir) = nptl] (CFLAGS-sem_timedwait.o): Likewise.
	[$(subdir) = nptl] (CFLAGS-sem_timedwait.os): Likewise.
	* sysdeps/unix/sysv/linux/i386/configure.ac: Add check if compiler allows
	ebp on inline assembly.
	* sysdeps/unix/sysv/linux/i386/configure: Regenerate.
	* sysdeps/unix/sysv/linux/i386/sysdep.h (OPTIMIZE_FOR_GCC_5):
	Set if CAN_USE_REGISTER_ASM_EBP is set.
	(check_consistency): Likewise.
---

diff --git a/config.h.in b/config.h.in
index 7bfe923..fb2cc51 100644
--- a/config.h.in
+++ b/config.h.in
@@ -259,4 +259,8 @@
 /* Build glibc with tunables support.  */
 #define HAVE_TUNABLES 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
+
 #endif
diff --git a/sysdeps/unix/sysv/linux/i386/Makefile b/sysdeps/unix/sysv/linux/i386/Makefile
index 9609752..6aac0df 100644
--- a/sysdeps/unix/sysv/linux/i386/Makefile
+++ b/sysdeps/unix/sysv/linux/i386/Makefile
@@ -1,47 +1,18 @@
 # The default ABI is 32.
 default-abi := 32
 
-# %ebp is used to pass the 6th argument to system calls, so these
-# system calls are incompatible with a frame pointer.
-uses-6-syscall-arguments = -fomit-frame-pointer
-
 ifeq ($(subdir),misc)
 sysdep_routines += ioperm iopl vm86
-CFLAGS-epoll_pwait.o += $(uses-6-syscall-arguments)
-CFLAGS-epoll_pwait.os += $(uses-6-syscall-arguments)
-CFLAGS-mmap.o += $(uses-6-syscall-arguments)
-CFLAGS-mmap.os += $(uses-6-syscall-arguments)
-CFLAGS-mmap64.o += $(uses-6-syscall-arguments)
-CFLAGS-mmap64.os += $(uses-6-syscall-arguments)
-CFLAGS-pselect.o += $(uses-6-syscall-arguments)
-CFLAGS-pselect.os += $(uses-6-syscall-arguments)
-CFLAGS-rtld-mmap.os += $(uses-6-syscall-arguments)
-endif
-
-ifeq ($(subdir),sysvipc)
-CFLAGS-semtimedop.o += $(uses-6-syscall-arguments)
-CFLAGS-semtimedop.os += $(uses-6-syscall-arguments)
 endif
 
 ifeq ($(subdir),elf)
+sysdep-dl-routines += libc-do-syscall
 sysdep-others += lddlibc4
 install-bin += lddlibc4
 endif
 
 ifeq ($(subdir),io)
 sysdep_routines += libc-do-syscall
-CFLAGS-posix_fadvise64.o += $(uses-6-syscall-arguments)
-CFLAGS-posix_fadvise64.os += $(uses-6-syscall-arguments)
-CFLAGS-posix_fallocate.o += $(uses-6-syscall-arguments)
-CFLAGS-posix_fallocate.os += $(uses-6-syscall-arguments)
-CFLAGS-posix_fallocate64.o += $(uses-6-syscall-arguments)
-CFLAGS-posix_fallocate64.os += $(uses-6-syscall-arguments)
-CFLAGS-sync_file_range.o += $(uses-6-syscall-arguments)
-CFLAGS-sync_file_range.os += $(uses-6-syscall-arguments)
-CFLAGS-fallocate.o += $(uses-6-syscall-arguments)
-CFLAGS-fallocate.os += $(uses-6-syscall-arguments)
-CFLAGS-fallocate64.o += $(uses-6-syscall-arguments)
-CFLAGS-fallocate64.os += $(uses-6-syscall-arguments)
 endif
 
 ifeq ($(subdir),nptl)
@@ -61,14 +32,6 @@ ifeq ($(subdir),nptl)
 # pull in __syscall_error routine
 libpthread-routines += sysdep
 libpthread-shared-only-routines += sysdep
-CFLAGS-pthread_rwlock_timedrdlock.o += $(uses-6-syscall-arguments)
-CFLAGS-pthread_rwlock_timedrdlock.os += $(uses-6-syscall-arguments)
-CFLAGS-pthread_rwlock_timedwrlock.o += $(uses-6-syscall-arguments)
-CFLAGS-pthread_rwlock_timedwrlock.os += $(uses-6-syscall-arguments)
-CFLAGS-sem_wait.o += $(uses-6-syscall-arguments)
-CFLAGS-sem_wait.os += $(uses-6-syscall-arguments)
-CFLAGS-sem_timedwait.o += $(uses-6-syscall-arguments)
-CFLAGS-sem_timedwait.os += $(uses-6-syscall-arguments)
 endif
 
 ifeq ($(subdir),rt)
diff --git a/sysdeps/unix/sysv/linux/i386/configure b/sysdeps/unix/sysv/linux/i386/configure
index eb72659..ae2c356 100644
--- a/sysdeps/unix/sysv/linux/i386/configure
+++ b/sysdeps/unix/sysv/linux/i386/configure
@@ -3,5 +3,44 @@
 
 arch_minimum_kernel=2.6.32
 
+# 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 1a11da6..1cd632e 100644
--- a/sysdeps/unix/sysv/linux/i386/configure.ac
+++ b/sysdeps/unix/sysv/linux/i386/configure.ac
@@ -3,5 +3,22 @@ GLIBC_PROVIDES dnl See aclocal.m4 in the top level source directory.
 
 arch_minimum_kernel=2.6.32
 
+# 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 baf4642..c40db59 100644
--- a/sysdeps/unix/sysv/linux/i386/sysdep.h
+++ b/sysdeps/unix/sysv/linux/i386/sysdep.h
@@ -44,9 +44,9 @@
 /* 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 since asm ("ebp") can't be used to put the 6th argument
-   in %ebp for syscall.  */
-#if __GNUC_PREREQ (5,0) && !defined PROF
+   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 __GNUC_PREREQ (5,0) && !defined PROF && CAN_USE_REGISTER_ASM_EBP
 # define OPTIMIZE_FOR_GCC_5
 #endif
 
@@ -611,7 +611,8 @@ struct libc_do_syscall_args
 #endif
 
 /* Consistency check for position-independent code.  */
-#if defined __PIC__ && !defined OPTIMIZE_FOR_GCC_5
+#if defined __PIC__ && !defined OPTIMIZE_FOR_GCC_5 \
+    && !CAN_USE_REGISTER_ASM_EBP
 # define check_consistency()						      \
   ({ int __res;								      \
      __asm__ __volatile__						      \
-- 
2.7.4
Follow-Ups:
- Re: [PATCH] Rework -fno-omit-frame-pointer support on i386
  - From: H.J. Lu
References:
- Re: [PATCH] Rework -fno-omit-frame-pointer support on i386
  - From: H.J. Lu
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