Messages in this thread Patch in this message | | | From | Ammar Faizi <> | Subject | [PATCH v1 06/11] tools/nolibc: i386: Implement syscall with 6 arguments | Date | Thu, 24 Mar 2022 14:30:34 +0700 |
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On i386, the 6th argument of syscall goes in %ebp. However, both Clang and GCC cannot use %ebp in the clobber list and in the "r" constraint without using -fomit-frame-pointer. To make it always available for any kind of compilation, the below workaround is implemented.
1) Push the 6-th argument. 2) Push %ebp. 3) Load the 6-th argument from 4(%esp) to %ebp. 4) Do the syscall (int $0x80). 5) Pop %ebp (restore the old value of %ebp). 6) Add %esp by 4 (undo the stack pointer).
Cc: x86@kernel.org Cc: llvm@lists.linux.dev Link: https://lore.kernel.org/lkml/2e335ac54db44f1d8496583d97f9dab0@AcuMS.aculab.com Suggested-by: David Laight <David.Laight@ACULAB.COM> Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org> ---
@@ Changelog:
Link RFC v2: https://lore.kernel.org/lkml/20220322102115.186179-4-ammarfaizi2@gnuweeb.org RFC v2 -> v1: - Use the same pattern for syscall6, regardless using GCC or Clang (comment from David). - Use appropriate constraints for syscall6 instead of always using register variables (comment from David).
Link RFC v1: https://lore.kernel.org/llvm/20220320093750.159991-4-ammarfaizi2@gnuweeb.org RFC v1 -> RFC v2: - Fix %ebp saving method. Don't use redzone, i386 doesn't have a redzone (comment from David and Alviro). --- tools/include/nolibc/arch-i386.h | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+)
diff --git a/tools/include/nolibc/arch-i386.h b/tools/include/nolibc/arch-i386.h index 6eb96ee8c4f7..cdffd99664ae 100644 --- a/tools/include/nolibc/arch-i386.h +++ b/tools/include/nolibc/arch-i386.h @@ -145,6 +145,29 @@ struct sys_stat_struct { _ret; \ }) +#define my_syscall6(num, arg1, arg2, arg3, arg4, arg5, arg6) \ +({ \ + long _eax = (long)(num); \ + long _arg6 = (long)(arg6); /* Always in memory */ \ + __asm__ volatile ( \ + "pushl %[_arg6]\n\t" \ + "pushl %%ebp\n\t" \ + "movl 4(%%esp),%%ebp\n\t" \ + "int $0x80\n\t" \ + "popl %%ebp\n\t" \ + "addl $4,%%esp\n\t" \ + : "+a"(_eax) /* %eax */ \ + : "b"(arg1), /* %ebx */ \ + "c"(arg2), /* %ecx */ \ + "d"(arg3), /* %edx */ \ + "S"(arg4), /* %esi */ \ + "D"(arg5), /* %edi */ \ + [_arg6]"m"(_arg6) /* memory */ \ + : "memory", "cc" \ + ); \ + _eax; \ +}) + /* startup code */ /* * i386 System V ABI mandates: -- Ammar Faizi
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