From 01e863c89fc772a406fe56c6dddb39f71a570c06 Mon Sep 17 00:00:00 2001 From: Carlos Santos Date: Sat, 19 Oct 2019 17:49:42 -0300 Subject: Make __syscall_error return long, as expected by syscall() callers The return type of syscall() is long so __syscall_error, which is jumped to by syscall handlers to stash an error number into errno, must return long too otherwhise it returs 4294967295L instead of -1L. For example, syscall for x86_64 is defined in libc/sysdeps/linux/x86_64/syscall.S as syscall: movq %rdi, %rax /* Syscall number -> rax. */ movq %rsi, %rdi /* shift arg1 - arg5. */ movq %rdx, %rsi movq %rcx, %rdx movq %r8, %r10 movq %r9, %r8 movq 8(%rsp),%r9 /* arg6 is on the stack. */ syscall /* Do the system call. */ cmpq $-4095, %rax /* Check %rax for error. */ jae __syscall_error /* Branch forward if it failed. */ ret /* Return to caller. */ In libc/sysdeps/linux/x86_64/__syscall_error.c, __syscall_error is defined as int __syscall_error(void) attribute_hidden; int __syscall_error(void) { register int err_no __asm__ ("%rcx"); __asm__ ("mov %rax, %rcx\n\t" "neg %rcx"); __set_errno(err_no); return -1; } So __syscall_error returns -1 as a 32-bit int in a 64-bit register, %rax (0x00000000ffffffff, whose decimal value is decimal 4294967295) and a test like this always returns false: if (syscall(number, ...) == -1) foo(); Fix the error by making __syscall_error return a long, like syscall(). The problem can be circumvented by the caller by coercing the returned value to int before comparing it to -1: if ((int) syscall(number, ...) == -1) foo(); The same problem probably occurs on other 64-bit systems but so far only x86_64 was tested, so this change must be considered experimental. Signed-off-by: Carlos Santos --- libpthread/nptl/sysdeps/unix/sysv/linux/__syscall_error.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'libpthread/nptl/sysdeps/unix') diff --git a/libpthread/nptl/sysdeps/unix/sysv/linux/__syscall_error.c b/libpthread/nptl/sysdeps/unix/sysv/linux/__syscall_error.c index 5e109a83b..af26cf6ab 100644 --- a/libpthread/nptl/sysdeps/unix/sysv/linux/__syscall_error.c +++ b/libpthread/nptl/sysdeps/unix/sysv/linux/__syscall_error.c @@ -10,8 +10,8 @@ /* This routine is jumped to by all the syscall handlers, to stash * an error number into errno. */ -int __syscall_error(int err_no) attribute_hidden; -int __syscall_error(int err_no) +long __syscall_error(int err_no) attribute_hidden; +long __syscall_error(int err_no) { __set_errno(err_no); return -1; -- cgit v1.2.3