path: root/libpthread/nptl/sysdeps
diff options
authorCarlos Santos <>2019-10-19 20:49:42 (GMT)
committerWaldemar Brodkorb <>2019-10-30 09:27:52 (GMT)
commit01e863c89fc772a406fe56c6dddb39f71a570c06 (patch)
tree197cdfb0f9abe789b04283fbaca010e1f5d4a502 /libpthread/nptl/sysdeps
parent3f1c2ffd2fd13c368b7652f4ee66d35f65d3f369 (diff)
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 <>
Diffstat (limited to 'libpthread/nptl/sysdeps')
1 files changed, 2 insertions, 2 deletions
diff --git a/libpthread/nptl/sysdeps/unix/sysv/linux/__syscall_error.c b/libpthread/nptl/sysdeps/unix/sysv/linux/__syscall_error.c
index 5e109a8..af26cf6 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)
return -1;