[RFC v3 4/5] common-user: Adjust system call return on FreeBSD

[Warner Losh]

All the *-users generally use the negative errno return codes to signal
errno for a system call.  FreeBSD's system calls, on the other hand,
returns errno, not -errno. Add ifdefs for FreeBSD to make the adjustment
on the 4 hosts that we have support for.

Signed-off-by: Warner Losh <imp@bsdimp.com>
---
 common-user/host/aarch64/safe-syscall.inc.S | 8 ++++++++
 common-user/host/arm/safe-syscall.inc.S     | 7 +++++++
 common-user/host/i386/safe-syscall.inc.S    | 9 +++++++++
 common-user/host/x86_64/safe-syscall.inc.S  | 9 +++++++++
 4 files changed, 33 insertions(+)

diff --git a/common-user/host/aarch64/safe-syscall.inc.S 
b/common-user/host/aarch64/safe-syscall.inc.S
index bc1f5a9792..9f9525fe25 100644
--- a/common-user/host/aarch64/safe-syscall.inc.S
+++ b/common-user/host/aarch64/safe-syscall.inc.S
@@ -64,6 +64,14 @@ safe_syscall_start:
        svc     0x0
 safe_syscall_end:
        /* code path for having successfully executed the syscall */
+#ifdef __FreeBSD__
+        /*
+         * FreeBSD kernel returns C bit set with positive errno.
+         * Encode this for use in bsd-user as -errno:
+        *    x0 = !c ? x0 : -x0
+        */
+       csneg  x0, x0, x0, cc
+#endif
        ret
 
 0:
diff --git a/common-user/host/arm/safe-syscall.inc.S 
b/common-user/host/arm/safe-syscall.inc.S
index 88c4958504..459e5f87c2 100644
--- a/common-user/host/arm/safe-syscall.inc.S
+++ b/common-user/host/arm/safe-syscall.inc.S
@@ -78,6 +78,13 @@ safe_syscall_start:
        swi     0
 safe_syscall_end:
        /* code path for having successfully executed the syscall */
+#ifdef __FreeBSD__
+        /*
+         * FreeBSD kernel returns C bit set with positive errno.
+         * Encode this for use in bsd-user as -errno:
+         */
+        negcs   r0, r0
+#endif
        pop     { r4, r5, r6, r7, r8, pc }
 
 1:
diff --git a/common-user/host/i386/safe-syscall.inc.S 
b/common-user/host/i386/safe-syscall.inc.S
index 9e58fc6504..ba55a35e92 100644
--- a/common-user/host/i386/safe-syscall.inc.S
+++ b/common-user/host/i386/safe-syscall.inc.S
@@ -75,6 +75,15 @@ safe_syscall_start:
        int     $0x80
 safe_syscall_end:
        /* code path for having successfully executed the syscall */
+#ifdef __FreeBSD__
+        /*
+         * FreeBSD kernel returns C bit set with positive errno.
+         * Encode this for use in bsd-user as -errno:
+         */
+        jnb     2f
+        neg     %eax
+2:
+#endif
        pop     %ebx
        .cfi_remember_state
        .cfi_adjust_cfa_offset -4
diff --git a/common-user/host/x86_64/safe-syscall.inc.S 
b/common-user/host/x86_64/safe-syscall.inc.S
index f36992daa3..46c527e058 100644
--- a/common-user/host/x86_64/safe-syscall.inc.S
+++ b/common-user/host/x86_64/safe-syscall.inc.S
@@ -72,6 +72,15 @@ safe_syscall_start:
         syscall
 safe_syscall_end:
         /* code path for having successfully executed the syscall */
+#ifdef __FreeBSD__
+        /*
+         * FreeBSD kernel returns C bit set with positive errno.
+         * Encode this for use in bsd-user as -errno:
+         */
+        jnb     2f
+        neg     %rax
+2:
+#endif
         pop     %rbp
         .cfi_remember_state
         .cfi_def_cfa_offset 8
-- 
2.33.0